Do migratory birds spread bird flu viruses? It seems to be the case. Wild waterfowl are considered the natural reservoir of all influenza A viruses. They have probably carried influenza viruses, with no apparent harm, for centuries. They are known to carry viruses of the H5 and H7 subtypes, but usually in a mild form. Considerable circumstantial evidence suggests that migratory birds can introduce mild H5 and H7 viruses to poultry flocks, which then mutate to the highly virulent form. The H5N1 virus is also of particular concern for human health.
In the past, dangerous viruses have been isolated from migratory birds on very rare occasions involving a few birds, usually found dead within the flight range of a poultry outbreak. Recent events make it likely that some migratory birds are now directly spreading the H5N1 virus in its highly dangerous form. Further spread to new areas is expected.
What is are the current outbreaks in poultry concerning?
The current outbreaks of highly pathogenic avian influenza, which began in South-east Asia in mid-2003, are the largest and most severe on record. Never before in the history of this disease have so many countries been simultaneously affected, resulting in the loss of so many birds.
The causative agent, the H5N1 virus, has proved to be especially hardy. Despite the death or destruction of an estimated 150 million birds, the virus is now considered endemic in many parts of Indonesia and Viet Nam and in some parts of Cambodia, China, Thailand, and possibly also the Lao People’s Democratic Republic. Control of the disease in poultry can take several years. Hopefully, the outcome will be fine. But, meanwhile, all must be done to ensure human safety.