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Chapter 1

Introduction – Identifying the Challenge

Public Health 4030

8/28/2017 1

Identifying the Challenge

• If human civilization lasts, if it continues to

spread, infectious diseases will increase in

number in every region of the globe.

Exchanges and migrations will bring the

human and animal diseases of every country.

The work is already well advanced; its future

is assured.

-Charles Nicolle, The Destiny of Infectious Diseases, 1932

8/28/2017 2Ch. 01 - Introduction

Characteristics of Microbes

• Microscopic and single-celled (usually)

• Most microbes are beneficial – Essential to the cycles of nature

required for higher life forms to exist (bacteria especially)

– Beneficial and even essential for human health

• Primary objective of this course… – Explore microbes that are capable

of causing illness and/or death (a small number of microbial species)

8/28/2017 3Ch. 01 - Introduction

There are five recognized types of microbe:

1. Bacteria

2. Viruses

3. Protozoa

4. Fungi

5. Algae (Unicellular)

(Prions make six. They, like viruses, are subcellular. But

prions are composed entirely of protein; they have

no DNA or RNA genome.)

Primarily talk about these microbes in this course

8/28/2017 4Ch. 01 - Introduction

The Challenge: In the past three decades, forty previously

unknown infectious diseases have emerged and or reemerged.

10th Surgeon General William H. Stewart (1967) - “The time has come to close the book on infectious diseases. We have basically wiped out infection in the United States.”

8/28/2017 5http://outbreaks.globalincidentmap.com/home.php

Table 01.01: Examples of New, Emerging, and Reemerging Infections.

8/28/2017 6Ch. 01 - Introduction

In 2007, infectious diseases were the second leading

cause of death worldwide.

Figure 01.02: The five leading causes of death from disease.

8/28/2017 7Ch. 01 - Introduction

Despite the major strides in control over the past century,

infectious disease remains a leading cause of death in the U.S.

8Ch. 01 - Introduction

Factors Responsible for Emerging Infections

8/28/2017 9Ch. 01 - Introduction

World Population Growth

• By 2050, the population will have soared to over nine

billion.

• 80% of the human population lives in those less-

developed countries that are least able to cope with the

problems associated with population growth.

Figure 01.04: World population, 1950 to 2050.

Source: United Nations. World Population Prospects: The 2010 Revision.

10Ch. 01 - Introduction

What does this mean for infectious diseases?

Thomas Malthus (1776-1834) • Preacher who warned two centuries ago that

unchecked population growth would lead to famine.

• The hub of the problem of population growth is

increased transmission of infectious agents.

Figure 01.05: Population explosion: the “hub” of the problem.

8/28/2017 11Ch. 01 - Introduction

World Population Growth (cont.)

• High population density facilitates the transmission of infectious disease.

population density = the number of people / area of defined size

• An aging population also contributes to the problem:

– The elderly are more susceptible to infection, thus serving as an increasing reservoir for infectious agents.

8/28/2017 12Ch. 01 - Introduction

Is this always the case? Tokyo, Japan

Overpopulation facilitates all modes of

infectious disease transmission.

Types of transmission

• Person-to-person

• Biological vector (e.g., mosquito, tick, fly,

etc., to human) HOW???

• Zoonotic (animal to human) HOW???

8/28/2017 13Ch. 01 - Introduction

Table 01.03: Potential Effects of World Population on Variables Related to Emerging and Reemerging Infections.

8/28/2017 14Ch. 01 - Introduction

Urbanization

• More of the world’s population is becoming concentrated in cities.

• Poverty challenges sanitation standards and hygiene.

Figure 01.06: Progressive urbanization of our planet.

8/28/2017 15Ch. 01 - Introduction

Figure 01.07: Poverty is especially serious where rapid

population growth occurs.

Urbanization and poverty combine to increase

infectious diseases.

Figure 01.08: Relationships among poverty, urbanization, and infectious disease.

8/28/2017 16Ch. 01 - Introduction

Sub-Saharan Africa, home to 68% of the world’s people living with HIV.

Figure 01.09: Global distribution of HIV in 2009.

Data from: UNAIDS 8/28/2017 17Ch. 01 - Introduction

Cities lacking in sanitation, safe drinking water, and public health

infrastructure become “graveyards of mankind.” (John Cairns)

Figure 01.10: Slums and shantytowns.

Author’s photo (RIK)

8/28/2017 18Ch. 01 - Introduction

Ecological Disturbances

Deforestation and human intrusion into remote ecosystems

contribute to the emergence of infectious diseases.

Figure 01.11: Deforestation.

Author’s photo (RIK) 8/28/2017 19Ch. 01 - Introduction

Ecological Disturbances cont.

• See increased contact with animals and

insect vectors.

– Example: HIV/AIDS

• See migration of displaced animals and

vectors into villages

– Examples: Chagas’ disease, rabies, leishmaniasis, schistosomiasis, etc.

Figure 01.12A: Leishmaniasis.

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8/28/2017 20Ch. 01 - Introduction

Ecological Disturbances cont.

• Zoonosis and the species leap.

Figure 01.13: The interspecies leap. The virus that causes AIDS jumped from chimpanzees or sooty mangabeys into humans.

Ecological Disturbances (cont.)

• Climactic changes: global change causes ecological

disturbances that increase the incidence and distribution

of infectious diseases.

Table 01.05: Infectious Diseases Linked to Climatic Changes.

8/28/2017 22Ch. 01 - Introduction

In the case of vector-borne diseases, the vector, the microbe, or

both may see increases due to rising temperature.

8/28/2017 23Ch. 01 - Introduction

• Natural Disasters – Environmental disasters

that place populations at

risk of an increased

burden of infectious

diseases.

Figure 01.14A: Flooded neighborhood in New Orleans.

Figure 01.14B: Mold damage in New Orleans

home.

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Houston – 08/2017

Ecological Disturbances (cont.)

Natural Disasters: Floods, hurricanes,

earthquakes, drought, tsunamis, etc., place

populations at risk of infectious diseases.

• Floods in Southern Africa

– increase in mosquitoes carrying malaria

– increase in cholera, lack of safe drinking water

• Drought in Eastern Africa

– famine and malnutrition deplete human immune

system

8/28/2017 25Ch. 01 - Introduction

Natural disasters cont.

Figure 01.15A: Open wound on a hand susceptible to infection.

Figure 01.15B: A diagnostic culture of Vibrio cholerae, the cause of cholera.

Courtesy of CDC

8/28/2017 26Ch. 01 - Introduction

Technological Advances

• The ability to fly from/to any world destination in

less than 24 hours means that a traveler can arrive at a

destination before showing disease symptoms.

• Insect vectors harboring microbes can also travel in

cabins and cargo holds.

Table 01.07: Jet Travel: Microbes Without Passports.

8/28/2017 27Ch. 01 - Introduction

July 2nd

7:30pm

July 3rd 6:00pm

Technological Advances (cont.)

Nosocomial infection (hospital acquired infection):

• Blood and blood products can be a source of infection:

– Examples: HIV, hepatitis, syphilis, malaria, Chagas' disease

• Organ transplants or invasive medical procedures

(biopsies, etc.) can transmit infectious agents:

– Examples: HIV, Chagas’ disease, etc.

• Patients on immunosuppressive therapy or those with

immunosuppressive disease (e.g., AIDS, etc.) are most

at risk

8/28/2017 28Ch. 01 - Introduction

Microbial Evolution and Adaptation

• Resistance to antibiotics and antimicrobials is at a crisis

level worldwide.

• The appearance of resistant bacteria is due to

adaptation and selection (i.e. Darwinian evolution),

which is accelerated by misuse. Examples:

– Prescribing antibiotics (that only work against

bacteria) for viral illness

(e.g. the flu or a cold)

– Failure of patient to complete drug regimen

8/28/2017 29Ch. 01 - Introduction

Table 01.08: Drug-Resistant Diseases.

8/28/2017 30Ch. 01 - Introduction

Human Behavior and Attitudes • Complacency: Medical advances have led to the false

assumption that prevention and control are no longer necessary. Examples of this are:

– Threatened resurgence of AIDS

– Lack of compliance with immunization regimens

• Human Migration: about 190 million people live outside their native countries.

– Internally displaced persons (IDPs) lack water, shelter, food, and hygiene, all leading to increases in infection

– Refugees transmit infectious diseases from their native lands to those with whom they come in contact in overcrowded refugee camps

8/28/2017 31Ch. 01 - Introduction

Human Behavior and Attitudes (cont.) Societal Factors

• Increased use of day care and preschools increases childhood illness

• Increased population of elderly means more residents in nursing homes, which are a source of infection

• Globalization and centralization of the food supply lead to widespread outbreaks of foodborne illness

• Increased numbers tattooing and body piercing, leading to infection

8/28/2017 32Ch. 01 - Introduction