Avian influenza H5N1 is a disease of birds

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