The H5N1 avian flu virus infected three dairy herds in California’s Central Valley, the first time the disease has been confirmed in the nation’s largest milk-producing state, said officials. California was the first new state to be hit by the disease since Oklahoma reported cases on July 11.
Counting California, bird flu has been discovered in 197 herds in 14 states from coast to coast. The California state veterinarian ordered a quarantine of the infected farms. “Animal movement is being tracked and evaluated, as are other potential [disease] introduction pathways,” said the state Food and Agriculture Department. The USDA says the virus moves from cow to cow and from herd to herd, sometimes through shared equipment and contaminated clothing.
The risk to the general public is low, says the Centers for Disease Control. Thirteen livestock workers have contracted mild cases of bird flu from contact with infected chickens and milk cows since April 1; 10 of the cases were in Colorado.
“We have been preparing for this possibility since earlier this year when HPAI [highly pathogenic avian influenza] detections were confirmed at dairy farms in other states,” said Karen Ross, California Food and Agriculture secretary. “Our extensive experience with HPAI in poultry has given us ample preparation and expertise to address this incident, with workers’ health and public health as our top priorities.”
The USDA follows a strategy of isolating infected farms and waiting for the virus to die out among infected herds. It requires farmers to test lactating dairy cows for the H5N1 virus before shipping cattle across state lines. Milk from infected cows has a high H5N1 viral count.
Federal public health and animal health officials have faced questions about whether their they are doing enough to stop the spread of the virus among dairy cattle as well as the risk the virus could adapt further to become communicable among people. The CDC says that 230 people have been tested for the H5N1 infections since late March following exposure to infected animals.
Scientists say bird flu among dairy cows was the result of a single disease spillover in the Texas panhandle in late 2023 or early this year. Interstate sales of dairy cattle are common.
There were 1,117 dairy farms with 1.69 million milk cows in California, according to the 2022 Census of Agriculture. California produces 18 percent of the milk in the country. Wisconsin is second with 14 percent.
Nearly 101 million birds in domestic flocks have died of HPAI since it first appeared in the United States in February 2022. The disease has been found in wild and migratory birds in every state.