Lecture 18 : ReEmerging Infectious Diseases Overview

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Lecture 18 Re-Emerging Infectious
DiseasesOverview

• ANTIBIOTIC RESISTANT BACTERIA
• Staphylococcus aureus
• Streptococci pyrogenes
• Pneumonoccus
• Enterococcus faecium
• Clostridium difficile
• RE-EMERGING DISEASES
• Malaria
• Tuberculosis
• Yellow Fever
• Cholera
• Bubonic Plague

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Staphlyococcus aureus
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Staphylococcus Aureus

• Staphylococcus aureus is very common, but also
  very deadly if it gets into the blood stream.
• It was formerly a major cause of death following
  surgery.
• Penicillin proved to be very effective.
• When penicillin began to fail in 1950s,
  methicillin proved effective.
• Methicillin resistant strains were identified in
  1961 but did not become common until the 1990s
  (MRSA).
• Vancomycin was an effective drug of last resort,
  but VRSA was reported in the late 1990s.
• About 2 billion people worldwide carry Staph A.
  and about 50 million carry MRSA.

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Streptococcus pyrogenes
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Streptococcus Pyrogenes

• Streptoccus pyrogenes was cause of scarlet fever,
  rheumatic fever, and puerperal fever but more or
  less vanished by 1960.
• Displaced by Strep B.
• Reappeared in 1989. Causes necrotizing fasciitis
  the flesh eating bug. Can only be stopped by
  amputation.
• Still susceptible to penicillin, but resistant to
  macrolides (e.g. Erythromycin).

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Streptococcus pneumoniae
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Other Resistant Bacteria

• Penicillin resistant Pneumococcus was discovered
  in Spain in 1980s. Became resistant to
  cephalosporin antibiotics in US in 1990s. Still
  responds to vancomycin.
• Enterococcus faecium developed a Vancomycin
  resistant form (VRE) in 1989. It is now resistant
  to all antibiotics.
• Severe diarrhoea in patients on antibiotics
  caused by Clostridium difficile. At least two
  fatal epidemics in the community. Developing
  resistance to quinolones.
• Broad-spectrum antibiotics may also kill
  commensals (i.e. beneficial bacteria) which help
  keep the pathogenic bacteria in check (e.g.
  Candida albicans).

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Clostridium difficile
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Synopsis

• Drug resistent bacteria in the developed world
  mostly evolved in hospitals
• Antibiotics
• Immune compromised patients
• Cutbacks in hospital spending.
• Although still largely confined to hospitals,
  there have been several outbreaks in communities.
  
• They now kill more Americans than AIDS and breast
  cancer combined.

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Re-Emerging Infectious Diseases

• Most of the victims of antibiotic resistent
  bacteria in developed countries are sick people
  in hospitals.
• Some infectious diseases that strike down
  otherwise healthy people in the general
  population are also posing a renewed threat for
  similar reasons.
• However, the impact is mostly (although not
  exclusively) felt in the Third World.

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Malaria

• US-funded global campaign 1958-63. Outcry against
  DDT following Rachel Carsons Silent Spring.
• Mosquitoes developed resistance to DDT used in
  agriculture in Third World countries.
• 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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Tuberculosis(1)

• Tuberculosis caused 1 billion deaths in 19th and
  20th centuries.
• Declined in developed countries, but it has been
  on the increase since the 1980s. It is the main
  pathogenic 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.
• Once they develop symptoms, they can infect other
  people.

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Tuberculosis(2)

• The problem is compounded by the emergence of
  drug resistant strains, due to patients not
  completing antibiotic courses.
• In 1980 50 per cent of TB bacilli were resistant
  to 1 drug.
• Multi-drug resistant TB (MDR-TB) began to emerge.
  There are now an estimated 1.5m MDR cases
  worldwide.
• Extreme drug resistance (XDR-TB) was reported in
  2006.
• The first completely drug resistant (CDR-TB) case
  was reported in Italy in 2007.

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Yellow Fever

• Yellow fever was formerly a jungle disease, but
  it is now endemic in Latin American cities.
• Aedes aegypti is actually more common in North
  America, prompting fears that yellow fever could
  become endemic if there was a sufficient
  reservoir of infection.

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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 O1-El Tor strain). It spread to Latin
  America in the 1980s. Developed countries have so
  far escaped.
• An even more virulent strain (O139) 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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Endemic Cholera Areas ca. 2004
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Bubonic Plague

• A bubonic plague epidemic in India in 1994
  infected 2,500. Fortunately it had low virulence
  and was amenable to tetracycline.
• Bubonic plague is endemic in the US, but only in
  ground burrowing rodents. Introduced in 1900 in
  San Fransisco during the 3rd pandemic. Has been
  spreading east ever since.

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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 (e.g. MRSA) or poor (e.g. 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.