Natural wild bird flus are mild; it's evolutionary

letter I've just had published in the Independent (UK):

Don't blame deadly flu on wild birds

Sir: I am an ornithologist based in Hong Kong, and since 2003 have followed the spread of H5N1 and the purported role of wild birds. I was surprised to read Sir Hugh Pennington's assertion (letter, 19 March) that "the evidence that these viruses [highly pathogenic avian influenzas] evolve in wild birds and are spread by them is overwhelmingly strong," as this contradicts all evidence I am aware of.

Natural wild bird flus are mild. However, in poultry farms these influenzas can evolve to higher virulence: as the Food and Agriculture Organisation notes, "Outbreaks of HPAI originating from low pathogenic viruses carried from wild birds have occurred relatively frequently in domestic poultry in the last decade."

An FAO table lists 28 highly pathogenic avian influenza outbreaks from 1959 to 2004. All were first recorded in poultry. There are sound evolutionary reasons for wild bird flus being mild. As noted by the evolutionary biologist Paul Ewald, flu must be directly transmitted from carriers.

With wild birds, it is useless to the virus if birds become very sick or die. But in poultry farms, even very sick or dying birds can transmit virus, leading to virulent forms evolving. These evolutionary principles continue to apply with H5N1.

No bird species has been shown to survive and sustain and spread this virus; instead, the vast majority of wild birds confirmed to have been infected with H5N1 were dead. Here in east Asia - the epicentre of H5N1 - there has been no report of H5N1 in a migratory wild bird since last summer.

DR MARTIN WILLIAMS HONG KONG

O

in response to this:

Blame wild birds

Sir: Caroline Lucas has a point ("Wild birds are not to blame for spreading avian flu", Opinion, 18 April).

The first scientifically studied outbreak of highly pathogenic bird flu started in Italy in 1901 and was spread to Austria by bird fanciers exhibiting at a show. The return home of the fanciers after its panic closure helped even more. But to say that intensively farmed flocks are the explosive charge is rhetoric, not science.

The evidence that these viruses evolve in wild birds and are spread by them is overwhelmingly strong. They were killing birds long before the giants of the global industry were heard of.

HUGH PENNINGTON PRESIDENT, SOCIETY FOR GENERAL MICROBIOLOGY, READING

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Futher evidence/proof re wild bird flus being mild:

Tests on nearly 75,000 wild ducks, gulls and other birds have turned up no sign of dangerous H5N1 avian influenza in the United States, a federal agency said on Thursday.

"The program was unprecedented in scope in terms of the range of species of birds sampled, which included waterfowl, shorebirds, gulls and terns, among others," Hon Ip of the U.S. Geological Survey said in an e-mail posted to an infectious-disease message group. "As of today, the testing of over 74,506 samples in wild birds from across the United States has been completed, and no highly pathogenic avian influenza viruses have been found," said Ip, who works at the USGS National Wildlife Health Center in Madison, Wisconsin ... The tests did turn up several samples of a low-pathogenic H5N1 virus, which is not particularly dangerous to either birds or to people, the USGS reports on its Web site

Canada has run similar surveys and found no dangerous bird flu. Birds infected with low-pathogenic H5N1 were found in states including Delaware, Illinois, Michigan, Pennsylvania and Maryland. This virus is apparently not dangerous to the birds, although Ip said he wanted to study infected birds to see if it has subtler effects on their ability to survive and migrate.

U.S. wild-bird survey finds no evidence of H5N1