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Lecture 8: New Infectious Diseases Overview

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Title: Lecture 8: New Infectious Diseases Overview


1
Lecture 8 New Infectious DiseasesOverview
  • AIDS / HIV
  • NEW INFECTIOUS DISEASES - FACTORS
  • EXAMPLES
  • Machupo
  • Marburg
  • Lassa Fever
  • Ebola
  • Rift Valley Fever
  • Sin Nombre
  • Other
  • CONCLUSION

2
AIDS /HIV
  • The discovery of AIDS / HIV in the early 1980s
    shattered the illusion than major infectious
    diseases were a thing of the past in developed
    countries.
  • HIV attacks the immune system. HIV is capable of
    splicing DNA into the DNA of the host cells, so
    instead of controlling HIV the immune system
    helps reproduce it.
  • About 40m people have been infected by HIV
    worldwide. The worst affected region is
    sub-Saharan Africa where it is transmitted
    heterosexually.
  • Infection in developed countries is still mainly
    amongst homosexual men and intravenous drug users.

3
New Infectious Diseases
  • AIDS / HIV is by no means the only new infectious
    disease. There have been about 30 new diseases
    discovered in the past 20 years.
  • Most originate in tropical countries, and most
    have so far been confined to these regions.
  • The fear in developed countries is that one of
    these new diseases may be transmitted to a
    susceptible population in the developed world.

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5
Factors
  • New infectious diseases may be regarded as a
    by-product of the knock-on effects of population
    growth.
  • The increased demand for food has resulted in new
    areas being brought under cultivation, disrupting
    existing ecosystems
  • Monocultivation has reduced biodiversity, forcing
    viruses to seek new hosts
  • Rapid urbanisation results in high population
    densities and insanitary conditions
  • Global warming is extending the habitats of
    mosquitoes and other vectors
  • Competition for resources contributes to wars
    which disrupt public health systems and trigger
    mass population movements.

6
Examples - Machupo
  • Machupo (Bolivian Haemorrhagic Fever) originated
    in 1961 in the headwaters of the Amazon where the
    traditional cattle ranching / export economy was
    replaced by self-reliant peasant agriculture
    after a social revolution.
  • Jungle was cleared to grow corn and vegetables,
    disrupting the habitat of Colomys callosis (a
    field mouse).
  • The mouse population swelled given the
    availability of corn. They invaded the villages.
  • A virus carried by the mice was passed by the
    mice in their urine.
  • The virus in humans caused 50 people mortality.
  • The disease was eventually contained by catching
    the mice.

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Examples - Marburg
  • The Marburg virus causes a horrific disease.
  • It was first observed amongst monkeys in 1961,
    but humans were infected in 1967 by monkeys
    imported into Germany from Uganda to be used to
    produce vaccines.
  • The reservoir (i.e. the source which infected the
    monkeys) has never been discovered.

9
Examples Lassa Fever
  • Identified in Nigeria in 1969, but it is believed
    to have been around for a few decades before (but
    confused with malaria or yellow fever).
  • It resembles malaria in the early stages, but
    this is followed by haemorrhaging.
  • Now endemic in parts of west Africa.
  • The reservoir has been identified as Mastomys
    natalensis (a brown rat) which thrives because
    humans killed off the larger black rat.
  • It is fatal in about 10 per cent of cases.

10
Examples - Ebola
  • Occurred almost simultaneously in two locations a
    few hundred miles apart in Zaire (Congo) and
    Sudan.
  • Ebola is a horrific disease with 90 per cent
    mortality.
  • Transmission is by direct contact, but it is very
    contagious.
  • The reservoir of the virus has never been
    discovered.
  • Infected monkeys from the Phillipines almost
    caused an outbreak in Reston VA, near Washington
    in 1989.

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Examples Rift Valley Fever
  • Originally confined to sheep and cattle in
    Africa, it jumped species and affected 200,000
    people in Egypt in 1977.
  • The virus is transmitted by a mosquito.
  • The 1977 outbreak is believed to have been
    triggered by the construction of the Aswan dam
    which created favourable conditions for the
    mosquitoes to breed.
  • There was a similar outbreak in Mauritania after
    the Senegal river was dammed.

13
Examples Sin Nombre
  • Indians on the Navajo reservation in the south
    west USA were afflicted by a strange illness
    causing 75 per cent mortality.
  • Caused by a virus carried by Peromyscus
    maniculatus (deer mouse).
  • Two moist winters (caused by El Nino) resulted in
    an abundant crop of Penon nuts and a 10-fold
    increase in the mouse population.
  • The mice invaded homes and transmitted the virus
    in their urine.

14
Examples Lyme Disease
  • Unknown before 1962, but now the most common
    vector disease in the USA.
  • Caused by a bacteria transmitted by bites from a
    tick that lives on deer.
  • Lyme disease has increased due to former farm
    land reverting back to scrub which favours the
    growth of the deer population.
  • Especially common in the suburbs where people
    come in contact with the deer population.

15
Examples Other
  • Dengue Haemorrhagic Fever. Originally confined to
    South East Asia, but now a growing threat in
    other areas including the southern USA due to the
    diffusion of the vectors (Aedes aegypti or Aedes
    albopictus).
  • Latin American Haemorrhagic Fevers (Sabia,
    Guaranito, Junin). Similar causes to Junin i.e.
    expansion of agriculture into new areas.

16
Conclusion
  • Developed countries may be protected from the new
    vector borne diseases because the vectors may not
    be present in developed countries.
  • Diseases transmitted by person to person contact
    can hopefully be controlled.
  • The main risk to developed countries is the
    possibility of a new air-borne disease. Hence the
    concerns about SARS (2003) and Asian bird flu
    (2004), both of which originated in Asia.
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