HPAI is not an infection transmitted to humans despite
the dire predictions and prognostications of doomsayers in the WHO and other
public health organizations with vested interests in acquiring funding and
resources. By Simon Shane
A recent epidemiological investigation conducted in
Cambodia clearly confirms that H5N1 strain HPAI responsible for the
panornitic in Asia is a disease of commercial and backyard poultry and by
accidental contact, free-living and migratory avian species. HPAI is not an
infection transmitted to humans despite the dire predictions and
prognostications of doomsayers in the WHO
and other
public health organizations with vested interests in acquiring funding and
resources.
Results of the comprehensive study are published in
Emerging Infectious Diseases. Participants included the Cambodian Ministry of
Health, Institute Pasteur,
WHO, Public
Health Department of Hong Kong and the US Centers for Disease Control
.
In March a poultry farmer in Kampot Province handled and processed chickens
presumably dying from HPAI. He subsequently became ill and died of H5N1
infection. An epidemiologic study was conducted among 93 households in close
proximity to the index case. None of the 351 residents showed antibody to H5N1
applying an indirect immunodiffusion test. The sample size and sensitivity of
the antibody detection procedure was capable of detecting at least one person
who had seroconverted, with a 95% probability, assuming a prevalence rate of 2%
in the population.
The conclusion from this study is that despite presumed
exposure documented in questionnaires the subjects were refractory to Avian Influenza. As noted in a commentary in May
, citing studies in the USA and Holland, the H5N1 virus
attaches to host cells in the respiratory mucosa using alpha 2-3 sialic acid
receptors. Humans, in contrast to avian species, carry alpha 2-6 sialic acid
receptors. The extensive contact between millions of village dwellers and
poultry farmers in SE Asia over the past seven years has yielded less than 250
confirmed cases, attesting to the relatively low susceptibility to infection.
Is concern over imminence of the "next influenza pandemic" in humans
justified given the apparent stability of the avian H5N1 virus? No. This is
based on current knowledge of the molecular biology of the three clades of the
virus that can be differentiated and the small number of human cases recorded,
despite opportunity for infection. Should public health authorities be concerned
over the HPAI panornitic? Certainly. From the human perspective, the threat of a
new influenza pandemic has focused on deficiencies in vaccine manufacture and
distribution, early detection of outbreaks, quarantine of populations and mass
treatment. These challenges are being addressed with varying degrees of efficacy
depending on available resources.
Does the ongoing H5N1 infection in avian species
represent a socio-economic problem? Certainly. The persistence of the disease in
poultry and wild birds suggests deficiencies in application of appropriate
control measures including detection and eradication, immunization of flocks,
imposition of biosecurity, education on hygiene and transition from live bird
marketing to consumption of processed poultry.
By: Simon
Shane
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