Monday, April 24, 2006

Et tu, pigeons?

Don't worry about pigeons and bird flu, we're told. Well I wasn't, since there is so much else to worry about, but now that they've brought it up, let's take a look.

In an AP story that is all over the bird flu news today, we find the following:
City folks, don't worry. Nobody expects pigeons, more common than manhole covers, will bring the deadly bird flu virus.

Pigeons are not immune from the virus. But tests indicate the birds pick it up only when they are exposed to very high doses, do not always become infected under those conditions and are carriers only briefly.

"Pigeons aren't a big worry," said Rex Sohn, a wildlife disease specialist at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wis. "But to make absolute predictions that pigeons won't be susceptible to this virus, in whatever form it arises in North America, is not something you want to say." (AP)
I guess you don't want to say them because we know some pigeons are susceptible to the virus, as the very same story lays out in detail. The Agriculture Department's Southeast Poultry Research Laboratory in Athens, Ga. has been studying it since 1997 or so and the results were said to have produced more questions than answers. Hmmm.

Using the virus that surfaced in Hong Kong (the story doesn't say from a bird or a human), USDA researchers couldn't infect pigeons, even with direct instillation into their mouths with doses orders of magnitude higher than would be encountered in the wild (they say; I'm not sure what this is based on). But in 2004, using high doses of isolates from a pigeon and a crow in Thailand, seven out of 12 pigeons were infected, with one death. This year, a 14 year old Iraqi pigeon seller contracted bird flu and died. So pigeons can be infected, although at this point they are not as susceptible as chickens or ducks, and while they carry the virus for more than a week, they are said not to be infective for more than a day or two. Maybe. The virus is changing and finding new hosts. Why not pigeons?

We can agree with the bottom line, summed up in the AP story:
"The experimental data is not very strong that pigeons are going to be spreading this virus around," [Southeast Poultry Research Laboratory Director David] Swayne said. "At this point they have not been implicated in spreading it to humans and to farms."
So it's true that pigeons aren't a big worry now. "At this point."