Public Health 150 Contemporary Issues in Public Health

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Public Health 150Contemporary Issues in Public
Health

• Emerging Infectious Diseases
• Robert Kim-Farley, MD, MPH

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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 well-managed 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 vector-borne
  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 0157H7 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