Indirect transmission can spread bird flu

ATHENS, Ga., June 8 (UPI) -- U.S. scientists have created the first model of the avian influenza viruses that takes into account both direct and indirect transmission among birds.

University of Georgia researchers said their model has the potential to shed new light on how outbreaks begin in wild bird populations.

"The environmental transmission of avian influenza among birds is quite rare, but our model shows that it can play an important role in outbreaks," Professor Pejman Rohani, the study's lead author, said. "There are situations where ignoring the possibility of environmental transmission would cause you to significantly underestimate the probability, magnitude and duration of an outbreak."

Rohani said current models of avian influenza only take into account the direct transmission of the virus that occurs when infected waterfowl and shorebirds shed the virus in their feces and those nearby drink contaminated water. But the new study shows some avian influenza viruses can persist in water for up to 150 days.

So even when no infected birds are present, Rohani said, virus present in the water can trigger an outbreak. He said models that only take into account direct transmission would incorrectly conclude there is no risk of an outbreak when no infected birds are present.

The findings appear in the early online edition of the Proceedings of the National Academy of Sciences.