The avian flu has made the jump to cattle, affecting livestock in at least nine states. While the virus has yet to appear in California cattle, experts in Marin County find the progression concerning.
The H5N1 virus, also known as HPAI or avian flu, usually only affects wild birds and poultry. However, in the beginning of April, the virus appeared in cattle and then in some people who worked closely with them. Experts in Marin County stress that it is mainly an occupational hazard, and the Centers for Disease Control and Prevention maintains that the public health risk is low.
“The main concern is the progression from a virus that really began as a bird flu that only affected birds to over the past couple years developing the ability to affect other animals, especially mammals,” said Dr. Matt Willis, the public health officer for Marin County. “That’s where we start seeing and raising the flag around a potential pandemic strain.”
Willis said the current danger appears to be minimal, and treatments for people are promising. In the two human cases reported, he said, symptoms were mild and antivirals used for more common flus were effective.
The virus transmissibility among humans seems limited, but Willis said it is not clear how livestock are being affected directly by the infected birds, or if it is spreading among cattle.
No H5N1 cases in cattle or livestock have been reported yet in Marin County or California, according to Scott Wise, assistant agricultural commissioner for the Marin County Department of Agriculture, Weights and Measures. The U.S. Department of Agriculture recently issued an order to restrict the movement of livestock across state lines, as well as require mandatory testing.
“That’s a concern, where it’s getting closer to home for us in Marin,” Willis said. “It could impact our livestock. It’s probably the most concerning shift, moving from birds to mammals.”
Wise said livestock that test positive for the flu are isolated from the herd and typically recover on their own, but the cow’s milk is thrown out. He said there is a significant concern among ranchers about the virus because it can take a while to move through the entire herd.
Wise said it helps that Marin County has closed herds, where ranchers keep self-sustaining populations of livestock in their own operations and do not introduce new animals from outside sources.
“Even though a single cow can recover within 10 days or so, the way the illness moves through a herd is like dominos,” Wise said. “It may take a significantly longer time for the overall disease to move through the entire herd, which leads to significant production loss with serious economic ramifications to the operation.”
Poultry farmers are already feeling the effects of the flu. While the mortality rate from the virus is about zero for cattle, it’s about 100% for poultry. In birds, the virus spreads fast and often the whole flock has to be euthanized to prevent the spread to other flocks.
In Marin County, more than 150,000 commercial poultry have died from the virus since the outbreak began in 2022, according to Wise.
“Economically, HPAI is devastating to both poultry and livestock producers and directly affects their businesses’ financial viability, and in turn the security of our food supply,” Wise said.
Wise said preventing H5N1 in animals is a two-fold process, including both biosecurity practices and wild bird deterrence measures. Deterrence includes scare devices, habitat modification, netting or even hiring a falconer to patrol the property.
“As you can imagine, keeping wild birds (and their feces) away is quite challenging and can be costly,” Wise said in an email.
Dr. Terry Lehenbauer, a veterinary professor at the University of California, Davis, said the situation is dynamic and could change any day, but that the restrictions to address the threat seem “adequate and appropriate.”
“I’m very confident that our milk and dairy product supply is very safe and wholesome,” said Lehenbauer, director of the school’s Veterinary Medicine Teaching and Research Center in Tulare.
Willis said early detection and monitoring are essential. He said monitoring needs to be a collaborative effort between public health officials and agricultural agencies at the state and federal levels.
“I’m not seeing this as any present danger to our community, or likely to be the start of the next pandemic, but it’s starting to get uncomfortably close,” Willis said.
