Public Health 150
Contemporary Issues in Public Health
Emerging Infectious Diseases
Robert Kim-Farley, MD, MPH
15 October 2003
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Infectious disease is one of the few genuine
adventures left in the world. The dragons are all
dead and the lance grows rusty in the chimney corner
. . . About the only sporting proposition that remains
unimpaired by the relentless domestication of a once
free-living human species is the war against those
ferocious little fellow creatures, which lurk in the dark
corners and stalk us in the bodies of rats, mice and
all kinds of domestic animals; which fly and crawl
with the insects, and waylay us in our food and drink
and even in our love.
- (Hans Zinsser,1934 quoted in Murphy 1994)
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CONTROL AND PREVENTION
PROGRAMS

Public heath planning for the control of
infectious diseases must consider a number of
factors to design optimal, rationally based
control and prevention programs, including:
 the risk of disease;
 the magnitude of disease burden (as
measured by mortality, degree of disability,
morbidity, and economic costs);
 the feasibility of control strategies;
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CONTROL AND PREVENTION
PROGRAMS (continued)




the cost of control measures;
the effectiveness of such measures (on
current levels of disease and impact on future
cases or outbreaks);
the adverse effects or complications of the
control measures; and
the availability of resources.
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Risk and Magnitude of Diseases


The tools of disease surveillance for recognition and
evaluation of the patterns of disease can provide the
information on the risk and magnitude of disease burden
to individuals, persons in institutions, subgroups of
populations, and the community at large.
Establishment and maintenance of the infrastructure for
surveillance, including a system for the reporting of
notifiable infectious diseases and unusual events, must
be a high priority. Unusual events, like with SARS, may
portend new and emerging diseases.
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Feasibility of Control

Feasibility of possible control and
prevention strategies must be assessed
through operational research, pilot
projects or from field experience.

The fact that a particular measure can help
control a disease does not mean it can be
applied on a sufficient scale to have the
desired impact.
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Cost of Control

The cost of control activities (in both
manpower and materiel) can be assessed
through costing studies.

A costly measure, even if it provides a high
degree of control for an infectious disease,
may not be affordable to the society or
reasonable to apply in the light of other less
expensive alternative strategies.
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Effectiveness of Control Measures

Effectiveness of control measures may be
assessed through epidemiologic studies to
find out their impact on reduction in the
incidence or prevalence of disease.
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Availability of Resources


The availability of resources for preventive and
control programs forces public health planners
to set priorities by taking into account all these
factors and then designing programs that have
maximum impact within available resources.
Planners have a responsibility to mobilize
additional necessary resources by raising public
awareness and generating political will.
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Availability of Resources
(continued)


Effective communication of disease burden
and the results achievable through wellmanaged and effective control programs
can be a powerful tool for advocacy.
Ideally, communities should actively
participate in the planning, execution, and
evaluation of public health programs.
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International Migration


The situation of international migration of
many persons in the world today presents an
additional complexity to the design of programs
for the control of infectious diseases, especially
emerging infectious diseases.
Pertinent issues include:



refugee camps,
legal status of migrants in recipient countries, and
temporary return migration.
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International Commerce and
Transportation

International commerce and
transportation are specific areas of
concern for public health infectious
disease control programs and emerging
diseases, especially as the speed of travel
has increased.
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International Commerce and
Transportation (continued)

The tools of control include such measures
as:


spraying insecticides effective against
mosquito vectors of malaria in aircraft before
departure, in transit, or on arrival; and
rat-proofing or periodic fumigation to control
rats on ships, docks, and warehouses to
prevent plague.
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International Commerce and
Transportation (continued)

Specific international control measures
relating to aircraft, ships, and land
transportation for infectious diseases have
been specified in the WHO International
health regulations.
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EMERGING INFECTIOUS
DISEASES
Microbes and vectors swim in the evolutionary
stream, and they swim faster than we do.
Bacteria reproduce every 30 minutes. For them,
a millennium is compressed into a fortnight.
They are fleet afoot, and the pace of our
research must keep up with them, or they will
overtake us. Microbes were here on earth 2
billion years before humans arrived, learning
every trick for survival, and it is likely that they
will be here 2 billion years after we depart
(Krause 1998).
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Factors contributing to emergence or
re-emergence of infectious diseases


Human demographic change by which
persons begin to live in previously uninhabited
remote areas of the world and are exposed to
new environmental sources of infectious agents,
insects and animals.
Breakdowns of sanitary and other public
health measures in overcrowded cities and in
situations of civil unrest and war.
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Factors contributing to emergence or
re-emergence of infectious diseases
(continued)


Economic development and changes in the
use of land, including deforestation,
reforestation, and urbanization.
Other human behaviors, such as increased
use of child-care facilities, sexual and drug use
behaviors, and patterns of outdoor recreation.
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Factors contributing to emergence or
re-emergence of infectious diseases
(continued)


International travel and commerce
that quickly transport people and goods
vast distances.
Changes in food processing and
handling, including foods prepared from
many different individual animals and
transported great distances.
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Factors contributing to emergence or
re-emergence of infectious diseases
(continued)


Evolution of pathogenic infectious agents
by which they may infect new hosts, produce
toxins, or adapt by responding to changes in the
host immunity.
Development of resistance of infectious
agents such as Mycobacterium tuberculosis and
Neisseria gonorrhoeae to chemoprophylactic or
chemotherapeutic medicines.
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Factors contributing to emergence or
re-emergence of infectious diseases
(continued)


Resistance of the vectors of vectorborne infectious diseases to pesticides.
Immunosuppression of persons due
to medical treatments or new diseases
that result in infectious diseases caused by
agents not usually pathogenic in healthy
hosts.
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Factors contributing to emergence or
re-emergence of infectious diseases
(continued)


Deterioration in surveillance systems for
infectious diseases, including laboratory support,
to detect new or emerging disease problems at
an early stage.
Antimicrobial drug resistance as a major
factor in the emergence and re-emergence of
infectious diseases deserves special attention.
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Factors contributing to emergence or
re-emergence of infectious diseases
(continued)

Biowarfare/bioterrorism: An
unfortunate potential source of a new or
emerging disease threat.
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Examples of emerging infectious
disease threats

Toxic shock syndrome, due to the
infectious toxin-producing strains of
Staphylococcus aureus, illustrates how a
new technology yielding a new product,
super-absorbent tampons, can create the
circumstances favoring the emergence of
a new infectious disease threat.
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Examples of emerging infectious
disease threats (continued)

Lyme disease, due to the infectious
spirochete Borrelia burgdorferi, illustrates
how changes in the ecology, including
reforestation, increasing deer populations,
and suburban migration of the population,
can result in the emergence of a new
microbial threat that has now become the
most prevalent vector-borne disease in the
United States.
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Examples of emerging infectious
disease threats (continued)

Shigellosis, giardiasis, and hepatitis A are
examples of emerging diseases that have
become threats to staff and children in
child-care centers as the use of such
centers has increased due to changes in
the work patterns of societies.
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Examples of emerging infectious
disease threats (continued)

Opportunistic infections, such as pneumocystis
pneumonia caused by Pneumocystis carinii,
chronic cryptosporidiosis caused by
Cryptosporidium species, and disseminated
cytomegalovirus infections, illustrate emerging
disease threats to the increasing number of
persons who are immunosuppressed because of
cancer chemotherapy, organ transplantation, or
HIV infection.
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Examples of emerging infectious
disease threats (continued)

Foodborne infections such as diarrhea caused by
the enterohemorrhagic strain 0157:H7 of
Escherichia coli and waterborne infections such
as gastrointestinal disease due to
Cryptosporidium species are examples of
emerging disease threats that have arisen due
to such factors as changes in diet, food
processing, globalization of the food supply and
contamination of municipal water supplies.
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Examples of emerging infectious
disease threats (continued)

Hantavirus pulmonary syndrome first
detected in the USA in 1993 and caused
by a previously unrecognized hantavirus
illustrates how exposure to certain kinds
of infected rodents can result in an
emerging infectious disease.
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Examples of emerging infectious
disease threats (continued)

Nipah virus disease first detected in
Malaysia in 1999 and caused by a
previously unrecognised Hendra-like virus
demonstrates how close contact with pigs
can result in an emerging infectious
disease.
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Examples of emerging infectious
disease threats (continued)

Emergence of the new toxigenic Vibrio
cholerae O139 strain of cholera in Asia is
an example of a new strain of an
infectious agent for which there is no
protection from prior infection with other
strains or with current vaccines and for
which previous standard diagnostic tests
are ineffective.
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Examples of emerging infectious
disease threats (continued)

SARS is the most recent example of how
devastating a newly emerging disease can
be in terms of economic impact and how,
in the absence of vaccines,
chemoprophylaxis, or chemotherapy “old”
measures of quarantine and isolation may
be the only “tools” we in public health
have to combat disease.
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Final thoughts

It is only through worldwide concerted
action will the effort to control infectious
disease be effective (analogy).
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Final thoughts (continued)

We have now entered an era where, as
Nobel Laureate Dr. Joshua Lederberg has
stated, “The microbe that felled one child
in a distant continent yesterday can reach
yours today and seed a global pandemic
tomorrow”
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