Emerging and Reemerging Infectious Diseases and Pathogens

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Emerging and Reemerging Infectious Diseases and
Pathogens

• Lecture Week 13
• Medical Microbiology SBM 2044

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FIGURE 1. Leading causes of death worldwide.
About 15 million (gt25) of 57 million annual
deaths worldwide are the direct result of
infectious disease.
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Emerging infectious diseases

• CDC new, reemerging or drug-resistant infections
  whose incidence in humans has increased within
  the past three decades or whose incidence
  threatens to increase in the near future
• Infections that have newly appeared in a
  population or have existed previously but are
  rapidly increasing in incidence or geographic
  range (Morse 1995)

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• After great advances in medical research and
  antimicrobial drug discovery, technology
  development, improvement in sanitation..
• WHY are microbes still posing such a problem?

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Factors involved in the emergence of infectious
diseases

1. Unprecedented worldwide population growth,
   urbanization
2. Increased international travel
3. Increased worldwide transport, migration, and
   relocation of animals and food products
4. Changes in food processing, handling, and
   agricultural practices
5. Changes in human behaviour, technology and
   industry
6. Human encroachment on wilderness habitats that
   are reservoirs for insects and animals that
   harbour infectious agents

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Factors involved in the emergence of infectious
diseases

1. Microbial evolution and the development of
   resistance to antibiotics and other antimicrobial
   drugs
2. Changes in ecology and climate
3. Modern medicine (e.g. immunosuppression)
4. Inadequacy of public infrastructure and
   vaccination programs
5. Social unrest and civil wars
6. Bioterrorism
7. Virulence-enhancing mechanism of pathogens (the
   mobile bacteriophages, plasmids, transposons)

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• Emergence of infectious disease are the results
  from dynamic interactions between rapidly
  evolving infectious agents and changes in the
  environment and in host behaviour that provide
  such agents with favourable new ecological niches

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FIGURE 2. Global examples of emerging and
re-emerging infectious diseases.
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Classification of Emerging Infectious Diseases

• Newly emerging
• Have not previously been recognised in man
• Reemerging/resurging
• Existed in the past but are now rapidly
  increasing either in incidence or in geographical
  or human host range
• Deliberately emerging
• Microbes are those that have been developed by
  man, usually for nefarious use

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• Newly emerging infections
• Have not previously been recognised in man

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AIDS model

• AIDS have affected gt 60 million people worldwide
• jumping to humans species, may be a consequence
  of the consumption of bush meat from non-human
  primates
• this allow HIV-1 and HIV-2 to evolve in host
• emergence is amplified by disruptions in the
  economic and social infrastructure in
  post-colonial sub-Saharan Africa
• urban poverty, a weakening of family structure
  all promoted promiscuous sexual practices, and
  increased travel.

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Dead-end transmission of zoonotic and
vector-borne diseases

• Arenavirus haemorrhagic fevers (inc Lassa fever)
  and hantavirus pulmonary syndrome (HPS)
• viruses in these groups have co-evolved with
  specific rodent species
• increased human-rodent contact as a result of
  modern environmental factors farming, keeping
  domestic pets, hunting and camping, deforestation
• Malaysian Nipah virus epidemic 1998-1999
• pigs crammed together in pens located in or near
  orchards, attracted fruit bats which are the
  natural hosts of the Nipah and Hendra viruses
• virus aerosolisation caused infection of pigs
• Overcrowding results in viral transmission to pig
  handlers

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Other newly emerging agents

• Environmentally persistent organisms
• Legionnaires caused by Legionella pneumophila due
  to the use of air-con
• Campylobacter jejuni, Shiga-toxin-producing E.
  coli infect agricultural animals
• enter through food, milk, water or direct contact
• Microbial agents and chronic diseases
• Chronic liver damage, hepatocellular carcinoma -
  Hep B and C
• Cervical cancer papillomaviruses
• Burkitts lymphoma Epstein-Barr virus
• Gastric ulcers and gastric cancer

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• Re-emerging and Resurging Infections
• Existed in the past but are now rapidly
  increasing either in incidence or in geographical
  or human host range

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Geographical spread of infections

• Depend on the rate and degree to which they
  spread across geographical areas
• the movement of human hosts/vectors/ reservoirs
  of infections
• 1933 commercial air travel
• 1981 pandemic spread of acute haemorrhagic
  conjunctivitis
• Epidemics of meningococcal meningitis during the
  Hajj
• Epidemic SARS (a newly emerging disease) from
  China to elsewhere worldwide

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FIGURE 3. Probable cases of severe acute
respiratory syndrome (SARS) with onset of illness
from 1 November 2002 to 31 July 2003.
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FIGURE 4 The severe acute respiratory syndrome
(SARS) pandemic and important findings.
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FIGURE 5 Schematic representation of the severe
acute respiratory syndrome coronavirus (SARS-CoV)
particle.
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Infectious agents

• Malaria
• Plasmodium falciparum was thought to be
  eradicated because of the effective use of DDT
  insecticide
• But mosquito gain resistance
• Tuberculosis
• Isoniazid was initially effective to cure TB
• By 1980s, the era of HIV/AIDS, increased immune
  deficiencies of people, increases the risk of
  latent M. tuberculosis
• Also the fact that TB is a disease of poverty
  crowding, inadequate hygiene
• Staphylococcus aureus
• Drug-resistant organism
• Sulpha drugs 1940s ? penicillin 1950s ?
  methicillin 1980s ? vancomycin 2002

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Re-emerging vector-borne diseases

• Flavivirus which caused dengue
• vector Aedes aegypti mosquitoes
• 2001-2002 epidemic in Hawaii
• dengue has recently been transmitted by Aedes
  albopictus, which spreads into areas where A.
  aegypti are not found and persisting for longer
  seasonal periods

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Influenza A

• Was known as endemic gastrointestinal viruses of
  wild waterfowl, now has jump species into
  domestic fowl, farm animals and humans
• Antigenic changes in haemagglutinin and
  neurominidase glycoproteins shifts (major
  antigenic changes in HA or NA)
• Deadly pandemics has occurred in 1888, 1918, 1957
  and 1968

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FIGURE 6. Documented human infections with avian
influenza viruses, 19972004.
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Infectious diseases on the rise

• Global spread of AIDS
• Resurgence of tuberculosis
• Appearance of new enemies (hantavirus, pulmonary
  syndrome, hepatitis C and E, Ebola virus, Lyme
  disease, cryptosporidiosis and E. coli O157H7
• Bird flu which attacks the Southeast Asia
• Prion disease of Creutzfeldt-Jakob disease
• Antibiotic resistance Staphylococcus bacteria
• Several major multistate foodborne outbreaks
• A new strain of drug resistance tuberculosis

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FIGURE 7 Generic model of the organization of a
rapid research response to an emerging infectious
disease.
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Reference

• Morens DM, Folkers GK and Fauci AS (2004) The
  challenge of emerging and re-emerging infectious
  diseases. Nature 430 242-249.
• Prescott. Chapter
• Brooks Chapter 29 pages 390-391 only.
• Emerging and Re-emerging Infectious Diseases the
  Perpetual Challenge http//www.milbank.org/repor
  ts/0601fauci/0601fauci.html