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MICR 454L
Emerging and Re-Emerging
Infectious Diseases
Lecture 1: Identifying the Problem
Dr. Nancy McQueen & Dr. Edith Porter
Overview – the course
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Course requirements and challenge for the
students
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Quizzes
Midterm
Research paper presentation and discussions
Hot topics presentations
Case studies
Comprehensive final exam
The Problem:
Emerging
and Reemerging
Infectious
diseases
Overview – the problem
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Identifying the problem
Factors responsible for emerging infections
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World population growth
Urbanization
Ecological disturbances
Technological advances
Microbial evolution and adaptation
Human behavior and attitudes
The problem of emerging
infections
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The problem is a worldwide challenge by microbes
whose survival is linked to ours

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The vast majority of microbes are beneficial
The small minority of microbes that produce disease are called
pathogens.
History of the problem
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From the 1950’s through the 1970’s microbial diseases appeared
to be on their way out
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Vaccinations
Antibiotics and other antimicrobics
Improved world economy and decreased poverty
However, from 1980 to 1992 the CDC reported a 22% increase
(excluding AIDS) in infectious diseases
The problem of emerging
infections
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Emerging infections are defined as those infections whose incidence
in humans has increased in the past two decades or will increase in
the future.
Emerging infections can be defined as
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In 1996, published data indicated that since 1980 there was a
greater than 50% increase in deaths caused by microbes in the
United States.
New
Reemerging
Drug resistant infections
Emergence is a two step process

Introduction of the infectious agent into a new population. The agent
may be:
 Already present



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Located within another species
A variant of an existing pathogen
Dissemination of the infectious agent
What are some of these emerging infections?
Emerging and Re-emerging
Infectious Diseases
avian
Red names are newly emerging infectious diseases; Blue names are re-emerging infectious diseases; Black
names are emerging bioterrorism infectious diseases; Names circled in green are RNA viruses
Adapted from Morens, D. M., et al. 2004. The Challenge of Emerging and Re-emerging Infectious
Diseases. Nature 430: 242-249
Recent outbreaks of infectious
diseases
Leading causes of death
Leading causes of death
6%
9%
Infectious diseases
25%
5%
Cardiovascular diseases
Cancers
Injuries
11%
Maternal complications
13%
Respiratory and Digestive
diseases
31%
Other
Leading causes of death,1998. There were 53.9 million deaths world-wide
in 1998. Cancers, cardiovascular, and respiratory and digestive diseases
can also be caused by infections. Thus , the percentage of deaths due to
infectious diseases may be even higher than shown. (Source: WHO report,
1999.)
Leading causes of death in
Africa versus the Americas
Africa 2002: 10.7 million deaths
2%
5%
2%
7%
Infections
Cardiovascular
7%
Cancers
Injuries
4%
Maternal and perinatal
Respiratory
63%
10%
Intentional
Other
The Americas 2002: 6 million deaths
11%
14%
Infectious
4%
Cardiovascular
2%
Cancers
Injuries
7%
32%
4%
Maternal and perinatal
Respiratory
Intentional
Diabetes
7%
Other
19%
Causes of death in the Americas and
Africa, 2002, by percentage of
cause.There were 10.7 million deaths in
Africa, 6.7 million due to infectious
diseases. There were 6 million deaths
in the Americas, 623,000 due to
infectious diseases. Intentional deaths
include murder suicide, and war.
Leading infections disease
killers
Leading infectious disease killers
4
Deaths in millions
3.5
3
2.5
Over age 5
2
Under age 5
1.5
1
0.5
0
Acute
respiratory
infection
AIDS
DiarrhealTuberculosis Malaria
diseases
Measles
Leading infectious killers. The graph shows millions of deaths world-wide in
1998 for persons of all ages. Pneumonia and influenza are included in acute
respiratory infections. Deaths among HIV-positive individuals with tuberculosis
are included under AIDS. (Source: WHO report, 1999.
Factors responsible for
emerging diseases
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World population growth – most important
Urbanization (changes in demographics)
Ecological disturbances
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Technical advances
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Air travel
Unsafe blood supplies
Human behavior and attitudes
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Deforestation – disturbances to natural habitat
Climate changes
Natural disasters (drought, flooding)
Complacency
Migration
Societal factors
Microbial evolution and adaptation
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Antimicrobial resistance
Evasive strategies
World population growth
10
9
8
7
6
5
4
3
2
1
0
19
45
19
55
19
65
19
75
19
85
19
95
20
05
20
15
20
25
20
35
20
45
Population (in billions)
World Population Growth
Year
World population, 1950 to 2050. Projections are based
on an estimated annual growth rate of 1.25%. (Source:
U.S. Census Bureau, International Dada Base, May 10,
2000.
World population growth is
central to the issue
Increased
urbanization
Changes in
human behavior
and activities
Technological
advances
Population growth
Increased transmission
Ecological
disturbances
Advances in
biology and
medicine
How does increased population result
in an increase of infectious diseases?
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Increased transmission
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Population density
 Person to person transmission is facilitated by population
density increases
Distribution of the population
 The elderly are more susceptible to disease and can serve
as a source of infection
Other potential effects:
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Greater likelihood of global warming
Larger numbers of travelers
More frequent wars
Increased numbers of refugees and internally displaced
persons
How does increased population result
in an increase of infectious diseases?
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Increased hunger and malnutrition
More crowded living in urban slums
Increased numbers of people living in poverty
Inadequate potable water supply
More large dam construction and irrigation
projects
Urbanization
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In the past 50 years, about 25% of the
population have left their rural environment for
the cities
By 2030, more than 75% of the world’s
population will live in cities
Urbanization
Percent of world
population living in cities
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5
billion
70
60
2.5
billion
50
750
million
40
30
20
240
million
10
0
1900
1950
1995
2030
Year
Progressive urbanization of out planet. The different colors for 2030
indicate proportions of urban population that are projected to live in
developed countries (20%) and underdeveloped countries (80%)
Urbanization
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The magnitude of the effect of urbanization
on infectious diseases depends upon:
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Economy of the country
Public health infrastructure necessary to cope
with the increasing population density
Urbanization and poverty
Drain on natural
resources and
increased pollution
Decreased public
Malnutrition
health infrastructure
and decreased and
*Sanitation
health services
*Rodent increase
*Immunization
Increased infectious diseases
Slums and shanty towns.
Poverty is associated with a
lack of sanitary facilities, an
increase in rodent populations,
a lack of safe drinking water,
and other circumstances that
contribute to infectious
diseases
Urbanization
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Emergence of diseases due to urbanization
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Dengue fever – is caused by a flavivirus
 Causes Dengue fever and Dengue hemorrhagic fever
 Is transmitted by Aedes mosquitoes that are unable to fly
long distances
 House–to-house infestation of the mosquito occurs in
cramped urban living conditions
 Disease has moved into the U.S. as the virus infects a
different species of Aedes mosquito
West Nile virus – is also caused by a flavivirus
 Is also transmitted by a mosquito vector
 First identified in the U.S. in New York City in 1999.
Spread of WNV in the United States
Even in developed countries urbanization
often leads to poverty and disease
Ecological disturbances
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Deforestation
Deforestation. As people move into and/or develop agriculture in areas
that were formerly forests, there is increased contact with animals,
including insects, that harbor infectious microbes. In search of food, the
displaced animals return to neighborhoods that were once their lands.
Ecological disturbances
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Deforestation
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Eastern U.S.
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Lyme, Connecticut in 1970’s
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Indigenous mammals displaced Kissing bugs feeding on
humans  Chagas disease
Aswan High Dam in Egypt
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Humans in contact with excretions of infected rodents  
Venezuelan hemorrhagic fever
Central railroad in Brazil
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Intersection of humans with rodent-deer life cycle of B.
burgdorferi infected ticks  emergence of Lyme disease
Guanarito region of central Venezuela
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Raccoons foraging for food  rabies (zoonotic disease transmitted from animal to human)
New snail habitat  schistosomiasis
Aswan High Dam in Egypt
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Flood lands  Mosquitoes  Rift valley fever
Ecological disturbances Deforestation
A village with a high incidence of
leishmaniasis. Leishmaniasis is a
protozoan infection transmitted by infected
sand flies. Sand flies are poor fliers, but
they can traverse the short distance from
their forest habitat.
Leishmania
Deforestation
The interspecies leap.
AIDS, which originated in
Africa, is presumed to have
jumped the species barrier
from infected monkeys to
humans.
HIV
Ecological disturbances
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Climatic changes including global warming may
favor the outbreak of many infectious diseases:
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Vibrio parahaemolyticus - ocean borne
Malaria - mosquitoes
Rift Valley fever - mosquitoes
Hantavirus - mice
Cholera - waterborne
Hepatitis - waterborne
Lyme disease - ticks
Dengue fever - mosquitoes
Cryptosporidosis - waterborne
Ecological disturbances
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Climatic changes are likely to particularly effect vectorborne diseases (diseases carried to humans by
arthropods)
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May effect the vector
May effect the microbe
Disease
Malaria
Population at risk,
millions
Prevalence of infection
Present distribution
Possible change of
distribution as a result
of climatic change
2,100
270 million
Tropics, subtropics
Highly likely
Lymphatic filariasis
900
90.2 million
Tropics, subtropics
Likely
Onchocersiasis
90
17.8 million
Africa, Latin America
Likely
Schistosomiasis
600
200 million
Tropics, subtropics
African
trypanosomiasis
50
25,000 new cases per year
Leishmaniasis
350
12 million infected + 400,000
new cases per year
Dracunculiasis
63
1 million
Dengue
NA
NA
Tropics, subtropics
Yellow fever
NA
NA
Africa, Latin America
Likely
Japanese
encephalitis
NA
NA
East and Southeast
Asia
Likely
Other arboviral
diseases
NA
NA
Tropical to temperate
zones
Likely
Tropical Africa
Asia, Southern Europe,
Africa, South America
Tropics (Africa, Asia)
Very likely
Likely
Not known
Unlikely
Arboviral diseases
Very likely
Ecological disturbances
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Natural disasters
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Flooding malaria and cholera in Africa
Drought  famine  disease in Africa
Increased humidity crop of pine needles
mouse deer populationemerging Hantavirus
infections in Four Corners area of U.S.
Technological advances
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International travel – SARS, penicillin-resistant
gonorrhea, monkeypox
Approximate flying time from New York City
Sydney, Australia: 22 hours (1 stop)
Tokyo, Japan: 14 hours (nonstop)
Tel Aviv, Israel: 10 hours (nonstop)
Nairobi, Kenya: 16 hours (1 stop)
Incubation period for selected diseases
Whooping cough: 7-10 days
Gonorrhea: 2-6 days
Salmonella food poisoning: 8-48 hours
Ebola fever: 4-16 days
Measles: 12-32 days
Chicken pox: 10-23 days
It’s a small world after all. In a span of a couple of days, President Bill
Clinton demonstrated the truth of this cliché. He flew from Washington to
New York and back. Then he flew to Cincinnati, Denver, and Aspen. After
briefly returning to Washington again, he flew to Morocco. From there he
returned to Washington one more time. All that travel took place in one
weekend.
Technological advances
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Blood transfusions - hepatitis, HIV, malaria,
trypanosomiasis, syphilis, Chaga’s disease.
Organ transplants and immunosuppressive
drugs - CMV,
mad cow disease
Microbial evolution and
adaptation
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Antimicrobic resistance
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In the last 50 years antibiotics and antimicrobics
have saved the lives of innumerable individuals
with infections
However now the microbes are becomimg
resistant to antimicrobics - why?
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GROSS MISUSE of antimicrobics
Microbial evolution and
adaptation
• Development of antimicrobic resistance:
Developing countries
Developed countries
Insufficient use of antimicrobics
Overuse of antimicrobics
Too expensive
Available virtually on demand
Save it for a rainy day
Used when not necessary
Failure to complete dose
Failure to complete dose
Antimicrobic resistance
Emergence of antimicrobial
drug resistant bacteria
Increasing resistance of
selected pathogens
Methicillin resistant
Staphylococcus aureus
Microbial evolution and
adaptation
Examples of drug-resistant diseases:
Bacterial disease Viral disease
Protozoan disease
Typhoid fever
HIV infection
Malaria
Tuberculosis
Hepatitis B
Visceral leishmaniasis
Gonorrhea
Staphylococcal infection
Shigellosis
Pneumococcal infection
Enterococcal infection
Microbial evolution and
adaptation
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Microbes change their surface structures to
evade host defenses – Vibrio cholera
Antibody can
bind to antigen
Antibody can’t
bind to antigen
Changing one’s coat. Trypanosomes and other
microorganiams can form new surface antigens not recognized
by antibodies. This is an important evasion strategy.
Microbial evolution and
adaptation
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Acquisition of new proteins introduced by lysogenic
bacteriophages
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Mutations and evolution of viruses.
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Toxins produced by Streptococcus pyogenes that lead to
necrotizing fasciitis (flesh eating bacteria).
Mainly RNA viruses
 Include Ebola virus, SARS virus, Hantavirus, Avian
influenza virus
More on this later
Adaptation of insect vectors
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Mosquitoes become resistant to DTT
 Malaria
 ? West Nile virus
Human behavior and attitudes
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Complacency - “it can’t happen to me”
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Return to risky sexual behavior and AIDS and
gonorrhea
Failure to immunize your children - measles
Failure to get immunizations when traveling to
foreign countries - yellow fever and malaria
Human behavior and attitudes
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Human migration -wars and conflicts resulting
from political differences result in refugees or
internally displaced persons who move from
one part of the country to another
A refuge camp. Refuge camps are hotbeds
of infection. Crowding and lack of hygiene
and sanitation favor the incidence and
transmission of disease
Human behavior and attitudes
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Societal factors
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Increased numbers of women workers in child care
centers
 Intestinal parasites
 Diarrhea
 Middle ear infections
Meningitis
Increased longevitynursing homes, day care centers for
adults, and assisted living environments
Food production and dietary habits lead to  food-borne
diseases
 Centralized food processing –E. coli from spinach
 Fast food and take-out restaurants
 Import of agricultural produce - hepatitis A from
strawberries and onions from Mexico, Cyclospora
from Guatamalan raspberries
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Human behavior and attitudes
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Tattooing and body piercing and
Staphylococcus aureus infections:
Tattooing and skin piercing. Tattooing
and skin piercing are a risky part of
popular culture. The skin is invaded,
potentially resulting in serious infection
because of he use of unclean instruments
Take Home Message
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Infectious disease deaths decreased from the 1950s
through the 1970s.
Infectious disease deaths started to rise again in the
1980s.
New, emerging, and reemerging infections are a major
health problem today.
The world population growth is central to the issue of
emerging infections. Other contributing factors include:


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Urbanization
Ecological disturbances
Technological advances
Microbial evolution and adaptation
Human behavior and attitudes
Resources
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The Microbial Challenge, by Krasner, ASM Press,
Washington DC, 2002.
Brock Biology of Microorganisms, by Madigan and
Martinko, Pearson Prentice Hall, Upper Saddle
River, NJ, 11th ed, 2006.
Microbiology: An Introduction, by Tortora, Funke and
Case; Pearson Prentice Hall; 9th ed, 2007.
Emerging Infectious Diseases. Michael A. Palladino,
series editor; Benjamin Cummings speical topics in
biology, 2006.