course reflection 1-2 paragraphs
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COH601Week2Lecture.pptx
COH601 Global Public Health
Voice-over: Welcome to Week Two of COH601 “Global Public Health.”
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Week Two Navigation Menu
Cultural Determinants of Health
Social Determinants of Health
Disease Pathogens
2014 Ebola
Non-Communicable Diseases
Nutrition & Global Health
VO: To get started, click on the session that you want to begin.
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Module 1: Cultural Determinants of Health
VO: Module 1: Cultural Determinants of Health.
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What is Culture?
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VO: Culture is defined as, “Complex whole which includes knowledge, belief, art, morals, law, custom, and any other capabilities acquired by man as a member of society” (Taylor, 1871).
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Modern Definition
Set of rules/standards shared by a society
Which when acted upon by members
Produce behavior considered proper/acceptable
VO: The modern definition of culture “is a set of rules or standards shared by members of a society, which when acted upon by the members, produce behavior that falls within a range of variation the members consider proper and acceptable.”
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Simple Definition
Behavior/beliefs:
Learned
Shared
VO: The simple definition of culture “behavior and beliefs that are learned and shared.”
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Domains
Family & social groups
Individual growth/development
Religion, art & music
Economy, politics & law
Communication
VO: Culture operates in the domains: the family and social groups; individual growth and development; religion, art, and music; economy, politics, and law; and communication. Culture is constantly modified by “lived experiences.” Culture not static.
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Determinant of Health
| Ways | Examples |
| Related to health behaviors | Attitude towards food Hygiene Birthing/breastfeeding practices |
| Determinant of perception of illness | Different beliefs about health & illness |
| Practices concerning health | Chinese & Indian medicine |
| Affects usage of health services | Some use health services as soon as ill Others only when very sick |
VO: Culture is an important determinant of health. Culture is related to people’s health behaviors. Examples include attitude towards food, hygiene, birthing, and breastfeeding practices. Culture is an important determinant of people’s perception of illness. An example is different cultures may have different beliefs about what is good health and what is illness. Different cultures have different practices concerning health and medical treatment. An example is Chinese and Indian cultures have well defined systems of medicine. Culture affects usage of health services. Examples include some use health services as soon as they feel ill, others may visit health practitioners only when they are very sick.
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Cultrual Iceberg
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VO: The cultural iceberg.
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Key Cultural Concepts
VO: Key Cultural Concepts.
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Emic vs. Etic
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VO: Insider (emic) versus outsider (etic) perspective.
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Ethnocentrism vs. Cultural Relativism
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VO: Ethnocentrism and cultural relativism shown by the Statue of Liberty fully covered with a burqa in the country of Iraq.
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Additional Cultural Concepts
Health literacy
Cultural competence
Cultural humility
Sick Role (Talcott)
VO: Health literacy. Cultural competence (cultural humility). Sick role (Talcott).
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Insider vs. Outsider View of Culture
| Emic |
| Seeks inside perspective Viewed from within |
| Focuses on one culture |
| Looks for “culturally specific behaviors” |
| Emphasizes uniqueness of cultures |
| Etic |
| Brings outside perspective As seen from outside |
| Compares psychological theories across cultures |
| Looks for universal behaviors |
| Emphasizes similarities/differences |
VO: Emic. Seeks an inside perspective. Shows culture as viewed from within. Focuses on one culture. Looks for “culturally specific behaviors.” Emphasizes uniqueness of cultures. Etic. Brings outside perspective. Shows culture as seen from outside. Compares psychological theories across cultures. Looks for universal behaviors. Emphasizes similarities and differences between cultures.
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Example: Ascaris
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VO: An emic example of ascaris is the belief that worms in children are normal. An etic example of ascaris is the worms are contracted through eggs ingested by contact with the soil.
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Ascariasis in Guatemala
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VO: Mothers would not accept deworming medication for their children since they perceived it was normal.
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Anti-Vaccination Trends in U.S.
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VO: Some educated parents in the U.S. reject vaccines as they consider vaccine unsafe for their children and unnecessary.
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Insider Explanations of Disease Causation
| Customs | Details |
| Hot vs. Cold | Beef/pork vs. fish Breastfeeding while upset |
| Blood “sick” or “well” | Irreplaceable |
| Emotional | Sorrow, envy, fright & stress causing illnesses |
| Weather causing illness | Some use health services as soon as ill Others only when very sick |
| Supernatural | Evil eye Mystical Magical |
VO: It is important to learn local customs! Hot versus cold: beef and pork versus fish, breastfeeding while upset. Blood can be “sick” or “well.” Blood is irreplaceable. Emotional. Sorrow, envy, fright, and stress seen as causing illnesses. Weather blamed for causing illness. Supernatural. The evil eye. Mystical: an act or experience involving some impersonal causal relationship, such as fate, ominous sensation. Magical: caused by an envious, affronted, or malicious person, by sorcery or witchcraft.
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Explanations of Disease Causation
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VO: Types of insider cultural explanations of disease causation.
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Ethnocentrism
Viewing other cultures through lens of own
Taking own culture as “norm”
Group solidarity & pride in heritage
Devaluing groups other than own
VO: Ethnocentrism is viewing other cultures through the lens of our own. Taking our own culture as the “norm.” Group solidarity and pride in heritage. Devaluing groups other than own.
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Challenging Ethnocentrism
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VO: Ethnocentric beliefs about White superiority were challenged in the 1950s-1970s in the Civil Rights Movements (USA) and again in 2020. African Americans protested to overturn racist laws that prohibited their access to “white facilities.” For example, waiting rooms, toilets, drinking taps. Desegregation of schools and public transport came about and unfair legislation, such as “unequal pay,” was addressed.
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Cultural Relativism
Evaluating culture on own terms
Beliefs, behaviors & values make sense within culture
“See” from perspective of another to understand
Refraining from making judgments
VO: Cultural relativism is evaluating a culture on its own terms. Beliefs, behaviors, and values of each culture make sense within that culture. Learning to “see” from the perspective of another in order to understand a culture. Refraining from making judgments of “right” and “wrong.”
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Cultural Relativism Example
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VO: For example, can we judge the wearing of the burqa in Islamic communities, simply because it differs from Western ideas about femininity?
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Module 1: Critical Thinking
Possible to always practice?
Practices we should oppose?
Scientific objectivity take precedence above all?
If line to be drawn, where?
VO: Is it possible to always practice cultural relativism? Are there practices that we, as moral beings, should oppose? Should scientific objectivity take precedence above all? If a line is to be drawn, where should it be?
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Health Literacy
Degree individuals obtain, process & understand:
Basic health information
Services to make appropriate decisions
HDL, LDL
Oncology, nephrology, gastroenterology
Systolic, diastolic
VO: Health Literacy is defined as “the degree to which individuals have the capacity to obtain, process, and understand basic health information and services needed to make appropriate health decisions.” HDL and LDL. Oncology, nephrology, and gastroenterology. Systolic and diastolic.
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Sick Role (Talcott)
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VO: Talcott Parsons (1948) says that an individual must “agree” to be considered “sick” and to take actions (or allow others to take actions) to define the state of their health, discover a remedy, and do what is necessary to become well. He says we behave in a certain way once we know we are “sick” to excuse the sick person from normal social roles and to not hold the sick person responsible for their condition.
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Module 1: Critical Thinking (2)
If in sick role what roles exempt from?
What excused from having to do?
Sick always want to get better?
Describe situation when don’t
Always excused from normal social roles?
List situations when not
VO: If you were the person in the sick role, what roles would you be exempt from? What would you be excused from having to do? Do sick people always want to get better? Describe situation when they don’t. Are people always excused from their normal social roles? List situations when they are not.
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Rituals or Cultural Practices
VO: Rituals or Cultural Practices.
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Smoking
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VO: In the Western world, a classic example is smoking. The struggle of public health campaigns to override paradigms infused in the society by advertisers and the tobacco industry until the 1960’s.
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Drinking & Other Practices
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VO: In western world, alcohol consumption versus Islamic society. In the parts of Africa and Asia, the female genital mutilation practice and foot binding in China. In the Islamic and Jewish cultures, male circumcision. Other examples? Religions plays a major role in health: positive and less than positive trends.
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Health Beliefs/Practices
Cultures vary in views:
What is illness
What causes
What should be done
View certain as affliction while others consider normal
Some believe caused by emotional stress, supernatural causes or bodily imbalance
VO: Cultures vary in views of what is illness, what causes illness, and what should be done about it. One culture may view certain signs or symptoms as an affliction while others consider them normal. Some cultures believe illness can be caused by emotional stress, supernatural causes, or bodily imbalance.
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Prevention of Illness
Different ideas about:
How to prevent
What health care should seek
Remedies providers should offer
Many taboos concern avoiding illness
Variety of ritual practices to avoid illness
VO: Different ideas about how to prevent problems, what health care they should seek, and the types of remedies that health providers should offer. Many cultures have taboos that concern avoiding illness. Wide variety of ritual practices to avoid illness.
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Diagnosis/Treatment & Health Services
Try remedy, then visit healer, then consult doctor
Affected by cost/manner provider treats socially
Efforts to improve health need to consider beliefs
VO: Common to try a home remedy, then visit a local healer, then consult a “western doctor.” “Patterns of resort” affected by cost of services, manner in which the provider treats them socially. Efforts to improve health need to consider these beliefs.
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Types of Health Services Providers
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VO: Indigenous practitioners: power of belief; diagnostics and treatment. Western biomedical practitioners. Pluralistic healers: Mix of indigenous and western biomedical medications. Other medical systems: Indian Ayurvedic, Chinese Acupuncturists.
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Understanding Other Cultures
Influences behaviors with health consequences
Not over-interpreted at expense of socioeconomic factors
VO: Culture influences behaviors that have important health consequences. Culture should not be over-interpreted at the expense of socioeconomic factors.
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Traditional Societies
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VO: In many traditional societies, the overall theme of life is not to challenge nature but to harmonize with it. In some society wealth is a social disorder when power is misused. Cultural trends are not static because people are constantly changing.
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Assessments of Health Behaviors
Insider cultural values, beliefs & behaviors
Recognition of gender issues
Extent to which helpful or harmful
Underlying motivation why behaviors taking place
Responses to different approaches to changing “unhealthy” behaviors
VO: Understanding behaviors requires assessments of: People’s insider cultural values, beliefs, and behaviors; Recognition of gender issues; The extent to which they are helpful or harmful; Underlying motivation why these behaviors are taking place; and, likely responses to different approaches to changing the “unhealthy” behaviors.
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Successful Health Communication & Promotion Programs
VO: Successful Health Communication and Promotion Programs.
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Changing Health Behaviors
| Sector | Details |
| Community-based approach | Identify problems/promote healthy behaviors Leaders need to be willing to champion |
| Mass media | Uses radio or educational performances |
| Social Marketing | Application of commercial marketing Careful market research Understanding of local culture/values |
| Health Education | Comes in many forms Conduct peer-group education Clear, provide accurate information & gear content to target group |
| Conditional Cash Transfers | Economic incentive for families who engage in healthy behavior |
VO: Community-based approach with strong community participation: Engage entire community, such as community-based outreach workers, in efforts to identify problems and promote healthy behaviors. Leaders in community need to be mobilized, willing to champion change. Mass media: Often uses radio or educational performances to get a message across. Social Marketing: Application of tools of commercial marketing to promote a behavior change. Depends on careful market research and understanding of local culture and values. Health Education: Comes in many forms such as classroom or mass media. Conduct peer-group education. Successful programs are clear, provide accurate information, gear content to target group. Conditional Cash Transfers: A government agency provides an economic incentive for families who engage in a certain healthy behavior.
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Module 2: Social Determinants of Health
VO: Module 2: Social Determinants of Health.
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Rainbow Model of Determinants of Health
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VO: Dahlgren & Whitehead (1991) Rainbow Model describes the layers of influence on an individual’s health. Individual lifestyle factors and genetic predisposition: aging, smoking, physical activity, etc. Behavioral and cultural. Socio-economic and political: greater support from family, friends, communities; participation in social activities. Environmental: safe water, good sanitation practices, clean air, healthy food, quality housing, and safe work environment. Access to quality healthcare. Social determinants of health are the social characteristics within which living takes place. Social, economic, political, legal, and material factors that affect health. Gender equality and human rights. Health inequities. Social differences in health that are avoidable and unfair. Analytic lens: social determinants of health equity (SDHE).
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Socioeconomic Factors: Education
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VO: Better educated people tend to have better health.
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Socioeconomic Factors: Illegal Workers
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VO: Illegal workers are at higher risk of developing occupational-related diseases.
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Education & Health
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VO: Educational attainment is linked with health in three inter-related ways. 1.) Education has been linked to better health through individuals’ increased health knowledge and healthy behaviors. The mechanism is likely explained in part by health literacy. 2.) Education shapes employment opportunities, which are major determinants of economic resources that influence health. 3.) Education can influence health through social and psychological factors, with greater education linked to greater perceived personal control (which has been associated with better health and healthy behaviors), higher social standing, and increased social support.
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Unequal Access to Health Services
VO: Unequal Access to Health Services.
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Hart: “Inverse Care Law”
People who need most least likely to get
Operates where care most exposed to market forces
Less where exposure reduced
VO: Julian Tudor Hart’s “Inverse Care Law”: People who need health services the most are the least likely to get them. This inverse care law operates more completely where medical care is most exposed to market forces, and less so where such exposure is reduced.
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Barriers to Access
Financial
e.g., Unable to pay or take time off to see doctor
Geographic
e.g., Too far to travel
Cultural
Class
VO: Why? Because of barriers to access. Financial barriers. For example, unable to pay, or cannot afford to take time off from work to see the doctor. Geographic barriers. For example, too far to travel. Cultural barriers. Class barriers. A person’s social class position is strongly linked to their health status.
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Social Class: Income
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VO: Social class is measured either by a person’s income or occupation.
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Social Class: Groupings
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VO: Social class groupings: upper class, middle class, working class, and underclass.
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Social Class & Health Status
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VO: People from lower social classes usually experience higher disability rates, higher morbidity rates, higher mortality rates and have lower life expectancy than people from the upper classes. It is not a statistical artifact: No matter how social class is measured, the relationship between low social class and low health status is found in every country where health statistics are collected. Note: Poverty and mental and emotional lack of self-empowerment perspective are all contributing factors. Thus, “The lower the social class, the lower the health status of people.” Reasons for the Social Class Gradient in Health: 1.) Poverty e.g. not enough money to buy proper food, being forced to live in poor quality housing in unhealthy or high crime areas. 2.) Lower class people are less well-educated and have less knowledge of healthy lifestyles. 3.) Class differences in health-related behavior. 4.) More dangerous jobs of lower-class people. 5.) More stressful lives of lower-class people (lack of perspective).
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“Downward Drift” Hypothesis
Poor health can lead to fall in social class position
e.g., Alcoholics/drug addicts, people who cannot work because of bad health, etc.
Less where exposure reduced
VO: A low social class position can have a negative effect on health. But poor health can also lead to a fall in social class position (the “Downward Drift” hypothesis). For example, people who become alcoholics or drug addicts, people who cannot work because of bad health, etc. can fall into poverty.
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Higher Income
More access:
Health care
Nutrition
Better housing
More healthy behavior
Increased social network
VO: Higher income: more access to health care, nutrition, better housing, more healthy behavior and increased social network.
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Module 2: Critical Thinking
Social inequalities in health produced?
Explains why people in certain societies with relatively low income per capita enjoy longer/ healthier lives than those in some much wealthier societies?
VO: How are social inequalities in health produced? What explains why people in certain societies with relatively low income per capita enjoy longer and healthier lives than those in some much wealthier societies?
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Module 3: Disease Pathogens
VO: Module 3: Disease Pathogens.
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Pathogens or Disease Agents
Virus
Bacteria
Protozoa
Helminths
Prions
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VO: Pathogens: A pathogen is any biological agent that can cause disease or illness in its host. These pathogens can be bacteria, viruses, protozoa, parasites, helminths, prions. The table below displays the different types of pathogens. Viruses can only reproduce inside a living cell. Examples are human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV), influenza virus and those that cause the common cold. Viruses carried by arthropods (such as mosquitos or ticks) are known collectively as arboviruses. Bacteria are single-celled organisms present everywhere, some of which can cause disease. Important bacteria causing human disease include: E. coli (urinary tract infection, diarrhea), Streptococci (wound infection, sepsis, death), Clostridium difficile (severe diarrhea, colitis, death), Mycobacterium (tuberculosis), Staphylococcus (skin boils, pneumonia, endocarditis, sepsis, death). When conditions are not conducive to bacterial growth and reproduction, bacteria form Bacterial spores (endospores) which are thick-walled cells to preserve the cell’s genetic material. This allows them to remain in a dormant state until conditions for multiplying return. Endospores can survive for extreme lengths of time. Most types of bacteria cannot change to the endospore form. Examples of bacteria capable of forming endospores include Bacillus and Clostridium. Protozoa are single-celled microorganisms that are larger than bacteria. Examples of disease-causing protozoa include amoebas and Giardia, which cause diarrhea. Helminths include roundworms, tapeworms, and flukes. They infect humans primarily through ingestion of eggs or when the larvae penetrate the skin or mucous membranes. Helminths can cause direct damage to internal organs physically and chemically, can modulate the host’s immune response, and can result in anemia and malnutrition. Prions are a form of infectious protein believed to be the cause of several neurodegenerative diseases such as Creutzfeldt-Jakob, a severe brain disease. Like viruses, prions are not considered living. They multiply by inducing the host’s proteins to refold into an abnormal shape, accumulate in, and destroy neurons.
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Pathogens or Disease Agents (2)
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VO: A host is a living organism on or in which a parasite lives. There are different types of hosts. Primary host is one in which a parasite reaches maturity and, if possible, reproduces sexually. Secondary or Intermediate host harbors a parasite only for a short transition period during which some development stage may be completed. Paratenic Host is a potential or substitute intermediate host that serves until the appropriate definitive host is reached, and in which no development of the parasite occurs; it may or may not be necessary to the completion of the parasite’s life cycle. Accidental host is one that accidentally harbors an organism that is not ordinarily parasitic in that particular species. Reservoir host can harbor a pathogen indefinitely with no ill effects.
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Natural Reservoir
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VO: The reservoir of an infectious agent is the habitat in which the agent normally lives, grows, and multiplies. A natural reservoir is a host that does not experience disease when infected by the pathogen. In some books and websites, you may find a different definition of “reservoir.” The terminology “reservoir” is sometimes used interchangeably as “host” as defined earlier. There are three main types of natural reservoirs. 1.) Human: Asymptomatic or passive or healthy human carriers are those who never experience symptoms despite being infected. Human reservoirs or carriers commonly transmit disease because they do not realize they are infected, and consequently take no special precautions to prevent transmission. Asymptomatic or passive or healthy carriers are those who never experience symptoms despite being infected. 2.) Animals: Humans are also subject to diseases that have animal reservoirs. Many of these diseases are transmitted from animal to animal, with humans as incidental hosts. Examples: deer ticks (which may carry Lyme disease bacteria), raccoons (which may carry the rabies virus), or fish (which may carry parasites that humans ingest). 3.) Environmental: Plants, soil, water, air, and inanimate objects (fomites) in the environment are also reservoirs for some infectious agents. Many fungal agents, such as those that cause histoplasmosis, live and multiply in the soil. Outbreaks of Legionnaires disease are often traced to water supplies in cooling towers and evaporative condensers—these are environmental reservoirs for the causative organism Legionella pneumophila. Examples of inanimate objects include tissues, doorknobs, telephones, bed linens, toilet seats, and clothing. Environmental reservoirs can be: Water from fish tanks or flower vases, which may contain pathogens and are especially dangerous for compromised patients, Air filters that have not been properly maintained, sinks, soiled linens and gloves, needles or sharps, or inadequately sterilized instruments.
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Emerging Infectious Diseases (EIDs)
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VO: The Disease Triangle represents a simple concept: in order for a parasite to cause pathology—that is, for “disease” to occur—the parasite must be present, a susceptible host must be present, and environmental conditions must be sufficient to result in pathology. If you chop off one side of the triangle, there will be no disease. In the diagram to the right, you can see this interaction among Pathogen or Disease Agent, Host, and Environment. “Vector” is shown in the center of this triangle to show that diseases can also be transmitted with the help of “vectors” which will be explained in the next slide.
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Vectors
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VO: A disease vector is a living agent that transfers a pathogen from one organism to another. The vector can transport the pathogen from an infected individual or its wastes to a susceptible individual or its food or immediate surroundings. Diseases carried by vectors are known as vector-borne diseases. Vectors act like “vehicles” that transport pathogens from one host to another. As shown in this figure, insect vectors are shown in the middle connecting the animals with animals or animals with humans.
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Vectors Examples
Mosquitos
Ticks
Fleas
Roaches
Lice
Sand Flies
Kissing Bugs
Snails
Mites
VO: Vectors examples include mosquitos, ticks, fleas, roaches, lice, sand flies, kissing bugs, snails, and mites.
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Zoonosis
Transmissible under natural conditions from vertebrate animals to humans
Contact with skin, bite, direct inhalation or ingestion
e.g., Rabies, plague
VO: The term zoonosis refers to an infectious disease that is transmissible under natural conditions from vertebrate animals to humans. Contact with skin, bite or scratch of an animal, direct inhalation, or ingestion (for example, eating of contaminated meat) can lead to zoonotic diseases. Long recognized zoonotic diseases include plague from rodents, anthrax from sheep, tularemia from rabbits, and rabies from bats, raccoons, dogs, and other mammals. Many newly recognized infectious diseases in humans, including HIV/AIDS, Ebola infection, and SARS are thought to have emerged from animal hosts.
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Zoonoses vs. Anthroponoses
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VO: Infectious agents vary greatly in how they transmit the disease. Diseases transmissible from humans to humans are known as anthroponoses (examples: rubella, smallpox, diphtheria). These pathogens have adapted, via evolution, to the human species as their primary, usually exclusive, host. In contrast, Zoonoses are diseases that are transmissible from animals to animals or from animals to humans, but animals are the natural reservoir for those infectious agents (example: rabies). There are directly transmitted anthroponoses (such as TB, HIV/AIDS, and measles) and zoonoses (e.g., rabies). There are also indirectly transmitted, vector-borne, anthroponoses (e.g., malaria, dengue fever, yellow fever) and zoonoses (e.g., bubonic plague and Lyme disease). The term “zoonoses” ending in “es” is plural which means multiple diseases; whereas the term “zoonosis” ending in “is” which means one single infection.
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Zoonoses vs. Anthroponoses (2)
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VO: In this figure, the darker green shaded area waving up and down represents cycles of occurrence of pathogen in wild animal reservoirs. You can see transmission of the infectious agent and amplification in people in the bright red shaded area occurs after the pathogen from wild animals moves into livestock to cause an outbreak (light green) that amplifies the capacity for pathogen transmission to people. Spillover arrows in pink shows cross-species transmission: wild animals to domestic animals; and wild animals or domestic animals to humans. All zoonoses have non-human reservoir hosts, and the dynamics of the pathogen in these hosts often determines the risk of outbreaks in people. Early detection and control efforts during appropriate time can reduce disease incidence in people and animals. Understanding of the relation between environment, wildlife population dynamics, and the dynamics of their microbes can be used to forecast risk of human infection. This risk can vary with geography, seasons, or through multiyear cycles, and can depend on factors such as changes in land use, weather, climate, or environment. Investigations into the dynamics of zoonotic pathogens in their wildlife reservoir could act as an early warning system to better inform the risk of an outbreak in livestock or people and reduce the number of cases of human disease.
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Transmission Methods: Vector-borne & Zoonotic Diseases
VO: Transmission Methods: Vector-borne and Zoonotic Diseases.
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Stages of Infectious Disease Development
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VO: Infectious diseases can be contagious during all five of the periods of disease. Which periods of disease are more likely to associated with transmissibility of an infection depends upon the disease, the pathogen, and the mechanisms by which the disease develops and progresses. The important point to remember in here is that infectious agents are transmitted every day from people who are sick as well as from those who appear to be healthy. In fact, colonized persons and persons who are incubating an infection may present more risk for disease transmission than persons who are sick because: they are not aware of their infection, their contacts are not aware of their infection, their activities are not restricted by illness, and they do not have symptoms and therefore do not seek treatment. The five stages or phases or periods of disease include the incubation, prodromal, illness, decline, and convalescence periods. The incubation period occurs in an acute disease after the initial entry of the pathogen into the host (patient). It is during this time the pathogen begins multiplying in the host. However, there are insufficient numbers of pathogens (cells or viruses) present to cause signs and symptoms of disease. Incubation periods can vary from a day or two in acute diseases to months or years in chronic diseases, depending upon the pathogen. Factors involved in determining the length of the incubation period are diverse, and can include strength of the pathogen, strength of the host immune defenses, site of infection, type of infection, and the size infectious dose received. During this incubation period, the patient is unaware that a disease is beginning to develop. The prodromal period occurs after the incubation period. During this phase, the pathogen continues to multiply and the host begins to experience general signs and symptoms of illness, which typically result from activation of the immune system, such as fever, pain, soreness, swelling, or inflammation. Usually, such signs and symptoms are too general to indicate a particular disease. Following the prodromal period is the period of illness, during which the signs and symptoms of disease are most obvious and severe. The period of illness is followed by the period of decline, during which the number of pathogens begins to decrease, and the signs and symptoms of illness begin to decline. However, during the decline period, patients may become susceptible to developing secondary infections because their immune systems have been weakened by the primary infection. The final period is known as the period of convalescence. During this stage, the patient generally returns to normal functions, although some diseases may inflict permanent damage that the body cannot fully repair.
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Incubation Periods
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VO: The incubation periods of various infectious diseases.
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Methods of Transmission
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VO: Vector and zoonotic diseases can be transmitted through closeness or contact (such as, contact with the skin, a bite or scratch from an animal host, or a bite of a vector), direct inhalation of airborne transfer (such as, anthrax spores, influenza virus), ingestion (such as, foodborne transmission, waterborne transmission, and hand-to-mouth transmission). In direct transmission, an infectious agent is transferred from a reservoir to a susceptible host by direct contact or droplet spread. Direct contact occurs through skin-to-skin contact, kissing, and sexual intercourse. Direct contact also refers to contact with soil or vegetation harboring infectious organisms. Droplet spread refers to spray with relatively large, short-range aerosols produced by sneezing, coughing, or even talking. Droplet spread is classified as direct because transmission is by direct spray over a few feet before the droplets fall to the ground. Indirect transmission refers to the transfer of an infectious agent from a reservoir to a host by suspended air particles, inanimate objects (vehicles), or animate intermediaries (vectors). Airborne transmission occurs when infectious agents are carried by dust or droplet nuclei suspended in air. Airborne dust includes material that has settled on surfaces and become resuspended by air currents as well as infectious particles blown from the soil by the wind. Measles, for example, has occurred in children who came into a physician’s office after a child with measles had left, because the measles virus remained suspended in the air. Vehicles that may indirectly transmit an infectious agent include food, water, biologic products (blood), and fomites (inanimate objects such as handkerchiefs, bedding, or surgical scalpels). A vehicle may passively carry a pathogen—as food or water may carry hepatitis A virus. Alternatively, the vehicle may provide an environment in which the agent grows, multiplies, or produces toxin. Vectors such as mosquitoes, fleas, and ticks may carry an infectious agent through purely mechanical means or may support growth or changes in the agent. Example: fleas carry Yersinia pestis in their gut and causes plague. Also, the causative agent of malaria or guinea worm disease undergoes maturation in an intermediate host before it can be transmitted to humans.
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Chain of Transmission
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VO: Infections can only spread when conditions are right. This set of conditions is referred to as the “Chain of Transmission of Infectious Diseases,” which consists of six links. When all the links are connected, infection spreads. Infection control and prevention provides the knowledge and skills to break the links in the chain and prevent the occurrence of new infections. Thus, understanding the chain of infection is at the foundation of infection prevention. The traditional epidemiologic triad model holds that infectious diseases result from the interaction of agent, host, and environment. More specifically, transmission occurs when the agent leaves its reservoir or host through a portal of exit, is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host. Link-1: Pathogens: A pathogen is any biological agent that can cause disease or illness in its host. These pathogens can be bacteria, viruses, fungi, protozoa, parasites, helminths, prions. Link-2: Reservoirs: The next link in the chain of infection is the reservoir, the usual “habitat” in which the infectious agent (pathogen) lives and multiplies. Reservoirs can be human, animal/insect, and/or environmental (such as plants, soil, and water). Microbes often require moisture to grow and reproduce, so infectious agents often require a moist or wet habitat. However, many important human pathogens survive in dry conditions, including those that live on the skin (e.g., yeast) and in the environment. In humans, the nose may harbor bacteria and viruses. The skin is another natural reservoir for yeast and bacteria. The gastrointestinal tract is a reservoir for many different types of organisms, including viruses, bacteria, bacterial spores, and parasites. Link-3: Host: A very important link in the chain of infection is a susceptible host. Susceptibility of a host depends on genetic or constitutional factors, specific immunity, and nonspecific factors that affect an individual’s ability to resist infection or to limit disease. An individual’s genetic makeup may either increase or decrease susceptibility. For example, persons with sickle cell trait seem to be at least partially protected from a particular type of malaria. Specific immunity refers to protective antibodies that are directed against a specific agent. Such antibodies may develop in response to infection or vaccine. Nonspecific factors that defend against infection include the skin, mucous membranes, gastric acidity, cilia in the respiratory tract, the cough reflex, and nonspecific immune response. Factors that may increase susceptibility to infection by disrupting host defenses include malnutrition, alcoholism, and disease or therapy that impairs the nonspecific immune response. Link-4: Portal of entry: The portal of entry refers to the manner in which a pathogen enters a susceptible host. The portal of entry must provide access to tissues in which the pathogen can multiply or a toxin can act. Often, infectious agents use the same portal to enter a new host that they used to exit the source host. For example, influenza virus exits the respiratory tract of the source host and enters the respiratory tract of the new host. In contrast, many pathogens that cause gastroenteritis follow a so-called “fecal-oral” route because they exit the source host in feces, are carried on inadequately washed hands to a vehicle such as food, water, or utensil, and enter a new host through the mouth. Other portals of entry include the skin (hookworm), mucous membranes (syphilis), and blood (hepatitis B, human immunodeficiency virus). Link-5: Portal of exit: Portal of exit is the path by which a pathogen leaves its host. The portal of exit usually corresponds to the site where the pathogen is localized. For example, influenza viruses and Mycobacterium tuberculosis exit the respiratory tract, schistosomes through urine, cholera vibrios in feces. Some bloodborne agents can exit by crossing the placenta from mother to fetus (rubella, syphilis, toxoplasmosis), while others exit through cuts or needles in the skin (hepatitis B) or blood-sucking arthropods (malaria). Link-6: Modes of transmission: An infectious agent may be transmitted from its natural reservoir to a susceptible host in different ways, either directly thru contact or indirectly thru vectors.
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Implications
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VO: Knowledge of the portals of exit and entry and modes of transmission provides a basis for determining appropriate control measures. In general, control measures are usually directed against the segment in the infection chain that is most susceptible to intervention, unless practical issues dictate otherwise. Interventions are directed at: 1. Controlling or eliminating agent at source of transmission, 2. Protecting portals of entry, and 3. Increasing host's defenses. For some diseases, the most appropriate intervention may be directed at controlling or eliminating the agent at its source. A patient sick with a communicable disease may be treated with antibiotics to eliminate the infection. An asymptomatic but infected person may be treated both to clear the infection and to reduce the risk of transmission to others. In the community, soil may be decontaminated or covered to prevent escape of the agent. Some interventions are directed at the mode of transmission. Interruption of direct transmission may be accomplished by isolation of someone with infection, or counseling persons to avoid the specific type of contact associated with transmission. Vehicle-borne transmission may be interrupted by elimination or decontamination of the vehicle. To prevent fecal-oral transmission, efforts often focus on rearranging the environment to reduce the risk of contamination in the future and on changing behaviors, such as promoting handwashing. For airborne diseases, strategies may be directed at modifying ventilation or air pressure, and filtering or treating the air. To interrupt vector-borne transmission, measures may be directed toward controlling the vector population, such as spraying to reduce the mosquito population. Some strategies that protect portals of entry are simple and effective. For example, bed nets are used to protect sleeping persons from being bitten by mosquitoes that may transmit malaria. A dentist’s mask and gloves are intended to protect the dentist from a patient’s blood, secretions, and droplets, as well to protect the patient from the dentist. Wearing of long pants and sleeves and use of insect repellent are recommended to reduce the risk of Lyme disease and West Nile virus infection, which are transmitted by the bite of ticks and mosquitoes, respectively. Some interventions aim to increase a host’s defenses. Vaccinations promote development of specific antibodies that protect against infection. On the other hand, prophylactic use of antimalarial drugs, recommended for visitors to malaria-endemic areas, does not prevent exposure through mosquito bites, but does prevent infection from taking root. Finally, some interventions attempt to prevent a pathogen from encountering a susceptible host. The concept of herd immunity suggests that if a high enough proportion of individuals in a population are resistant to an agent, then those few who are susceptible will be protected by the resistant majority, since the pathogen will be unlikely to “find” those few susceptible individuals.
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Vector-borne/Zoonotic Diseases: Humans
VO: Vector-borne and Zoonotic Diseases: Humans.
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Zoonotic Diseases: Humans
| Disease | Domestic Animal | Wild Animal | Pathogen |
| Anthrax | Cattle, sheep, goats, other herbivores | n/a | Bacteria |
| Ebola | n/a | Fruit bats, primates | Ebola |
| Influenza A | Poultry, pigs, horses | Birds, whales, seals | Influenza |
| Hantavirus | n/a | Rodents (aerosolized urine, droppings) | Hantavirus |
| Monkeypox | n/a | African rodents | Monkeypox |
| Rabies (“Hydrophobia”) | Rapid/stray dogs, cats, cattle | Skunks, racoons, foxes, coyotes, bats | Virus |
| Rift Valley Fever | Livestock (cattle, buffalo, sheep, goats, camels) | n/a | Virus |
| Tularemia (Rabbit Fever) | n/a | Rodents, rabbits, hares | Bacteria |
VO: This table shows some of the most important zoonotic diseases that affect humans, the host or the reservoir that harbors the pathogen, as well as the pathogen type. The animal host or reservoir has been further divided into domestic and wild animals, and whenever the X in present in this table, it indicates that that type of animal is not currently the predominant host or reservoir.
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Host/Reservoir
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VO: In this diagram, you can visually view the host and reservoir information presented in the previous slide. Some of the zoonotic disease spread by wildlife are Lyme disease, Hantavirus, Ebola, and SARS. Diseases spread by livestock are cowpox, rift valley fever, E. coli and mad cow disease. Some others of animal origin are rabies, anthrax, plague, avian flu, brucellosis, and TB.
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Vector-Borne Diseases: Humans
| Disease | Vector Mosquitos | Other Vectors | Primary Host/Reservoir | Pathogen |
| Malaria | Anopheles | Humans | Parasite Plasmodium falciparum, vivax, ovale, malariae | |
| Dengue | Aedes | Humans | Virus | |
| Yellow Fever | Aedes | Humans | Virus | |
| Zika Virus | Aedes | Humans, likely primages | Virus | |
| Chikungunya | Aedes | Humans, primates | Virus | |
| Japanese Encephalitis | Culex | Waterbirds, pigs | Virus | |
| St. Louis Encephalitis | Culex | Birds | Virus | |
| West Nile | Culex | Birds | Virus | |
| Filariasis | Anophele, Culex, Aedes | Humans | Roundworm | |
| Plague | Flea | Rodents | Bacterium Yersinia pestis | |
| Lyme Disease | Black-legged tick | Deer, rodents | Bacterium Borrelia burgdorferi | |
| Leishmaniasis | Sand fly | Rodent, humans, dogs | Protozoa |
VO: Vector-borne diseases in humans.
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Major Mosquito-borne Diseases
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VO: Major mosquito borne diseases: malaria, filariasis, dengue fever, zika virus, yellow fever, chikungunya, Japanese encephalitis, St. Louis encephalitis, West Nile virus.
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Common Mosquito Groups (Genera)
| Genera | Diseases | Activity | Preferences | Locations |
| Anopheles | Malaria | Dusk to dawn feeder | Prefers human blood meal but will also feed on other mammals | Fresh or salt-water marshes, swamps, rice fields, edges of rivers/streams, pools |
| Culex | West Nile Virus, St. Louise Encephalitis, Japanese Encephalitis | Dusk to dawn feeder | Prefers an avian blood meal but will also feed on other mammals | Lays eggs in stagnant, organic-rich water |
| Aedes | Dengue, Chikungunya, Zika, Yellow Fever | Primarily day feeder | Prefers human blood meal but will also feed on other mammals | Lays single egg on sides of water holding containers (flowerpots, spare tires) |
VO: Highly successful species. Female needs blood meal for protein to produce eggs and transmits pathogen that can cause illness to humans.
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Mosquito Breeding Sites: Natural
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VO: Natural mosquito breeding habitats.
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Mosquito Breeding Sites: Man-made
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VO: Tree holes, permanent water, vernal pools, swamps, salt marshes, etc.
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Vector-borne/Zoonotic Diseases: Global Burden
VO: Vector-borne and Zoonotic Diseases: Global Burden.
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Important Terms
39
VO: Endemic refers to the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area. Endemic disease is the amount of a particular disease that is usually present in a community is referred to as the baseline level of the disease. This level is not necessarily the desired level, which may in fact be zero, but rather is the observed level. In the absence of intervention and assuming that the level is not high enough to deplete the pool of susceptible persons, the disease may continue to occur at this level indefinitely. Thus, the baseline level is often regarded as the expected level of the disease. Occasionally, the amount of disease in a community rises above the expected level. Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area. Outbreak carries the same definition of epidemic but is often used for a more limited geographic area. Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people.
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Epidemic
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VO: Epidemics occur when an agent and susceptible hosts are present in adequate numbers, and the agent can be effectively conveyed from a source to the susceptible hosts. More specifically, an epidemic may result from: a recent increase in amount or virulence of the agent; the recent introduction of the agent into a setting where it has not been before; an enhanced mode of transmission so that more susceptible persons are exposed; a change in the susceptibility of the host response to the agent; and/or factors that increase host exposure or involve introduction through new portals of entry.
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Global Burden of Diseases
Vector-borne diseases: 17% of infectious diseases
Burden highest in tropical/subtropical areas
Disproportionately affect poorest
VO: The major vector-borne diseases, together, account for around 17% of all infectious diseases around the globe. The burden of these diseases is highest in tropical and subtropical areas and they disproportionately affect the poorest populations in the world, as shown in this global map.
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Mosquito-borne Diseases
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VO: Mosquito-borne diseases, such as dengue, malaria, chikungunya, yellow fever, and Zika, by far take a very large toll on humans. Especially, Malaria takes approximately 1 million people’s lives every year. On the other hand, outbreaks of new diseases such as SARS in 2002, Swine Flu in 2009, Ebola in 2014, MERS between 2012-2015, Zika in 2015 have claimed lives and overwhelmed health systems in many countries.
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Malaria Transmission Map
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VO: In this graph, you can see temporal patterns of reported cases for selected introduced vector-borne diseases, shown in red, and endemic or long-established diseases, shown in blue. Introduced pathogens can cause notable epidemics, as seen in the US from West Nile Virus and chikungunya in India. In 1999, the New York City Department of Health (NY, USA) reported a cluster of patients with meningoencephalitis associated with muscle weakness; epidemiological evidence suggested that an arbovirus was a probable cause. Clinicians and veterinarians collaborated to identify the agent as West Nile virus, but unfortunately identification and initial control efforts did not prevent the virus spreading from the east to the west coast of North America within 4 years, causing national epidemics in 2002 and 2003. Similarly, on the Indian Ocean island of Réunion in 2005, hundreds of patients had painful and disabling polyarthralgia, and a subset presented with neurological signs or fulminant hepatitis. A second wave of such symptoms in 2006 exceeded all expectations, eventually affecting more than a third of the entire population of 770,000 people. The causative agent was identified as chikungunya virus, which is also causing continuing epidemics in India, with several million cases so far. Other introductions of VBDs have caused smaller outbreaks but have been important in the expansion of the range of human populations at risk. For example, dengue virus has spread to Hawaii, Zika virus to the Micronesian island of Yap, and chikungunya virus to Europe. Whether the outbreak of chikungunya in Europe died out naturally because of the arrival of the temperate autumn or was interrupted by mosquito control efforts is unclear. A key challenge arises from the non-specificity and similarity of symptoms caused by many of these viruses, especially Zika virus, dengue, and chikungunya virus that all present with acute fever similar to many diseases endemic in the tropics, such as malaria.
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Dengue Transmission Map
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VO: Dengue in the U.S.: Southern Texas and the southeastern states are at theoretical risk for transmission of dengue and sporadic outbreaks. The virus may be imported into the United States by travelers who are returning from endemic tropical areas.
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West Nile Virus in U.S.: 1999-2018
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VO: West Nile Virus disease incidence in the U.S. by year from 1999 to 2018.
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West Nile Virus in U.S.: 1999-2018 (2)
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VO: The average annual incidence of West Nile Virus disease in the U.S. by county from 1999 to 2018.
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2018: Zika Transmission
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VO: Zika Virus transmission risk globally in the year 2018.
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2018: Lyme Disease Transmission
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VO: Each dot represents one case of Lyme disease and is placed randomly in the patient’s county of residence. The presence of a dot in a state does not necessarily mean that Lyme disease was acquired in that state. People travel between states, and the place of residence is sometimes different from the place where the patient became infected.
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2010-2015: Human Plague
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VO: The number of reported human plague from 2010 to 2015.
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1976-2020: Ebola Virus Outbreaks
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VO: The number of reported cases of Ebola virus outbreak by species in Africa from 1976-2020.
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U.S. Distribution of Rabies
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VO: Cases of rabies among wildlife in the United States, by year and species from 1967 to 2017.
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2008-2015: Major Rabies Virus Variants
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VO: Major rabies virus variants in animal population from 2008 to 2015 in the U.S.
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Neglected Tropical Diseases (NTDs)
VO: Neglected Tropical Diseases (NTDs).
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Burden of NTDs
1+ billion infected with one or more
Most common afflictions of world’s poorest
Impede child development
Harm pregnant women
Cause long-term debilitating illness
VO: More than 1 billion people infected with one or more of the NTDs. Most common afflictions of world’s poorest people. Impede child development, harm pregnant women, and cause long-term debilitating illness.
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Major NTDs Ranked by Prevalence
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VO: The major neglected tropical diseases ranked by prevalence.
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Countries with Five or More NTDs
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VO: Countries with five or more neglected tropical diseases (NTDs).
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Consequences of NTDs
Impact on blindness, anemia, growth retardation & permanent disability
Increase susceptibility to other diseases
Social stigma
Impact on productivity
VO: Major impact on health including, but not limited to blindness, anemia, growth retardation, and permanent disability. Increase susceptibility to other infectious diseases. Social stigma. Impact on productivity.
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Emerging & Re-emerging Diseases
VO: Emerging and Re-emerging Diseases.
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Definition
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VO: Refers to infectious diseases that are caused by either apparently new agents or by known agents that occur in locales or species that previously did not appear to be affected by these known agents.
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Emergence of Zoonoses
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VO: Over the past three decades the incidence of Emerging Infectious Diseases has risen in humans, with around 70% being zoonotic in nature and most being caused by viruses and drug-resistant pathogens. This has led to increased numbers of human fatalities. Influenza viruses that originate from birds account for an important proportion of these deaths, and recently many new zoonotic viruses that originate in bats, such as Hendra virus, Nipah virus, and severe acute respiratory syndrome (SARS) coronavirus, have caused outbreaks with high mortality rates. The severe acute respiratory syndrome (SARS) epidemic in 2003–2004 claimed more than 800 lives and cost the global economy over US$80 billion. It was shown to have involved virus transmission from bats to cats to humans. In 2012, a novel coronavirus emerged in the Middle East (Middle East respiratory syndrome coronavirus (MERS-CoV)) with a 45% mortality rate for the 138 confirmed cases. Highly pathogenic H5N1 avian influenza virus has decimated poultry production in Asia and has claimed more than 350 human lives since 2003, with regular disease outbreaks continuing to occur. A new strain of influenza virus (H7N9), which has never previously been seen in humans, appeared in April 2013. Although this current strain of the avian influenza virus is not in a form that is able to transmit from human to human, there is still the possibility that it could mutate and trigger a serious pandemic. Over the past two decades, Hendra virus in Australia, Nipah virus in Malaysia and Bangladesh, and haemorrhagic fever viruses (Ebola and Marburg) have emerged from bats through intermediate hosts such as horses and pigs to infect and kill humans.
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Severity of Emerging Zoonotic Diseases
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VO: Many zoonotic agents cause little or no signs of disease in their natural hosts, such as wild birds but might present with disease symptoms ranging from moderate (for example, pigs infected with avian influenza virus) to severe (for example, horses infected with Hendra virus). The terminal or spillover host can present with severe symptoms and high mortality rates (for example, in the case of humans infected with H5N1 influenza and Hendra virus). For some of the most recently identified emerging infectious diseases, such as H7N9 influenza and Middle East respiratory syndrome (MERS) coronavirus, natural and transmission hosts have not been conclusively identified (indicated by a question mark in the figure). SARS stands for severe acute respiratory syndrome. One example is the case of highly pathogenic avian influenza. Waterfowl are natural hosts for avian influenza viruses, and after infection with the virus, they develop what seems to be a limited inflammatory response of the respiratory system, usually with little or no mortality. By contrast, in chickens and in humans, infection with the same viruses can induce a rapid and strong inflammatory response and high levels of cytokine production, and the infection can become systemic and induce severe disease symptoms. Chickens are acutely susceptible to infection with H5N1 strains of the virus, which typically cause death within 18-36 hours. Studying waterfowl, such as ducks, and comparing their immune responses to influenza virus with those of chickens might provide invaluable insights into the ‘aberrant’ immune reactions that occur in influenza virus spillover hosts, such as chickens, pigs and humans. Moreover, under-standing the mechanisms by which some recent isolates of H5N1 viruses cause systemic disease and death in ducks will help to identify the elements of the immune response that are involved in disease lethality. Another interesting example is Hendra virus, which does not cause disease in fruit bats, the natural reservoir for this virus, but induces severe disease in horses and humans. For example, the fact that infectious agents, such as henipaviruses and lyssaviruses, which cause lethal diseases in humans, can coexist peacefully with bats raises many questions. It is still unclear what role the bat immune system has in keeping these pathogens under control and in enabling host survival while allowing enough viral replication to facilitate the transmission of the virus to spillover hosts.
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U.S. Trend in Lyme Disease
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VO: These two maps show the reported cases of Lyme disease in 2001 and 2014 for the areas of the country where Lyme disease is most common (the Northeast and Upper Midwest). It has become clear that both the distribution and the numbers of cases have increased since 2001. Lyme disease is a classic example of a microbial threat influenced by multiple environmental determinants. The principal vector in North America is the black-legged tick which must take blood meals as larva, nymph, and adult to survive and reproduce. Wild rodents in the northeastern and midwestern United States serve as reservoirs for the bacterial agent of Lyme disease, Borrelia burgdorferi, but white-tailed deer are the definitive hosts for the adult ticks. The emergence of the disease has been linked in part to the reforestation of former farmland, which led to a dramatic increase in the distribution and abundance of white-tail deer populations. People become infected when they encounter the tick vector, usually during outdoor recreation or near residences in wooded areas. Prior to the reforestation of land formerly cleared for farming, Lyme disease was unrecognized. Lyme disease has increased in incidence and geographic distribution in the past 10 years in the continental United States, and as people continue to build homes and expand their neighborhoods even farther into reforested areas, the number of cases continues to rise. Thus, possible reasons can be attributed to climate change as well as reforestation and increase human outdoor activity in tick-prone areas.
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Dam Building & Rise of Disease
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VO: Environmental changes involving dam-building and irrigation projects appear to be allowing the spread of schistosomiasis, malaria, river blindness, and rift valley fever to new areas.
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Senegal River Basin
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VO: The development of dams in the Senegal River basin, for example, is among the major factors leading to a significantly increased prevalence of schistosomiasis over a period of only three years.
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Egypt: Aswan High Dam
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VO: Similarly, the Aswan High Dam has been implicated in increased rates of schistosomiasis in Egypt.
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Rise of Infectious Diseases Factors
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VO: The various factors associated with a rise of emerging and re-emerging infectious diseases can be categorized into four broad domains: genetic and biological factors; physical environmental factors; ecological factors; and social, political, and economic factors. Changes to these factors impact how microbes interacts with humans to cause a rise of infectious disease. As you examine the individual factors, envisioning each as belonging to one or more of these four domains may simplify the understanding of the complex dynamics of emergence. 1.) Genetic & Biological Factors: Microbial adaptation and change continually challenge our responses to disease control and prevention. Because microbes reproduce so quickly—as often as every 10 minutes—even very rare mutations build up rapidly in viral and bacterial populations. Microbes have enormous evolutionary potential and are continually undergoing genetic changes that allow them to bypass the human immune system, infect human cells, and spread disease. For example: the influenza virus is renowned for its ability to continually genetically evolve so that new strains emerge each year, giving rise to annual epidemics and necessitating the ongoing development of new influenza vaccine strains. 2.) Physical environmental factors: Many elements of the physical environment influence humans directly; determine the survival of pathogens that exist outside the host; and mediate the transmission of these pathogens between hosts, including the movement from animal to human hosts. For example, elevated rainfall often creates new breeding habitats for mosquitoes, leading to an increase in mosquito population density. Increased levels of precipitation can also lead to decreased marsh salinity, which in turn may increase the survival rates of certain toxic aquatic bacteria. Likewise, these same factors can affect human behavior or exposure to infection by impacting outdoor activities, housing, the quality and quantity of food, and agricultural or other uses of the environment. Among the numerous elements of the physical environment that influence the emergence of infectious diseases, climate and weather have received a great deal of attention in recent years. More about the effects of climate change later. 3.) Ecological factors: Forest growth, for example, usually reduces evapotranspiration; cropping often increases local relative humidity; and the development of large urban areas generally leads to an accumulation of atmospheric particulates and warmer air temperatures. Even very minor ecological changes, such as implementing a new farming technique, can confront pathogens with new environments and significantly alter the transmission patterns of infectious diseases. Environmental and ecological factors are playing an increasingly important role in disease emergence. In general, changes in the environment tend to have the greatest influence on the transmission of microbial agents that are waterborne, airborne, foodborne, or vector-borne, or that have an animal reservoir. 4.) Social, political, and economic factors: Host susceptibility to infection is aggravated by malnutrition. Malnutrition diminishes human’s resistance to infection through a number of mechanisms. Virtually all bodily processes and physical barriers that keep infectious agents from invading the host are affected. These include the skin, mucous membranes, gastric acidity, absorptive capacity, intestinal flora, cell-mediated immunity, phagocyte function, and cytokine production. A strong and consistent relationship has been found between childhood malnutrition and increased risk of death from diarrhea, acute respiratory infection, and possibly malaria. Malnutrition has risen as a result of population growth in the region, as well as natural disasters, wars, civil disturbances, and population displacement.
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Contributing Factors
| Disease | Agent | Factor(s) Contributing to Emergence |
| Mad Cow Disease (Bovine Spongiform Encephalopathy) | Prion | Changes in rendering process |
| Dengue | Virus | Transportation, travel and migration, urbanization |
| Ebola | Virus | Unknown |
| Hantavirus | Virus | Ecological/environmental changes, increasing rodent contact |
| Rift Valley Fever | Virus | Dam building, agriculture, irrigation, possible change in virulence or pathogenicity |
| Escherichia coli | Bacteria | Mass food processing technology allowing contamination of meat |
| Lyme Disease | Bacteria | Reforestation around homes, suburbanization & other conditions favoring tick vector/deer population |
| Cryptosporidium | Protozoa | Contaminated surface water, faulty water purification |
VO: The physical environment is constantly being modified by human activities. Most economic development activities, including the consumption of natural resources, deforestation, and dam building, have some intended or unintended impact on the environment, or both. In the present context, it is important to note that a growing number of emerging infectious diseases arise from increased human contact with animal reservoirs as a result of changing land use patterns. Examples include increases in malaria following the clearing of land for rubber plantations in Malaysia; increases in schistosomiasis, malaria, and other infectious diseases following the Volta River project in Africa; increases in vector-borne diseases after the construction of new transportation routes in Brazil; and the emergence of Lyme disease in the United States after the reforestation of abandoned farmlands in the northeast. Even the emergence of HIV is believed to have been due to increased contact with nonhuman primates infected with the related simian immunodeficiency viruses (SIVs); exposure to infected blood during the hunting and field dressing of animals and the preparation of primate meat for consumption may have led to human infection.
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Key Factors
62
VO: The various environmental changes that affect the occurrence of various infectious diseases in humans. The ecological and biological factors have been explained earlier. In here, we will expand on the other factors that led to a rise in emerging and re-emerging infectious diseases.
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Rise of Infectious Diseases Examples
63
VO: The emergence and reemergence of vector-borne pathogens are linked to changes in temperature (which determines how long it takes the parasite to develop), wind speed, and relative humidity (all of which affect vector feeding frequency); the amount and diversity of vegetation; and the presence of alternative hosts (which can alter the rate of blood feeding on humans). In particular, as previously discussed, global warming could theoretically result in dramatic alterations in the incidence and distribution of vector-borne diseases. Mosquito abundance and transmission of pathogens are typically associated with rainy seasons since juvenile mosquitoes develop in aquatic habitats. Dengue transmission, for example, typically occurs during the rainy season. Populations of floodwater- and container-breeding mosquitoes (e.g., Ae. aegypti) are dramatically affected by environmental conditions; their abundance is directly linked to rainfall or snowmelt, which induces the eggs to hatch. Human Demographics and Behavior: The opportunity for transfer of a microbe from one human to another has grown with the explosion of the world’s population. People are also rapidly moving to urban settings by choice or circumstance, leading to close contacts conducive to the spread of infection. Increases in life expectancy, growing number of immunocompromised individuals, international migration, and rural to urban migration lead to the spread of communicable diseases. Technology and Industry: New infectious diseases have emerged as a direct result of changes in technology and industry; these include Legionnaires’ disease (air-conditioning cooling towers), toxic shock syndrome (super-absorbent tampons), and E. coli O157:H7 infection (mass production of ground meat). Even the manner in which animals are raised before entering the meat processing industry, such as the use of antimicrobials for growth production and concentrated amount of animal waste produced in farmland, can impact on microbial threats to health. International Travel and Commerce: The potential for the rapid dissemination of pathogens, and their vectors and animal reservoirs, throughout the world is increasing greatly as the world continues to experience expanding global trade markets and increasing international travel. Infections that are carried by humans and transmitted from person to person—including influenza, measles, rubella, HIV, tuberculosis—are especially amenable to being carried from one geographic area to another. Microbes that can colonize without causing symptoms or can infect and be transmissible at a time when infection is asymptomatic (e.g., HIV, hepatitis B and C) can spread easily in the absence of recognized infection in traveling or migrant hosts. Modern technologies have expanded the range of easily accessible destinations and allow travelers to enter and survive more extreme environments and encounter more isolated human populations. Not only can infected travelers introduce new microbes into new environments, both while traveling and after having returned home, but, as adventure travelers intrude on new environments and have contact with exotic wildlife, the chance that they will come into contact with microbes that have never before been recognized as human pathogens is real. They may then bring these exotic infectious agents back home with them, where, under appropriate circumstances, an introduced pathogen may persist and spread. Besides air travel, cruise ships are also very susceptible to these problems. The movement of goods and people can also support the movement of vectors, allowing them to become established in new areas. Ae. aegypti apparently spread to coastal areas of Africa and was then transported throughout the world in sailing ships. Presumably Ae. aegypti, as well as yellow fever virus, was introduced into the New World on slave ships. Ae. albopictus, the Asian tiger mosquito, likely entered the United States via shipping. Food imports is also a cause of concern! During the winter months, 25 percent of cantaloupe and 50 percent of tomatoes consumed in the United States are imported from Mexico. These examples of imported produce, as well as others, have been implicated as vehicles in foodborne outbreaks. Breakdown of Public Health Measures: A breakdown or lack of public health measures, such as adequate sanitation, immunizations, and tuberculosis control, has had a dramatic effect on the emergence and persistence of infectious diseases throughout the world. For example, infectious diseases have resurged in the former Soviet Union after the country’s enormous socio-economic upheavals and the fracturing of its health services that has resulted from poor funding for treatment, vaccine prophylaxis, and health education. Even the United States has had difficulties maintaining adequate supplies of vaccines in recent years, and immunization rates for adults are still far below national targets. Inadequate Sanitation and Hygiene: Poor sanitary conditions and a lack of proper hygiene contribute to the transmission of many infectious diseases. To date, one of the most significant shortages worldwide is that of potable water. This shortage has implications for the transmission of numerous infectious diseases, such as cholera. Squalid living conditions with overcrowding and the presence of vermin also contribute to the spread of infections, such as plague. Poverty and Social Inequality: The structure of health care delivery, in turn, profoundly affects the ability of high-risk populations to pursue health care. For example, the transmission of illnesses such as TB, which nearly disappeared in affluent countries after the introduction of effective antimicrobial therapy in the 1950s, has continued to rise in poor countries. It is not coincidental that many of the latter countries have been hardest hit by microbial threats to health such as HIV, dengue, drug-resistant TB, and malaria. The relationship between infectious diseases and economic development has been of increasing interest to scholars and practitioners in a variety of fields. It is important to note that the arrow points in both directions: not only do infectious diseases have significant and far-reaching economic implications, but poverty and social inequality in and of themselves are major factors in disease emergence. Socioeconomic status is often implicated in public health trends that might appear at first glance to be unrelated. For example, chronic infection with hepatitis B virus has been associated with low educational attainment, lower social stratum, and crowded urban residence. In 1990, developing countries spent $41 per person on health, compared with $1,500 per person in industrialized countries. This underfunding creates a chronically inadequate or erratic supply of drugs, which, combined with several other factors, such as transportation costs and the high costs of medical treatment and drugs, leads to poor patient compliance. War and Famine: War and famine are closely linked. Not only do they both lead to severe disruptions in food distribution and consumption, but in fact a frequent causal relationship exists between the two. So-called “complex humanitarian emergencies” provoked by the combined conditions of famine and war contribute directly to the spread of infectious, such as, measles, diarrheal diseases, respiratory tract infections, and malaria. For example, in 1994 more than a million Rwandan refugees were sheltered in Goma, Democratic Republic of the Congo, formerly known as Zaire, when cholera and dysentery swept through the camps, killing 12,000 people in just 3 weeks. In the post-conflict phase, malaria accounted for over one-third of the total mortality among displaced populations in Central Africa in the aftermath of the Great Lakes crisis of 1994, and TB was estimated to have caused one-fourth of all deaths among refugees in Somalia in the 1990s. Lack of Political Will: The need for political will to fight microbial threats is still invoked frequently. Many possible opportunities have been lost as a result of this lack of political will and a general complacency toward infectious diseases at the end of the twentieth century. Intent to Harm: The threat of intentional attacks using biological agents on the United States and other countries has never been as serious as it is today. Examples of biological weapons are Ebola for use as weapon. Botulin and anthrax, plague bacillus.
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Direct Climate Effects on Disease Vectors
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VO: Climate can affect disease transmission in a variety of ways. The distribution and population size of disease vectors can be heavily affected by local climate. Vectors, pathogens, and hosts each survive and reproduce within a range of optimal climatic conditions: temperature and precipitation are the most important, while sea level elevation, wind, and daylight duration are also important. Rainfall can influence the transport and dissemination of infectious agents, while temperature affects their growth and survival. In addition, there is some evidence to suggest that pathogens can be spread from one region to another along air streams or by wind. Rising global temperatures can lengthen the season and increase the geographic range of disease-carrying insects. As temperatures warm, mosquitoes and other warm-weather vectors can move into higher altitudes and new regions away from the equator. For instance, in some regions in the United States, warming is lengthening the season for Zika-carrying mosquitoes. There is mounting evidence that certain vectors, such as Aedes mosquitos, are mostly changing their range. For example, dengue fever, chikungunya and West Nile virus are emerging in areas where they were previously unknown and there is mounting evidence that this is due, in part, to increasing temperatures, along with other factors, such as increasing global travel and trade. While there is less research on Zika, the same vectors facilitate its spread, which scientists say points to increased risk in some regions. Increased rainfall, flooding and humidity creates more viable areas for vector breeding and allows breeding to occur more quickly, as eggs hatch faster in hotter climates. For example, there was an increase in risk for Zika and West Nile virus infections after the massive flooding event in Louisiana in August 2016, which increased the breeding habitats for Aedes mosquitoes. There are scientifically documented relationships between climatic variables and biological parameters, such as, vector breeding, survival, and biting rates, and parasite incubation rates. Insect vectors have several physical traits that help them take advantage of climate impacts. Insects cannot regulate their body temperature and are dependent on external warmth to survive. Rising temperatures may cause vector range patterns to shift, increasing the risk to new populations. Humidity and water are crucial for vector breeding, so more insects can hatch in areas with standing water and high precipitation. The incubation period of pathogens within vectors is also temperature-dependent and becomes shorter in warmer conditions. Malaria is of great public health concern and seems likely to be the vector-borne disease most sensitive to long-term climate change. Malaria varies seasonally in highly endemic areas. The link between malaria and extreme climatic events has long been studied in India, for example. Early last century, the river-irrigated Punjab region experienced periodic malaria epidemics. Excessive monsoon rainfall and high humidity was identified early on as a major influence, enhancing mosquito breeding and survival. Recent analyses have shown that the malaria epidemic risk increases around five-fold in the year after an El Niño event. Globally, temperature increases of 2-3ºC would increase the number of people who, in climatic terms, are at risk of malaria by around 3-5%, i.e. several hundred million. Further, the seasonal duration of malaria would increase in many currently endemic areas.
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Module 4: 2014 Ebola
VO: Module 4: 2014 Ebola.
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Ebola Strains
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VO: Strains of Ebola Virus that can infect humans are Zaire ebolavirus (EBOV), Sudan ebolavirus, Bundibugyo ebolavirus, Reston ebolavirus, and Tai Forest ebolavirus.
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Zaire Strain
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VO: Zaire strain is the deadliest and is the one spreading in the 2014 outbreak. Order: Mononegavirales. Member: Filovirus. Family: Filoviridae. Genus: Ebolavirus. Species: Zaire ebolarivus.
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Geographic Distribution
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VO: The geographic distribution of Ebola virus disease outbreaks in humans and animals.
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Past Ebola Outbreaks
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VO: 1976: Ebola was first discovered in Zaire (now known as the Democratic Republic of Congo).
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Ebola Transmission
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VO: Possible Ebola animal to human transmission chain.
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Modes of Transmission
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VO: Modes of Ebola transmission.
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Signs & Symptoms
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VO: “Although victims may appear healthy, they are still infectious as long as their blood and secretions contain the virus. Men who have recovered from the disease can still transmit the virus through their semen for up to 7 weeks after recovery.” There is no cure, treatment, or vaccine for Ebola.
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How Ebola Attacks Humans
Direct contact
Infected feces, vomit or blood
Younger = better chance of survival
Sooner seek medical = better chance for survival
VO: Direct contact with virus needed. Infected feces, vomit, blood, and, to a lesser extent, saliva, sweat, semen, vaginal lubrication. A little virus is all you need to contract infection. Younger you are, better the chance of survival. Over 45 years old has very high chance to die. Sooner you seek medical attention, the better the chance for survival.
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How Ebola Attacks Humans (2)
Disrupts immune system
Copies itself
Spreads: lymph nodes, liver, spleen & other areas
VO: Ebola virus disrupts the human immune system. Disable the “army” or the “defense system.” Virus makes copies of itself and spreads thru lymph nodes, liver, spleen, and other areas.
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Symptoms
| Symptom | Details |
| Low fever | |
| Loss of fluids | Diarrhea: Up to 2 gallons/day Triggers electrolyte imbalance |
| Liver damage | Leads to over-coagulation/under-coagulation Leads to leaky blood vessels Internal bleeding Compromises blood supply to liver |
VO: As number of virus rise within body, symptoms appear. Low fever. Loss of fluids in the form of diarrhea: Up to 2 gallons per day; Triggers electrolyte imbalance; Important to keep hydrated, main battle, very difficult! Liver damage leads to over-coagulation of blood in some areas and under-coagulation in other areas. Leads to leaky blood vessels. Internal bleeding. Compromises blood supply to the liver. Analogy: hose full of holes to water a garden, water does not get where is needed.
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Sepsis
Bacteria from GI tract slips into blood stream
Causes sepsis
Blood pressure plummets
Organ fails
Shock
Death
VO: At this point, bacteria from GI tract slips into blood stream and causes sepsis. Blood pressure plummets, organ fails, patient goes into shock and dies.
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Cultural Practices/Beliefs
| Action | Result(s) |
| Spray chlorine on bodies/hands | Villagers do not like |
| Bodies not shown to relatives | Think health workers selling organs |
| Hazmat suit | An alien |
| Communities promote spread | Burial practices involving touching body |
| Families care for sick loved ones | Sick person will infect family members |
| Incubation: 2-21 days | Movement impairs ability to track spread |
VO: Health workers spray chlorine on bodies and hands. Villagers do not like. Bodies not being shown to relatives. Villagers think that health workers are selling organs. The hazmat suit or full body covered with plastic. An alien from outer space. Another difficulty with this outbreak is that certain cultural practices in the affected communities can actually promote the spread of EBOV. for example, families of deceased patients perform traditional burial practices, which involve transporting and touching the body of the deceased family member. Additionally, because the health care infrastructure in the affected regions is often minimal, families tend to care for sick loved ones at home rather than bringing them to the hospital. This makes it very likely that a sick person will infect family members that care for them during their illness. Finally, the virus has an incubation period that varies between 2 and 21 days, meaning that a person can be infected with EBOV without experiencing any symptoms for up to 3 weeks, during which they may travel and bring the virus to previously unaffected areas. The movement of patients, together with home caregiving and traditional burial practices, impairs the ability of public health workers to track the spread of the virus.
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2014 Outbreak
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VO: Update: November 2nd, 2014.
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Countries with Widespread Transmission
| Country | Total Cases | Deaths |
| Guinea | 1760 | 1054 |
| Liberia | 6919 | 2766 |
| Sierra Leone | 4862 | 1130 |
| Total | 13241 | 4950 |
VO: Countries with widespread transmission.
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Countries with Limited Transmission
| Country | Total Cases | Deaths |
| Nigeria | 20 | 8 |
| U.S. | 9 | 1 |
| Spain | 3 | 2 |
| Germany | 3 | 1 |
| Senegal | 1 | 0 |
| Norway | 1 | 0 |
| France | 1 | 0 |
| U.K. | 1 | 0 |
| Mali | 1 | 1 |
VO: Countries with limited transmission.
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Video on Ebola
MDP: Link the image to https://youtu.be/ANUI4uT3xJI
VO: Click on the image to view the video.
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Module 5: Non-Communicable Diseases
VO: Module 5: Non-Communicable Diseases.
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Non-Communicable Diseases (NCDs)
Illnesses that:
Prolonged
Not resolve spontaneously
Rarely cured completely
VO: Illnesses that are prolonged, do not resolve spontaneously, and are rarely cured completely.
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Non-Communicable Diseases (NCDs) (2)
Characterized by:
Multiple risk factors
Long latency period
Prolonged course of illness
Noncontagious origin
Functional impairment/disability
Incurability
VO: Characterized by multiple risk factors, a long latency period, prolonged course of illness, noncontagious origin, functional impairment or disability, and incurability.
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NCDs Importance
Growing importance worldwide
Burden greater than burden of communicable diseases in low-, middle- & high-income countries
VO: Growing importance worldwide. Burden of noncommunicable diseases greater than burden of communicable diseases in low-, middle-, and high-income countries.
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Cardiovascular Disease, Diabetes & Cancer
Most important in low-/middle-income countries
Direct cost:
Very expensive to treat
Indirect costs:
Loss of productivity
Often prevented at lower cost
VO: Cardiovascular disease, diabetes, and cancer are most important in low- and middle-income countries. Cost. Direct cost: Very expensive to treat. Indirect costs: Loss of productivity. Often prevented at lower cost.
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Module 5: Critical Thinking
NDCs considered silent epidemic worldwide?
VO: Why are NDCs considered a deadly silent epidemic worldwide?
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NCDs Causes
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VO: Increased urbanization-less infections in some cases but more injuries and chronic diseases. Aging-even in low- and middle-income countries people are living longer, leading to more chronic disease. Personal behaviors-or lifestyles are highly associated with chronic disease morbidity and mortality. Tobacco use, eating behavior, physical activity, and alcohol consumption.
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Circulatory Disease: Mechanism
74
VO: Mechanism. First, Atherosclerotic (build-up of fatty deposits within arterial walls). Next, narrowing of arteries supplying blood to the heart. Then, Ischemia (denial of adequate blood supply). Ischemic heart disease also known as coronary heart disease (CHD) or coronary artery disease. A common form is myocardial infarction (heart attack). Persistence of deficient blood supply, thus, heart tissue dies. Dead area is an infarct.
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Circulatory Disease: Stages A-D
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VO: Mechanical and neurohumoral mechanisms of heart disease.
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Circulatory Disease: Risk Factors
High blood pressure leading
Smoking most preventable
High blood cholesterol levels major
Lack of physical activity most modifiable
Obesity
Related to inappropriate nutrition/inactivity
VO: Risk factors. High blood pressure is leading risk factor. Cigarette smoking is the most readily preventable risk factor. High blood cholesterol levels are also a major risk factor. Lack of physical activity is the most prevalent, modifiable risk factor. Obesity is a risk factor and is related to inappropriate nutrition and inactivity.
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30% Deaths Worldwide
Leading cause in low-, middle- & high-income countries
Accounts for significant morbidity
Rates vary by region
VO: Cause of about 30% of all deaths worldwide. Leading cause of death in low- and middle-income countries, and high-income countries. Accounts for significant morbidity. Rates vary by region.
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Cancer
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VO: Most important worldwide are lung, colorectal, breast, prostate, liver, and stomach cancers. 18 million new cases of cancer each year. More likely to be associated with tobacco use, environmental factors, and lifestyle choice. Australia has been ranked with having the highest male, female, and overall cancer rate in the world (WCRF, 2020).
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Most Common Cancers