Transcript Document

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Ginny Codd
Viruses: Infection
and Ecology
Zoonotic Disease
Rapidly emerging viral infections
• Zoonosis: Transmission to human from non-human vertebrate
• Examples in USA:
– Monkey pox – chimpanzee (importation as pets)
– Lyme disease – deer, deer mice ticks (urban expansion + proximity to
deer population)
– Hanta virus - mice
(recall Helen’s Four corners trailer tale)
– SARS – corona virus – quail – human
– H5N1 – oxym virus – poultry – human
"Habitat" of influenza A viruses. Ecological and phylogenetic studies suggest that wild waterfowl are
the principal reservoirs for influenza A viruses, which occasionally are transmitted to other host
animals such as horses, pigs, and chickens, leading to influenza outbreaks among these species. Some
of the viruses may become established in these new hosts and cause epidemics and epizootics.
Viruses are transmitted among these new host animals (e.g., between humans and pigs or between
chickens and humans, as occurred in 1997 in Hong Kong).
Potential for virulence and genetic mutation:
Determinants affecting pathogenicity of influenza virus
-HA cleavability
-PB2 amino acid at position 627 and others
-NS1 protein
– SARS(corona virus) and H5N1–both RNA viruses show ease
of variation in:
mutation + deletion + reassortment + recombination.
– Clusters isolated in Indochina ( Cambodia, Laos, Malaysia,
Thailand and Vietnam genetically and antigenetically similar
– Clusters isolated in China, Indonesia, Japan and Sth Korea
show greater genetic divergence.
– Rapid mutation of the virus in Vietnam.
H5N1Public Health Threat
• Globalization:
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Challenge in isolation of outbreaks
Threat to global markets – international commerce
International trade – livestock, birds
$6 billion global Illegal trade – exotic animal and plant species
• Population Density:
– Increased expansion and concentration:
– increased risk of zoonotic transmission
– greater proximity of human and non-human vertebrates.
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Agricultural methods
Deforestation
• ‘Weaponized’ virus:
– Pathogens as biological weapon
– Deliberate or accidental release of genetically modified highly virulent
strains
Asian Wet Markets
• Wet markets:
Selling of live animals, vertebrate and invertebrate at market
– SARS ( corona virus)
– Live Himalayan palm civet in southern China
– H5N1
– Live quail
Changes in practices
Hong Kong – aquatic birds eliminated/sold chilled
quail eliminated
introduction of two ‘clean days’ per month
inactivated vaccine on poultry markets
improved sanitation
Indochina peninsula – greater challenge in implementing change
geographical diversity
Geographical Distribution ( Feb 2004)
Vaccination
Chicken
Human
600,000 doses to chicken in Ho Chi
Minh city ( april 2005)
Current practice in Hong Kong and parts
of Mainland China that serve the HK
market.
Current methods
Egg-based manufacture ( 300+ million
eggs needed annually for influenza)
6-9 months to develop
Dedendant upon effective method for
production and equitable
distribution
Potential emerging practice:
Genetic engineering of strains containing the correct prescription of genes
Reverse recombination
Anti-virals
• Amantadine
• Rimantadine
• Neuraminidase inhibitors
-Tamiflu (oseltamivir)
Zanamivir
So what if ?………
• Pandemic of immense proportion
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1968 pandemic: China population 790 million
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2004
Pig population 5.2 million
Poultry population 12.3.million
China population 1.3 billion
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Pig population 508 million
Poultry population 13 billion
If H5N1 were to mimic 98 pandemic predict 1.7 million deaths U.S.
180 – 360 million deaths globally
• Halt to global economy
• Lack of medical resources
• Inadequacy of vaccines and anti-virals
– Production and availability.
What are we doing about it?
• World health organization ( WHO)
- meeting in Manila in May to address global
concerns.
- focus on increased surveillance
- vaccine development
- education and change of farming and market
practices