As an outbreak of the avian flu continues to wreak havoc on California agriculture, the number of infected animals and workers is stacking up.

As of Friday, state agriculture officials confirmed 294 dairies — representing a little more than 25% of the state’s 1,100 dairies — are now under quarantine due to the H5N1 avian flu.

On the state’s poultry ranches, more than 4 million turkeys and chickens have been killed in an attempt to stop the virus from spreading.

“It’s a mess,” said Bill Mattos, president of the California Poultry Federation. “Everyone is on high alert when it comes to bio-security measures.”

The virus is often fatal to poultry and spreads quickly among an infected flock. Without a cure, the only way to contain the virus is to depopulate all the affected and exposed chickens or turkeys.

Since 2022, the bird flu has been tracked in 48 states and has caused the destruction of 107 million birds.

Avian flu and California poultry

Hardest hit in California are poultry farmers in the San Joaquin Valley, home to two of the state’s largest poultry producers, Foster Farms in Livingston and Pitman Farms in Sanger.

Officials with both companies could not be reached for comment Friday, but industry spokesman Mattos said those who have been hit with the bird flue have suffered significant losses.

One of the largest depopulations recently took place in Kern County where 2.1 million egg layers were destroyed. On Thursday, state officials confirmed bird flu at a Fresno County turkey ranch with 17,500 birds and in Merced County with 53,200 turkeys.

Mattos said that poultry operators are using multiple bio security steps to prevent the virus from spreading, especially limiting who comes onto their farms, disinfecting common areas and wearing personal protective equipment.

One area that is much more difficult to control is preventing wild birds from congregating near poultry ranches. Migratory birds are common carriers of the bird flu and could be spreading the virus as they migrate from Canada to Central and South America.

“There are ducks everywhere these days,” Mattos said “We had an outbreak at a breeder ranch in Oakdale with nothing around the ranch. You can’t go in without showering or leave without showering. That is about as bio secure as you can get and there was still an outbreak.”

Infections at dairy farms

Dairy experts estimate the number of infections in the industry will likely grow until a majority of the state’s dairies are infected.

“There are many factors affecting the rate of this disease’s spread, foremost of which, certainly, is the high number of dairies in close proximity to one another,” said Dr. Michael Payne, a dairy researcher and instructor at the UC Davis School of Veterinary Medicine. “Additional challenges include the fact that an infected cow can shed (the) virus two weeks before she even exhibits symptoms. Add to that we have no effective vaccine for the disease, something which hopefully will change in the future.”

Payne added that California has dedicated a substantial amount of financial and personnel resources to identifying infected herds in real-time.

“We’re finding more affected herds simply because we are looking harder,” Payne said.

Unlike poultry, the avian flu is not typically lethal to dairy cows. If infected, the cow is separated from the rest of the herd as she recovers in about two weeks. Sick cows generally become lethargic and produce less milk.

Human cases of H5N1 avian flu

Also becoming a victim of the virus are dairy workers. The number of confirmed cases in California stands at 26 with the latest case being in Fresno County. Madera County health officials identified two cases on Nov. 14. One case was confirmed; the other is presumptive positive.

Symptoms in humans include cold and flu-like symptoms including conjunctivitis, cough, sore throat, runny or stuffy nose, diarrhea, vomiting, muscle or body aches.

The Fresno County Department of Public Health recommends all residents, especially workers at risk for exposure to bird flu, receive the seasonal flu and COVID-19 vaccine.

“Although the seasonal flu vaccine will not protect against bird flu, it can decrease the risk of being infected with both viruses at the same time and reduce the chance of severe illness from seasonal flu,” according to Fresno County health officials.

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