This story was updated after California confirmed bird flu in three cow herds.
On Thursday, the California Department of Food and Agriculture announced it is investigating the possible introduction of H5N1 bird flu in cattle at three dairy farms in the Central Valley. On Friday, it confirmed the first known bird flu cases in that state.
In a statement Thursday, officials said testing of samples from the three farms was underway in the state’s veterinary diagnostic lab. After preliminary testing, the samples were sent to the U.S. Department of Agriculture veterinary lab, which confirmed they were positive for bird flu, the state said Friday. California is the 14th state to report an infection of bird flu in dairy cows.
The state said the dairy herds “began showing clinical signs” consistent with bird flu on August 25.
California, the nation’s largest milk producer, is home to roughly 1.7 million dairy cows. Nearly 90% of them live in the San Joaquin Valley, a vast stretch of fertile farmland that extends more than 250 miles from Stockton to Bakersfield. Dairy farms there tend to be big operations, separated from each other by significant distances, and for months farmers have been taking extra precautions like bleaching down cow-toting trailers to reduce cross-contamination.
Workers there are usually dedicated to just one herd, unlike in Colorado and Michigan, where workers sometimes pick up shifts both at dairy farms and nearby poultry operations, creating additional biosecurity challenges. In both states, which have seen double-digit outbreaks, infections at dairy farms have spilled over to poultry sites, according to genetic analyses of the virus.
But despite those measures, many have feared that with the lackluster national response to the outbreak, sooner or later H5N1 bird flu would come for California. “It seemed like it might be only a matter of time,” said Terry Lehenbauer, a bovine disease epidemiologist and professor emeritus at the University of California, Davis.
California is the first new state since Wyoming announced it had found the virus in one herd on June 7. Last month, Oklahoma confirmed the presence of the virus in two herds, but samples from those animals were actually collected back in April and were not submitted for testing until after the USDA began offering farmers financial compensation for lost milk production at the beginning of July.
The program is part of an $824 million USDA effort to bolster broader testing and surveillance for the bird flu on dairy farms, which also includes a voluntary pilot program for farms to proactively test samples from bulk milk tanks on a weekly basis. If herds show no sign of H5N1 for three weeks, farmers participating in the pilots can freely move cattle across state lines without having to test individual animals.
But both programs have seen limited uptake by the dairy industry. As of Wednesday, just 33 herds were being regularly monitored nationally as part of the USDA pilot program, including one herd in California.
A spokesman for the CDFA did not respond to STAT’s questions about how much testing California has performed since the start of the U.S. outbreak in late March or how the three farms were identified.
“At the end of the day it all has to do with how many herds have been tested,” said Lehenbauer. “There hasn’t been as much testing as we might like from a scientific or medical perspective.”
Colorado, which currently leads the nation in most reported herds, is also the only state that has mandated all dairy farms submit weekly milk samples from their bulk tanks for testing. In the weeks after that order went into effect on July 22, an additional 11 infected herds were discovered through bulk milk tank testing. The program has allowed officials there to get a more accurate picture of how the virus is traveling and alert farmers early, so they can isolate animals before the infection sweeps through their entire herd.
In unpublished research, scientists at Colorado State University and Iowa State University who tested bulk milk tank samples found that the virus is detectable 14 to 16 days before farms saw a significant increase in symptoms like low appetite, lethargy, fever, and a dropoff in milk production.
That’s why the most important time to test is in the two to three weeks before clinical signs appear, said Keith Poulsen, a professor of large animal internal medicine at the University of Wisconsin-Madison and the director of the Wisconsin Veterinary Diagnostic Laboratory. “By the time you see them, you can’t do anything about it.”
But so far, no other states have followed Colorado’s lead. Since June, Iowa has enacted a more limited surveillance protocol — mandating that dairy farms within 20 kilometers (12.4 miles) of an infected poultry operation submit weekly samples from bulk tanks and any sick animals for testing. Along with Minnesota and Wisconsin, Iowa is also requiring testing of lactating cattle prior to showing them at state and county fairs.
Elsewhere, and outside of those circumstances, states are largely leaving the decision to test up to farmers. And a coordinated effort to conduct mandatory surveillance at the national level has yet to materialize.
“We’ve been told to be ready to do large-scale surveillance through bulk milk tank testing multiple times since May.” Poulsen said. “For some reason or another, it has just never come to fruition.”
A USDA spokesperson told STAT via email that the network of veterinary diagnostic labs cleared to test for H5N1 was evaluated to make sure there was enough capacity to handle a surge in voluntary surveillance testing, but that there is currently no plan for government-mandated bulk milk tank testing at the national level.
Decisions on mandating bulk milk testing “ultimately lie with each individual state,” the spokesperson said, adding that the agency is appreciative of Colorado’s order, as it allows the USDA to better understand where the virus is and “take additional steps to protect animal health as well as farmers, farm workers, and their communities.”
But Poulsen said the lack of a coordinated effort to extend that kind of testing nationwide is a missed public health opportunity, both for animal and human health. “We’ve built a system that could respond to infectious outbreaks like this but we’re not really using it,” he said. “It’s baffling.”
