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.

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

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.

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.

A new strain of H5N9 bird flu was detected at a commercial duck operation in California's Merced County. All the ducks were euthanized.

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 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.

The U.S. is reporting its first confirmed outbreak of H5N9 avian flu at a California duck farm amid a global surge in its sister strain H5N1, according to a report from the Paris-based World Organization for Animal Health (WOAH).

Commercial duck flock in California has tested positive for two strains of avian influenza. On November 23, 2024, two HPAI viruses were identified in samples from a farm rearing meat ducks in Merced County in California. Increased mortality was observed at the premises, leading the state veterinary authority to quarantine the farm.

Avian influenza has led to a shortage of eggs and wholesale prices that are through the roof. Consumers can expect to feel the pain for a while.