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LIVING WITH THE EARTH

CHAPTER 7 EMERGING DISEASES

Esherichia coli on EMB plate

Objectives for this chapter • A student reading this chapter will be able

to: – 1. Differentiate the emerging infectious

diseases in the United States and those occurring worldwide.

– 2. List and recognize the 6 major reasons associated with the emergence of infectious diseases.

– 3. Explain the likely reasons for the emergence of specific infectious diseases.

Objectives for this chapter

• A student reading this chapter will be able to: – 4. Identify, list, and explain the etiological

agents, the epidemiology, and the disease characteristics of the major emerging infectious diseases including: influenza, hanta virus, dengue fever, ebola, AIDs, Cryptosporidiosis, Malaria, Lyme disease, Tuberculosis, Streptococcal infections, and E. coli infections.

Objectives for this chapter

• A student reading this chapter will be able to: – 5.Recognize and explain the practical

approaches to limiting the emergence of infectious diseases.

EMERGING DISEASES

• INTRODUCTION – Infectious diseases continue to be the foremost

cause of death worldwide. – The Centers for Disease Control and Prevention

(CDC) reported a 58 percent rise in deaths from infectious diseases since 1980.

Emerging Diseases in the United States

• Cryptosporidium • AIDS • Escherichia coli • Hanta Virus • Lyme Disease • Group A Strep

Emerging Diseases Worldwide

What is an Emerging Infectious Disease

– The term "emerging infectious diseases" refers to diseases of infectious origin whose incidence in humans has either increased within the past two decades or threatens to increase in the near future.

REASONS FOR THE EMERGENCE OF INFECTIOUS

DISEASE – There are a number of specific explanations

responsible for disease emergence that can be identified in most all cases (Table 7-1a-d).

Table 7-1a

Viral Viral diseases that have been identified since 1973 • 1977 Ebola, Marburg

– Origin undetermined. (Importation of monkeys associated with outbreaks in these primates in Europe and the United States)

• 1980 HTLV Influenza (pandemic) – Pig-duck agriculture thought to contribute to reassortment of avian and mammalian influenza

viruses

• 1983 HIV – Transmission by intimate contact as in sexual transmission, contaminated hypodermic needles,

transfusions, organ transplants. Contributing condition that spread the disease include war or civil conflict, urban decay, migration to cities and travel

• 1989 Hepatitis C – Transmission in infected blood such as by transfusions, contaminated hypodermic needles, and

sexual transmission

• 1993 Hantaviruses – Increased contact with rodent hosts because of ecological or environmental changes

Adapted from Morse.24

Table 7-1b

Viral Diseases that have re-emerged • Argentine, Bolivian hemorrhagic fever

– Agricutural changes that promote growth of rodents • Bovine spongiform encephalopathy (cattle)

– Alterations in the rendering of meat products • Dengue, dengue hemorrhagic fever

– Travel, transportation, urbanization, and migration • Lassa fever

– Coniditons such as urbanization that favor rodent host, increasing exposure (usually in homes)

• Rift Valley fever – Irrigation dam building, agriculture: possibly change in virulence

• Yellow Fever – Conditions favoring mosquito vector (in “new” areas)

Adapted from Morse.24

Table 7-1c

Bacterial Bacterial Diseases that have been identified since 1973 • 1977 Legionella disease

– Cooling and plumbing systems that allow the organisms to grow in biofilns that form on water • 1982 Hemolytic uremic syndrome (Escherichia coli- O157:H7)

– Modern food processing on a large scale permitting contamination through meat storage tanks and unsterile plumbing

• 1982 Lyme borreliosis (Borrelia burgdorfen) – Close contact between homeowners encroaching on forested areas and the mice and deer (a secondary

reservoir host) that maintain the tick vector for Borrelia • 1983 Helicobacter pylori

– Newly recognized as agent involved with gastric ulcers, probably widespread before recognition • 1987 Toxic shock syndrome (Staphyloccus aureus)

– Ultra-absorbency tampons • 1992 Cholera (type 0139)

– Likely introduced from Asia to South America by ship, with spread made possible by reduced water chlorination; Strain (type O139) from Asia newly spread by travel (similarly to past introductions to classic cholera)

Adapted from Morse.24

Table 7-1d

Bacterial Diseases that have re-emerged • Tuberculosis

– Breakdown in public health measures such as reduction in prevention programs, inadequate sanitation, homelessness, AIDS

• Streptococcus, group A (invasive necrotizing) – Unknown, may be increased use of NAIDS

Parasites Parasitic diseases that have been identified since 1973* • 1976 Cryptosporidium, other waterborne pathogens

– Contaminated surface water, lack of proper filtration methods Parasitic diseases that have re-emerged • Malaria (in “new” areas)

– Spread of mosquito vectors, worldwide travel or migration, “airport” malaria • Schistosomiasis

– Agriculture, dam building, deforestation, flood/drought, famine, climate

* Compiled by CDC staff. Dates of discovery are assigned on the basis of the year the isolation or identification of etiologic agents was reported.

Adapted from Morse.24

Factors Responsible for the Emergence of Infectious Disease

– (1) Ecological changes; – (2) Human demographic changes; – (3) Travel and commerce; – (4) Technology and industry (globalization); – (5) Microbial adaptation and change

(resistance); and – (6) Breakdown of public health measures.

Ecological Changes

• Agriculture – Agricultural or economic development – People may expand into an area where the

animal host thrives, the animal host may expand into human living areas.

Ecological Changes

• Climate – Extreme weather patterns, as a result of natural

fluctuations in the atmosphere or man-made changes (i.e., global warming) have routinely been followed by outbreaks of disease.

– El Niño, Vibrio, Hanta Virus

Human Demographic Changes

– Increased population density in urban areas- migration in hopes of a better, more comfortable lifestyle- has surpassed basic services, including clean water supplies, sanitary conditions such as sewage disposal and adequate housing.

Human Demographic Changes

– Public health measures in overcrowded cities are often strained or unavailable to large groups of the urban impoverished living in inner city slums or in shanty towns on the periphery, thereby increasing the opportunity for emerging infections such as HIV, cholera, and dengue.

Travel and Commerce

– Increased economic growth into national and international boundaries has led to increased travel, contributing to the notion of "diseases without boundaries."

Travel and Commerce

• Bubonic Plague • Smallpox • Aedes aegypti • Vibrio cholerae

Technology and Industrialization

• Globalization – Defined as the process of denationalization of

markets, laws, and politics in the sense of interlacing peoples and individuals for the sake of the common good.

Technology and Industrialization

• Globalization is influencing public health in three ways. – (1) First, the diseases are moving rapidly

around the globe because of technology and economic interdependence which has increased international travel and the international nature of food processing and handling.

Technology and Industrialization

• Globalization is influencing public health in three ways. – (2) The funding of public health programs has

been reduced because of increased competition in the global market and increased pressures to cut expenditures.

Technology and Industrialization

• Globalization is influencing public health in three ways. – (3) Public health programs have become

international through WHO and health-related nongovernmental organizations.

– These successes have contributed to a population crisis, producing overcrowding, inadequate sanitation, and overstretched public health infrastructures.

Microbial Adaptation and change (resistance)

• Antibiotic Resistance – Antibiotic-resistant bacteria are emerging from

the environment in response to the wide distribution of antimicrobials.

– Selection for antibiotic-resistant bacteria, and drug-resistant parasites have become common, generated by the wide and often unsuitable use of antimicrobial drugs.

Antibiotic Resistance

• There is growing concern that bacterial pathogens are developing a resistance to antibiotics as a result of patients not completing the prescribed course of treatment or the inappropriate and over prescribing of common antibiotics by physicians.

Antibiotic Resistance

• The use of unsupervised prophylactic tetracycline administration to 100,000 pilgrims en route to Mecca from Indonesia is thought to have been significantly responsible for the fact that 50% of cholera strains in that country are now tetracycline resistant.

Antibiotic Resistance

• Many hospitals consider Vancomycin and Rocephin their “big guns” in the disease war.

• A recent report by the CDC found that Vancomycin resistance measured at 0.3% in 1986, rose to 7.9% across several facilities in 1994.

Viruses

• Antibiotics have no effect on viruses, and vaccines are often ineffective against bacterial infections.

Breakdown of Public Health Measures

• During the eighteenth and nineteenth centuries advancements in public health vastly improved the overall health of the populace, particularly in urban settings.

Breakdown of Public Health Measures

• Vector control, chlorination of water, pasteurization of milk, immunization, and proper sewage disposal are classical public health and sanitation measures that have successfully minimized the spread of infectious diseases in humans.

Breakdown of Public Health Measures

• Well understood and recognized diseases such as cholera are rapidly increasing because once active public health measures have lapsed.

SPECIFIC EMERGING DISEASES

• Viruses – The viruses with the greatest potential for

emergence in the near future include: hantaan (hantavirus), dengue, influenza, and HIV.

Hanta Virus

• Background – Navajo Flu – CDC personnel trapped and tested rodents from

the area, they found the deer mouse, Peromyscus maniculatis primary reservoir in New Mexico.

Hanta Virus

• The Disease – The hantaviruses that emerged in the Four

Corners region of the United States were determined to be the cause of an acute respiratory disease now termed hantavirus pulmonary syndrome (HPS).

Hanta Virus

• The Disease – Initial symptoms of the American version

(HPS) were flu-like and manifested as fever, chills, headache, muscular aches and pains.

– With time the lungs fill with fluids causing severe respiratory distress for which there is no specific treatment.

Hanta Virus

• Epidemiology – The virus is spread to humans from contact

with rodents. – The most common route of transmission to

humans is by aerosolized mouse droppings containing the virus particles, although there is evidence that bites may also transmit the disease.

Hanta Virus

• Epidemiology – It is now established that hantaviruses can be

carried by at least 16 various rodent species including rats, mice, and voles.

– Investigations have linked virus exposure to such activities as heavy farm work, threshing, sleeping on the ground, and military exercises.

Dengue Fever

• Background – There are in excess of 10s of million cases of

dengue fever annually, with several hundred thousand cases of the more severe dengue hemorrhagic fever (DHF).

Dengue Fever

• The Disease – There are four antigenically distinct viral

serotypes. – There is no cross-protective immunity with any

of the viruses, so that it is possible for a person to acquire multiple dengue infections.

Dengue Fever

• The Disease – Dengue is primarily an urban tropical disease

with severe flu-like symptoms that causes high fevers, frontal headache, severe body aches and pains, nausea and vomiting.

Dengue Fever

• The Disease – When the fever eases, patients start to develop

“leaky capillary syndrome” in which the blood vessels leak and untreated patients will go into shock and die.

Dengue Fever

• Epidemiology – The greatest emerging health menace from

dengue/DHF has been in Central and South America (Fig. 7-1).

– Complacency in mosquito control programs has allowed Aedes aegypti to return with a vengeance and it is a competent vector for dengue viruses (Fig. 7-2).

Fig. 7-1Adapted from EID Dispatch.93

Fig. 7-2Adapted from EID Dispatch.93

Influenza

• Background – Types A and B are responsible for the

epidemics of respiratory influenza (Fig. 7-3). – Type C is produces very mild symptoms or

none at all.

Fig. 7-3Adapted from WHO.100

Influenza

• The Disease – Influenza is normally characterized by a fever

(100¼F to 103¼F ) ; respiratory symptoms, that include cough, sore throat, stuffy nose; muscle aches and pain; and extreme fatigue.

Influenza

• The Disease – There are about 20,000 deaths annually in the

United States with the majority of serious illness and death occurring in the aged, very young, and debilitated.

Influenza

• Epidemiology – To this date, there have been more than 30

pandemics of influenza with three occurring within the last 80 years.

– The Spanish Flu (1918-19) caused an estimated 500,000 deaths in the United States and 20 million deaths worldwide.

Ebola

• Background – Ebola and Marburg viruses belong to a family

of viruses called Filoviridae (Fig. 7-4). – Their extreme pathogenicity combined with the

lack of effective vaccines or antiviral drugs classify them as biosafety level four agents.

Fig. 7-4

Ebola

• The Disease – Ebola fever typically starts suddenly 4 to 16

days after infection with malaise, fever and flu- like symptoms which can be followed by rashes, bleeding and kidney and liver failure.

Ebola

• The Disease – Generalized bleeding occurs with massive

internal hemorrhaging of the internal organs, with bleeding into the gastrointestinal tract, from the skin, and even from injection sites as the clotting ability of the blood is diminished.

Ebola

• The Disease – The death of the patient usually occurs from

shock within 7 to 16 days and is accompanied by extreme blood loss.

Ebola

• Epidemiology – Infections from Ebola virus were first reported

in 1976 when two outbreaks occurred at the same time but in different locations and with different subtypes of the Ebola virus.

– Sudan – Zaire

Ebola

– The total number of cases in these two outbreaks was 550 with 340 deaths.

– The case fatality rate from the Zaire subtype Ebola virus was 90 percent and case fatality rate for the Sudan subtype was 50 percent.

AIDS/HIV

• Background – The AIDS virus (Fig.7-5) belongs to a special

group of viruses known as retroviruses and is referred to as human immunodeficiency virus (HIV).

Fig. 7-5

AIDS/HIV

• Background – The AIDS virus almost exclusively focuses on

these white blood cells since these helper T cells have CD4 molecules on the surface to which the AIDS virus binds.

– The viral genetic information is then able to enter the cell and is transferred to the nucleus.

AIDS/HIV

• The Disease – HIV is transmitted most commonly by sexual

contact with an infected partner and can enter the body through the vaginal lining, vulva, penis, rectum or mouth.

AIDS/HIV

• The Disease – Since the virus appears in the blood and many

body fluids, it can be transmitted by infected blood as through contaminated needles.

– HIV has been transmitted to fetuses during pregnancy and birth.

AIDS/HIV

• The Disease – Many people remain asymptomatic for months

or years after acquiring the infection.

AIDS/HIV

• The Disease – Symptoms may emerge that include prolonged

enlargement of lymph nodes, energy and weight loss, recurrent sweating and fevers, skin rashes, or flaky skin, yeast infections, and pelvic inflammatory disease.

AIDS/HIV

• The Disease – The disease will often advance to a stage

referred to as AIDS or acquired immunodeficiency syndrome.

– Opportunistic infections produce a myriad of debilitating symptoms from respiratory distress, severe headaches, extreme fatigue, nausea, vomiting, to wasting and coma.

AIDS/HIV

• Epidemiology – A joint surveillance effort by UNAIDS and

WHO now estimates that over 30 million people are living with HIV infection at the end of 1997.

– This figure also includes over 1 million children under the age of fifteen.

AIDS/HIV

• Epidemiology – More than two-thirds of the total number of

people in the world living with HIV are from sub-Saharan Africa (Fig. 7-6).

Fig. 7-6Adapted from UNAIDS & WHO.108

Bacteria

• Escherichia coli – Background

• Gram negative, facultatively anaerobic, short straight rods that characteristically inhabit the intestines of humans and other animals and belong to the family Enterobacteriaceae.

Escherichia coli

• Background – Members of the enterics cause gastroenteritis,

mostly, but have also been implicated in urinary tract infections, wound infections, pneumonia, septicemia, and meningitis.

Escherichia coli

• Background – The strains of E. coli capable of causing

hemorrhagic colitis are referred to as Enterohemorrhagic Escherichia coli (EHEC).

Escherichia coli

• The Disease – Escherichia coli 0157:H7 is pathogenic for

humans and has characteristically produced bloody diarrhea with abdominal cramps; sometimes the infection causes nonbloody diarrhea with very few symptoms.

Escherichia coli

• The disease – Children under 5 years of age and the elderly,

the infection may progress into a more severe and life-threatening form of the disease known as hemolytic uremic syndrome (HUS).

– In the United States, HUS is the leading cause of acute kidney failure in children.

Escherichia coli

• Epidemiology – The majority of infections with serotype

0157:H7 have come from eating undercooked beef products, but many other sources of infection have been identified.

Escherichia coli

• Epidemiology – In 1993 a foodborne outbreak of serotype

O157:H7 was linked to the undercooked hamburgers eaten at a fast-food chain restaurant.

– The outbreak involved the infection of 700 persons from 4 different states with 51 of these persons developing HUS and four people dying from the syndrome.

Lyme Disease

• Background – Lyme disease is caused by the spirochete

Borrelia burgdorferi, a gram negative, slender, flexible bacteria that is helically coiled (Fig 7- 7).

Fig. 7-7

Lyme Disease

• Background – The organism is anaerobic and fermentative in

its energy metabolism and it is spread to humans by the bite of ticks of the genus Ixodes (Fig 7-8).

Fig. 7-8From the slide collection of Dr. John Edman, Entomology, Umass, Amherst

Lyme Disease

• Disease and Epidemiology – Lyme disease was first reported in 1975 near

Lyme, Connecticut, following a mysterious outbreak of arthritis.

Lyme Disease

• Disease and Epidemiology – The early stages of Lyme disease are

characterized by headache, fever, chills, swollen lymph glands, muscle and joint pain, and a characteristic skin rash (erythema migrans).

– Lyme disease rarely results in death but chronic Lyme disease can lead to permanent damage to joints or the nervous system.

Lyme Disease

• Disease and Epidemiology – Prevention is best accomplished by avoiding

tick-infested areas in the summer periods. – Spraying with DEET on exposed skin surfaces

other than the face will also be helpful.

Streptococcus

• Background – Streptococci are gram positive cocci (spheres)

arranged in chains or in pairs. – The major pathogens are included in groups A

and B, and their pathogenicity is associated with certain enzymes and surface proteins including hemolysins, erythrogenic toxins, and M-protein.

Streptococcus

• Background – Hemolysins are enzymes capable of breaking or

lysing blood cells. – The streptococci may produce a broad of array

of enzymes including neuraminidases, hyaluronidases, streptokinases, ATPases, DNAses, and many others that participate in the destruction and invasion of human tissue.

Streptococcus

• The Disease – The Group A Streptococci produce a variety of

diseases that include strep throat, impetigo, and scarlet fever.

– The more severe of these invasions results in necrotizing fasciitis and / or streptococcal toxic shock syndrome.

Streptococcus

• The Disease – Streptococcal toxic-shock syndrome (strep

TSS) is defined as any Group A streptococcal infection associated with the early onset of shock and organ failure.

Streptococcus

• Epidemiology – Beginning in the 1980s there has been a sudden

elevation in the reporting of a highly invasive group A streptococci infection with or without necrotizing fasciitis associated with shock and organ failure.

Streptococcus

• Epidemiology – The mortality rate for streptococcal TSS is

about 60 percent of the 2,000 to 3,000 cases reported per year.

– Annually, about 20 percent of the 500-1,500 patients who acquire Streptococcal fasciitis have died.

Tuberculosis

• Background and Disease – Tuberculosis (TB) is a chronic infectious

disease of the lower respiratory tract caused by Mycobacterium tuberculosis, a slender, acid- fast rod with cell walls containing high lipid levels.

– The slow growing bacilli are transmitted by aerosols from persons with active disease.

Tuberculosis

• Background and Disease – Symptoms normally begin to develop at this

stage from a cell mediated immunity that walls off the pathogen within multinucleated giant cells surrounded by lymphocytes and macrophages (Fig. 7-9).

Fig. 7-9

Tuberculosis

• Epidemiology – Tuberculosis kills over 3 million people

worldwide each year, and many more become ill from it.

– Tuberculosis was declared a U.S. public health emergency in 1992.

Tuberculosis

• Epidemiology – WHO estimates that the 1990's will see 90

million new cases and 30 million deaths with annual rates in infection in developing countries exceeding 2 percent.

Parasites

• Cryptosporidium – Background

• Cryptosporidium is a single celled microscopic protozoan parasite that belongs to the Class Sporozoa.

Cryptosporidium

• Background – The resistant form of the parasite is called an

oocyst which is characterized by an outer protective shell which protects the organism against environmental extremes such as heat, cold, dryness, and chemical insult.

Cryptosporidium

• Background – It is estimated that as few as 30 or even one

oocyst(s) may cause infection when swallowed. – Cryptosporidium is resistant to chlorine and

difficult to filter thereby making it a serious threat to water supplies.

Cryptosporidium

• Disease – The ingested oocysts reach the upper small

bowel where they excyst and produce four infectious sporozoites that attach to the surface epithelium of the digestive tract and reproduce, forming more oocysts and sporozoites.

Cryptosporidium

• Disease – The symptoms are self limiting, and include

watery diarrhea, stomach cramps, nausea, and a slight fever.

– The immunocompromised are at increased risk from infection, and may develop serious and life-threatening illness from this organism.

Cryptosporidium

• Epidemiology – There have been five major outbreaks

associated with public water supplies of Cryptosporidium gastroenteritis in the USA and seven in the UK since 1983.

Cryptosporidium

• Epidemiology – Contamination of drinking water by

Cryptosporidium is a growing concern especially after the outbreak in Milwaukee in 1993 which affected some 400,000 people.

Cryptosporidium

• Epidemiology – Cryptosporidium is found in animal droppings

and human feces, soil, drinking water and recreational water, food, hands, and surfaces contaminated by such wastes.

Malaria

• Background – Malarial diseases are caused by protozoan

parasites belonging to the genus Plasmodium. – There are four species known to infest humans

and they are: P. falciparum, P. vivax, P. ovale, and P. malariae.

Malaria

• Background – These parasites are transmitted from human to

human by the bite of a female anophelene mosquito in which the parasite has gone through a complex development cycle.

Malaria

• Background – A complex cycle takes place that involves the

union of the gametocytes in the stomach of the mosquito and results in the development of slender, microscopic sporozoites that appear in the salivary glands, and are infective for humans (Fig. 7-10a,b).

Fig. 7-10a

Fig. 7-10b

Malaria

• Background – Inside the cell, the parasite form the classical

signet ring stage (Fig. 7-11) and feed on the cells contents as they grow through the stages of trophozoites, and schizonts.

Fig. 7-11

Malaria

• Disease – The symptomology and pathogenesis of malaria

infection is related to the parasite's stage of growth and the host's parasitemia.

– High parasitemias result in decreased hemoglobin and a lower oxygen carrying capacity.

Malaria

• Disease – Untreated infections lead to splenomegaly

(enlarged spleen) and particularly in falciparum to cerebral malaria and death.

Malaria

• Epidemiology – The World health Organization (WHO)

estimates that there are 300 to 500 million people worldwide infected with malaria.

– The majority of malarial transmission occurs in tropical and subtropical countries (Fig 7-12).

Fig. 7-12Adapted from Zucker141

Malaria

• Re-emergence – Decreased spraying of homes with DDT – Drug resistant malaria – Global warming

Malaria

• Epidemiology – There have been 76 cases of malaria reported

from 1957 through 1994 including the three outbreaks occurring in the densely populated areas of New Jersey (1991), New York (1993) and Texas (1994).

PRACTICAL APPROACHES TO LIMITING THE EMERGENCE

OF INFECTIOUS DISEASE

– The emergence of 29 new infectious diseases and re-emergence of many others are creating national and international crises.

PRACTICAL APPROACHES TO LIMITING THE EMERGENCE

OF INFECTIOUS DISEASE

• A Prevention Strategy Plan for the United States was developed with four major goals: – (1) promptly investigate and monitor emerging

pathogens, the diseases they cause, and factors of emergence;

– (2) integrate laboratory science and epidemiology to optimize public health practice;

PRACTICAL APPROACHES TO LIMITING THE EMERGENCE

OF INFECTIOUS DISEASE – (3) enhance communication of public health

information about emerging diseases and ensure prompt implementation prevention strategies; and

– (4) strengthen local, state, and federal public health infrastructures to support surveillance and implement prevention and control programs.