Transmission electron micrograph of
Avian Influenza Virus.
(click image for larger view in its own window)
I just received a message from ProMED-email regarding the appearance of the avian influenza virus that was just identified in Nigeria. ProMED-email is a program of the International Society for Infectious Diseases that serves to keep medical personnel and other professionals up-to-date on emerging diseases around the world. In this message, Debora MacKenzie, a writer for NewScientist.com news service, points out that;
The article [in NewScientist.com] was posted before we found out the strain in Nigeria is apparently Qinghai, that is, the same one found in wild birds at Qinghai Lake, then across Siberia, then in Turkey and around the Black Sea coast. That is exactly what one expects for wild bird spread. (The probability of that spread was also strongly supported by a PNAS [Proceedings of the National Academy of Sciences] paper this week, Chen et al.) This might theoretically be down to people shipping infected meat or poultry waste to the affected areas, but I can’t see why that would all be exactly the same strain of H5N1 every time, and never the Z genotype that has dominated east Asian outbreaks.
Despite the evidence that wild birds are now carrying H5N1 across long distances during migration, the data still do not show that wild birds are a significant source of the virus in local areas, nor do wild birds spread the virus to humans. Instead, domestic poultry serve as the primary source, as Debora notes;
That PNAS paper also showed it is poultry that maintain the virus in a region, spread it locally, and give it to people, not wild birds. [italics mine]
You are probably aware that for years, I have strongly asserted that there has been no evidence that wild birds been the source of avian influenza and, until recently (2005), there has been no evidence that wild birds have been spreading this virus, particularly since there were and are so many other routes of spread available; the domestic poultry industry and cock fighting birds, in particular. Knowing the details of viral spread is important because it affects public health policies, for example;
Now the virus is in poultry in Africa; that is where action must be taken: stamping out, and if possible, giving African farmers the means to isolate their poultry from wild birds, a tall order. But any action taken against wild birds in Africa now, as the FAO and bird experts have repeatedly said, is a very bad idea; it will not solve problems caused primarily by poultry and will just make matters worse by dispersing the birds.
Further, thanks to the “magic” of evolution, H5N1 will become less lethal as time goes on, unless it is maintained by humans in their flocks of domestic poultry; birds that are typically kept under closely-packed and unhygienic conditions;
Virologists say the H5N1 virus will evolve into insignificance in wild populations as long as it is not replenished by continued maintenance of the highly pathogenic strain in the poultry, where it probably evolved [italics mine].