Tuesday, June 28, 2005

Bird die-off in China, etc.

Influenza virus's home in nature is in wild birds. Most of the viral subtypes are found only in birds, although a few have become adapted to other species like humans, pigs, horses and, of course, domestic fowl (poultry), which, while birds, are different than their wild counterparts in many ways. What happens in birds is both a warning and an influence on what happens in humans. So health experts pay attention.

What we have seen over the last two years is not only unprecedented but extremely worrying. Influenza A virus for the most part is of low pathogenicity in birds, so the emergence of highly pathogenic forms like H5N1 in recent years was an unpleasant surprise. Recently there have also been die-offs of wild migratory birds in species previously unaffected. H5N1 infection now is regionally widespread in asia and is poised to spread further. The recent reports of 1000 geese dying in western China (Qinghai province) has now been increased to 5000, according to the UN agencies WHO and FAO (Food and Agriculture Organization), who have a team in the area.
"This is the first time we've seen large numbers of migratory birds dying from bird flu," Julie Hall, the WHO official in charge of communicable diseases in China, said.

"So the virus has obviously changed to be more pathogenic to animals. What it means to humans we don't know." (Daily Telegraph, Australia)
There is some urgency to studying the birds on the large nature sanctuary on Qinghai's large salt-water lake, but of the almost 200 species of birds, only five have been tested so far. Because they will begin migration in a month or so, there is some urgency. The concern is that asymptomatic birds will carry the virus to distant places and a bird pandemic with H5N1 will spread to domestic poultry elsewhere. But another source of uncertainty and concern is that there is little information on where many of the bird species migrate (Bloomberg).

Meanwhile Vietnam has continued to see human cases in the absence of florid outbreaks in domestic poultry, unlike previously. Just what this means is unclear, but experts consider it a warning sign the virus has changed once again.

Although the usual "flu season" is over in Vietnam, there seems no respite from continued appearance of human cases. So far the numbers of officially counted sick people has been relatively small (unofficial count in Vietnam since December 2003 is 90, with 38 deaths). But no one is confident it will remain that way.