Wild birds to blame for avian flu outbreak? Not so fast, say scientists

Wildlife disease experts are calling into question reports suggesting that wild birds may be to blame for the recent worldwide outbreak of the highly pathogenic avian flu, H5N2. The virus has spread from Asia to Canada to, most recently, the Midwest. The USDA has suggested that recent cases are nearly identical to the Washington pintail duck virus--evidence, says the agency, that wild birds may be spreading the disease.

David Stallknecht

Now, scientists from the University of Georgia's College of Veterinary Medicine and the Minnesota Department of Natural Resources are questioning the USDA's hasty conclusion. Georgia's David Stallknecht called the notion that avian flu originated in wild birds "pure speculation" in a story posted by the University of Minnesota's Center for Infectious Disease Research and Policy (CIDRAP). "It is based on circumstantial evidence that is rapidly becoming accepted dogma," he said.

The avian flu saga dates back to late last year, when H5N2 struck several farms in British Columbia. That sparked surveillance programs in the U.S., which turned up cases of pintail duck virus in Washington and a related strain in a captive gyrfalcon nearby. Since then, cases of H5N2 have shown up in poultry in several states, including Idaho, Minnesota and Arkansas.

Still, says Stallknecht, no direct link between the wild strains and those found on poultry farms has been established. Michelle Carstensen, wildlife health program supervisor in the Minnesota Department of Natural Resources, agrees, adding that migratory patterns suggest it would be highly unlikely that wild birds are spreading the flu. That's because migratory birds fly from south to north at this time of year, she said, suggesting there could be different causes for the outbreaks in Minnesota and more southern states, she said.

Carstensen and her team have been testing fecal samples from wild birds found near the site of the outbreak in western Minnesota, and so far, only two ducks have tested positive for avian flu. The USDA is currently testing the samples to determine which strain of avian flu they were carrying.

So if wild birds aren't to blame for spreading avian flu, what is? Stallknecht suggests that people might actually be the problem. For example, travelers from Asia might have inadvertently carried the related H5N8 virus to North America and spread it to domestic backyard ducks. But he conceded in an interview with CIDRAP News that without proof, it's all just speculation.

The source of the virus has little impact on how authorities control it, Stallknecht added, but it could help prevent future biosecurity threats. "With regard to future risks for introductions of exotic viruses," he said, "it might be nice to know what really happened here."

- here's the CIDRAP News story

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