Avian influenza A(H5N1) in humans and in poultry in Asia: food safety considerations
24 January 2004 -- The recent outbreaks of highly pathogenic H5N1 avian influenza in poultry in Viet Nam and similar reports from several countries in the region have sparked concern about the source of infection and the risk of human transmission. The presence of avian influenza virus H5N1 in patients in Viet Nam and in Thailand have prompted renewed attention about the source of infection and spread of disease to humans.
Avian influenza is an infectious disease of birds. Migratory waterfowl - most notably wild ducks - are the natural reservoir of avian influenza viruses, and these birds are also the most resistant to infection. Domestic poultry, including chickens and turkeys, are particularly susceptible to epidemics of rapidly fatal influenza. Avian influenza viruses rarely affect humans and do not normally infect species other than birds and pigs. Its ability to cause severe disease in humans has now been documented on two occasions (Hong Kong SAR, 1997 and The Netherlands, 2003). Investigation of these outbreaks determined that close contact with live infected poultry was the source of human infection. Therefore, the practice of marketing of live poultry directly to consumers should be discouraged in areas currently experiencing influenza outbreaks among poultry.
WHO is aware of recent concern over the possibility that the avian influenza in addition to direct contact with live infected animals could spread through contact with contaminated poultry products. WHO is therefore working to determine if there is any evidence to suggest that avian influenza could be spread through contaminated foods. To date there is no epidemiological information to suggest that the disease can be transmitted through contaminated food or that products shipped from affected areas have been the source of infection in humans.
WHO has reviewed studies and reports received regarding the transmission of the disease. In the present outbreaks, in addition to chickens, reports indicate that pigs and ducks have also been infected. Infected chicken flocks would rapidly develop symptoms and should be destroyed before having any possibility of entering the food-chain. Ducks have been reported to be asymptomatic carriers and duck products could be contaminated with the virus. In one recent study, a highly pathogenic strain of avian influenza H5N1 has been isolated from imported frozen duck meat. The public health significance of such findings is not well understood but believed to be very limited since further processing would inactivate the virus. In general, good hygiene practices during handling of raw poultry meat and usual recommended cooking practices for poultry products would lower any potential risk to insignificant levels. Eggs from infected poultry could also be contaminated with the virus and therefore care should be taken in handling shell eggs or raw egg products.
Some knowledge is available about the effect of food handling and treatment on the influenza virus. While freezing and refrigeration would not substantially reduce the concentration or virulence of viruses on contaminated meat, proper cooking kills such viruses. In general, WHO recommends that foods should be cooked to reach an internal temperature of 70°C.
While trade restriction have been put in place by some countries to protect animal health, on the basis of presently available data, WHO does not at present conclude that any processed poultry products (whole refrigerated or frozen carcasses and products derived from these) and eggs in or arriving from areas currently experiencing outbreaks of avian influenza H5N1 in poultry pose a risk to public health. WHO continuously emphasizes the importance of good hygiene practices during handling including hand washing, prevention of cross-contamination and thorough cooking of poultry products. WHO will continue to closely monitor the evolution of the current outbreaks, in collaboration with Ministries of Health and our partner agencies.