Lecture 19 : New Infectious Diseases 1 Overview

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Lecture 19 New Infectious Diseases (1)Overview

• AIDS / HIV
• OTHER EXAMPLES
• Dengue Haemorrhagic Fever
• Kyasanur Forest Disease
• Machupo (Bolivian Haemorrhagic Fever)
• Marburg
• Lassa Fever
• Ebola
• Rift Valley Fever
• Sin Nombre

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AIDS / HIV

• Unusual prevalence of Karposis sarcoma and
  pneumonocystis carinii observed in USA in 1981.
• Syndrome became known as Acquired Immune
  Deficiency Syndrome.
• HIV virus identified by Luc Montagnier in 1984
  HIV-2 identified in 1985.
• HIV is a retrovirus which attacks the bodys
  immune system.

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AIDS / HIV (2)

• Transmission is via transfer of infected cells
  sexual (M-M, M-F) blood and blood products (e.g.
  factor VIII) infected needles (medical, ivdu)
  perinatally (foetal, breast milk).
• Not transmitted by casual contact, mosquitoes,
  kissing.
• There may be a long incubation period between
  initial infection and onset of full-blown AIDS.
• AIDS has killed 25 million people, and a further
  33 million are HIV positive (2007 figures).
  Annual infections still exceed deaths.
• AIDS has massive social and economic
  implications, especially for African countries.
• Compared with most diseases, AIDS is not very
  infectious.

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Dengue Haemorrhagic Fever

• Dengue (breakbone fever) is a long established
  disease in tropical countries caused by a virus
  transmitted by Aedes mosquitoes.
• In 1953 it mutated to a haemorrhagic form
  (Dengue-2) in the Philipines and SE Asia.
• 15 per cent case fatality rates.
• Asian tiger mosquito (Aedes albopictus) invaded
  the US in 1985. It out-competed local mosquitoes
  and is now widespread over southern US states.
• Can also carry yellow fever and 6 types of
  encephalitis.

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Aedes Aegypti (blue) Dengue (red), 2006
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Kyasanur Forest Fever

• After independence people began clearing forests
  to create grazing for cattle.
• Disease observed in monkeys in 1955.
• Humans began dying from a haemorrhagic fever in
  1957.
• Case fatality rate was 20 per cent.
• Caused by virus transmitted by ticks from cattle,
  but commensal source of the virus has never been
  identified.
• Monkeys were also victims.

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Machupo (Bolivian H. Fever)

• Cattle farms owned by Brazilians were
  expropriated in 1952 revolution.
• Peasant proprietors cleared jungle to grow corn,
  disrupting the habitat of a fieldmouse (Calomys
  callosis).
• Mice population thrived on corn husks. As numbers
  increased they moved into towns, where cat
  population had been decimated by DDT spraying
  against malaria.
• Mice carried a virus which was passed in their
  urine, contaminating food sources.
• Epidemic affect 40 per cent of the population
  case fatality was 50 per cent.

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Other S.American H. Fevers

• Other South American haemorrhagic fevers include
• Junin (Argentinian haemorrhagic fever, 1953).
  Virus transmitted by fieldmouse Calomys
  musculinus which multiplied following expansion
  of grain growing in the pampas.
• Oropouche (1961). First outbreak was in Brazil.
  Transmitted by midges that breed in pools of
  water created by cacao husks. Epidemics have
  spread to other countries.
• Guaranito (Venezuelan haemorrhagic fever, 1989).
  Transmitted by rodents.

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Marburg

• Observed in monkeys in 1961.
• Jumped species from monkeys inported into Germany
  by a pharmaceutical company in 1967.
• Source of virus has never been identified.
• Angola epidemic in 2004-5 had gt90 case fatality.

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Lassa Fever

• Identified in Nigeria in 1969, but it may have
  been around longer but was possibly confused with
  malaria or yellow fever.
• Now endemic in large parts of west Africa.
• 10 per cent case fatality.
• Reservoir has been identified as a brown rat
  (Mastomys natalensis) which replaced black rat
  killed off by humans.

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Mastomys natalensis
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Ebola

• First outbreaks were in southern Sudan and
  north-east Zaire (Democratic Republic of the
  Congo) in 1978.
• Caused by different strains.
• Highly infectious and highly lethal (90 per cent
  case fatality).
• Pygmies in Cameroon and Central African Republic
  carry antibodies, but no evidence of disease.
• Source still unknown.
• Monkeys in Philipines carry a third strain.
  (Sudan strain is closer to Philipines strain than
  it is to Congo strain).

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Ebola
Lassa Fever
Marburg
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Rift Valley Fever

• Established disease of sheep and cattle in
  Africa, but epidemic affected 200,000 people in
  Egypt (600 deaths) in 1977.
• Transmitted by mosquitoes.
• Mosquito population is thought to have multiplied
  due to changes in the water table following the
  building of the Aswan dam (1971).
• Similar outbreak in Mauritania in west Africa
  after the Senegal river was dammed.

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Sin Nombre

• Navajo indians in the four corners in the US
  hit by strange illness in 1993 75 per cent case
  fatality.
• Caused by a virus carried by Peromyscus
  maniculatus (deer mouse).
• Abundant supply of penon nuts after two mild
  winters caused mouse population to expand
  tenfold.
• Virus passed in urine is thrown up in dust during
  cleaning.
• Navajo tell of whole families being wiped out
  after spring cleaning as far back as 1919.

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Summary

• There are many other new diseases not mentioned
  e.g. Legionnaires disease (1976) Lyme disease
  (1977) SARS (2003).
• There are also old rare diseases which are
  becoming more common (e.g. Creuztfeldt-Jakob), or
  appearing in new locations (e.g. West Nile in New
  York, 1999).
• So far the more serious threats have remained in
  the tropics, but there have been a few near
  misses (e.g. Ebola in Reston VA, 1989 and
  Johannesburg, 1996).