Bird flu infections around the U.S. have forced mass cullings and resulted in the deaths of zoo animals and pets

First U.S. detection of virulent H5N9 strain, at a California duck farm, draws scrutiny as evidence of genetic reassortment that could trigger human outbreaks.

The government is investigating a rare strain of avian flu, H5N9, detected on a duck farm in central California, according to the World Organisation for Animal Health. It marks the first reported outbreak of this strain in U.