Three dairies in central California have tested positive for avian flu, the first time the virus has been discovered in the state after spreading across the United States since March. (Image by Charlie Boyd from Pixabay)

Aug. 31 (UPI) -- Three dairies in central California have tested positive for avian flu, the first time the virus has been discovered in the state after spreading across the United States since March.

On Friday, the California Department of Food and Agriculture confirmed the cases of the highly pathogenic avian influenza, or H5N1. The virus is fatal to poultry and makes cows mildly sick with symptoms of lethargy, loss of appetite and dehydration.

No human cases of HPAI have been confirmed in California related to this incident.

The risk to humans is considered low, according to California Department of Public Health and the Centers for Disease Control and Prevention. The total reported human cases are 14 since 2022, with four after exposure to dairy cows, according to the CDC. Nine of the H5 human cases have been confirmed as H5N1.

The primary concern is for dairy workers in close contact with infected dairy cows.

Herds in California began showing clinical signs consistent with HPAI on Sunday.

Samples were submitted to the California Animal Health and Food Safety, and then to the National Veterinary Services Laboratory.

California State Veterinarian Dr. Annette Jones did not identify the county but said the dairies are located in "an area of the Central Valley where dairies are concentrated."

The top three milk producers in the state are Tulare, Merced and Stanislaus counties. The state will also begin testing cows in nearby dairies and any poultry ranches for the avian flu, Jones said.

Jones said the affected dairies will be placed under quarantine, requiring enhanced bio-security measures, including wearing protective equipment and disinfecting equipment.

She said the healthy cows on the affected dairies have been cleared to continue shipping milk to processors for pasteurization to kill the virus and other harmful bacteria.

"This is a tough time for our dairy farmers given the economic challenges they're facing in a dynamic market, so I want to assure them that we are approaching this incident with the utmost urgency," CDFA Secretary Karen Ross said in a news release.

The virus was first reported in U.S. dairy cows on March 25 in Texas, most likely due to a single spillover event from wild birds. Since then it has been found in 13 states and has infected 192 herds.

Despite the low risk to humans, nearly 5 million doses of flu vaccine are being prepared for possible use in humans.

The avian virus has been detected in wild birds in the U.S. since 2022.

A study released in March found the bird flu is now jumping between species of mammals, a step that draws the virus closer to hopping into human beings.

Researchers have tracked transmission of avian influenza between dairy cows in herds, as well as from cows to cats and a raccoon.

Genetic analysis of the virus did not reveal any mutations that would lead to enhanced transmissibility of H5N1 in humans, said senior researcher Dr. Diego Diel, director of the Virology Laboratory at the Animal Health Diagnostic Center in the Cornell University College of Veterinary Medicine.

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