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.

According to the Centers for Disease Control and Prevention, bird flu outbreaks have impacted poultry in 51 states, while the virus has been detected in dairy cows across 16 states.

Animals at 25 egg and dairy production facilities, including one backyard coop, have tested positive, says the county health department.

Both H5N9 and H5N1 were detected at the duck farm in Merced County, according to tests conducted by the US Department of Agriculture (USDA) National Veterinary Services Laboratory. The event began on November 23, with clinical signs that included increased deaths in the ducks.

The H5N9 strain of avian influenza is much more rare than the H5N1 which has been responsible for most of the reported human cases and the first human death.

Bird flu is now believed to be widespread in Massachusetts and is likely present even in places where there has not been a confirmed positive, state environmental and health officials said Wednesday.

Rose Acre Farms, the nation's second largest egg producer, said yesterday that tests have confirmed avian flu at its facility in Seymour, Indiana, which could further stretch the supply of eggs as commercial farms in several states continue to battle the spread of the H5N1 virus.

Minnesota and Iowa were added to the National Milk Testing Strategy on Jan. 8. There are now 36 states involved in the testing for the avian influenza virus.

Bird flu, or Avian influenza, is a virus that is spread from infected cows, birds and other animals to people.

The nationwide spread of highly pathogenetic avian influenza, HPAI, also known as avian or bird flu has many in Illinois concerned about livestock,

In Riverside County, 23 dairy and poultry farms including one backyard flock have tested positive for Avian influenza (bird flu), a virus spreading through wild birds around the world causing outbreaks in poultry and dairy cows.