December 8, 2008

Study reveals bird flu makes mallard ducks thin

New research from Sweden reveals that bird flu can make mallard ducks thinner than other ducks.

In a study conducted by Jonas Waldenstrom of Sweden's Kalmar University, Albert Osterhaus of Erasmus Medical Centre in Rotterdam and colleagues reported in the Proceedings of the Royal Society B: Biological Sciences said mallard ducks are a main reservoir--or a host of virus without becoming ill but capable of spreading it--for low pathogenic bird flu virus. Surprisingly, these birds do not physically manifest the viral infection, they said.

The team analysed 10,000 samples of migratory mallards in Sweden for bird flu virus and discovered that infected birds were leaner than uninfected birds, and that weight loss was related to the amount of virus shed in their faeces.

Although many mallard populations are migratory, the short virus shedding times (often less than a week) imply that individual birds are not long-distance dispersers of the virus on a continental scale, they said.

The scientists however did not find how far the birds have migrated. On average, the ducks were infected eight days and spread the virus for just three of them in their droppings.

The study concluded that the "short virus shedding time suggests that individual mallards are less likely to spread the virus at continental or intercontinental scales."

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