Lecture 9: Reemerging Infectious Diseases Overview

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Lecture 9 Re-emerging Infectious
DiseasesOverview

• ANTIBIOTIC RESISTANT BACTERIA
• MALARIA
• YELLOW FEVER
• TUBERCULOSIS
• CHOLERA
• BUBONIC PLAGUE
• SUMMARY

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Antibiotic Resistant Bacteria (1)

• The discovery of penicillin in 1928 and the
  introduction of other antibiotics such as
  streptomycin, chloramphenicol, tetracycline in
  the 1940s raised hopes that cures could be found
  for all infectious diseases.
• Only one family of antibiotics (quinolones) have
  been developed since the 1960s.
• Strains of Staphylococcus aureus developed
  immunity against penicillin in the 1960s.
  However, methicillin was still effective.
• Methicillin resistant Staphylococcus aureus
  (MRSA) were found by the 1980s. Vancomycin was
  used as a last resort.
• Now vancomycin resistant Staphylococcus aureus
  (VRSA) has been observed in hospitals around the
  world.

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Antibiotic Resistant Bacteria (2)

• Streptococcus A which caused scarlet fever more
  or less vanished by the 1960s, but it re-emerged
  in a much more deadly form in the late 1980s.
• Streptoccous pyrogenes (dubbed the flesh eating
  bug) causes life threatening necrotizing
  fascitis unless stopped by amputation.
• Various strains of Pneumonoccus have resistance
  to whole classes of antibiotics.
• Hospitals are a major breeding ground for
  antibiotic resistant bacteria.

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Malaria

• Resistance to chloroquine was noticed in southern
  Asia in the 1950s. By the 1960s some strains of
  Plasmodium falciparum had developed resistance to
  the 4 main anti-malarial drugs.
• A new drug, mefloquine, was adopted in the 1970s,
  but resistant strains of falciparum emerged by
  the 1980s.
• Strains of falciparum in Thailand have evolved an
  enzyme which expels all hostile chemicals, making
  it resistant to drugs that have not even been
  invented.

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Yellow Fever

• Yellow fever is transmitted by Aedes aegypti (a
  mosquito). The reservoir is capuchin and rhesus
  monkeys.
• Yellow fever was formerly a jungle disease, but
  it is now endemic in Latin American cities.
• The mosquito is actually more common in North
  America, prompting fears that yellow fever could
  become endemic there was a sufficient reservoir
  of infection.

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Tuberculosis

• Tuberculosis has been on the increase since the
  1980s. It is the main cause of death worldwide.
• Many people carry the bacillus but do not develop
  symptoms unless their immune system is
  compromised.
• The resurgence in tuberculosis is associated with
  HIV infection.
• The problem is compounded by the emergence of
  drug resistant strains, partly due to
  HIV-infected drug users not completing antibiotic
  courses.

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Cholera

• There were no new pandemics for most of the 20th
  century, but the 7th pandemic began in the 1960s
  (the El Tor strain). It spread to Latin America
  in the 1980s. Developed countries have so far
  escaped.
• An even more virulent strain (0139) has emerged
  in the Sea of Bengal. This may be the beginnings
  of 8th pandemic. There is no guarantee that
  developed countries will escape.

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Bubonic Plague

• Bubonic plague was introduced into the Chinese
  community in San Francisco at the beginning of
  the 20th century. Since then it has been moving
  underground eastwards in infected ground
  squirrels and prairie dogs. So far few humans
  have been infected.
• A bubonic plague epidemic in India in 1994
  infected 2,500. Fortunately it had low virulence
  and was amenable to tetracycline.

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Conclusion

• The re-emerging old infectious diseases have made
  relatively little impact upon the public
  imagination in DCs because either they affect
  only a small number of people, many of whom are
  already sick or poor (e.g. MRSA or TB), or else
  they are 'out there' in the Third World where
  'life is cheap' and 'these things happen'.
• However, given the rapid development of
  drug-resistant strains, coupled with rapid air
  transportation, it may be only a matter of time
  before one of our ghosts from the past come back
  to haunt us.