After three more flocks in California’s Central Valley tested positive for bird flu, questions have been raised about the true scale of the outbreak in the US, given inadequate or absent biosecurity and continued lack of testing.
The new cases, announced by U.S. Department of Agriculture (USDA) officials, bring to eight the total number of infected herds in California discovered this month.
“We’re really not testing enough,” said Meghan Davis, an associate professor at the Johns Hopkins Bloomberg School of Public Health. “The lack of testing has been one of the most shocking things to me in terms of watching the response to this outbreak.”
California is the 14th state to announce H5N1 cases in dairy cows since the outbreak was first identified in March. New Mexico and Michigan have also recently announced additional cases in dairy herds.
However, several states and municipalities have resistance to testing – among animals and people.
In Missouri, the first patient who tested positive without animal contact simultaneously became ill from a close contact, but the contact had not been tested for influenza and had not had a blood test done to check for H5N1 antibodies.
In Colorado, nine cases were discovered in July among 109 poultry workers who reported symptoms and consented to testing — just a fraction of the 663 workers exposed to H5N1-positive chickens, according to a recent report. report from the US Centers for Disease Control and Prevention (CDC).
The continued low level of testing, even among workers with confirmed exposure, underscores the limitations of federal agencies in responding to outbreaks.
Experts fear the virus is much more widespread than previously reported, and every new case discovered in an animal increases the risk of more people getting sick.
In California, farms near affected herds will collect bulk milk samples, Eric Deeble, USDA deputy undersecretary for marketing and regulatory programs, said Thursday.
Bulk milk testing can reveal cases in cows that appear healthy. After Colorado mandated this type of testing, officials found positive cases in 11 more herds.
“It would be really great if the U.S. Department of Agriculture would come up with some very strong recommendations” around initiatives like bulk milk testing, Davis said.
U.S. officials have considered bulk testing mandates “from day one” but have not instituted them, Deeble said in a phone call last month. He said Colorado’s successes were “probably unique to Colorado, and it’s not entirely appropriate to extrapolate them to the rest of the country.”
“Testing everything is a lot,” Steve Grube, chief medical officer of the Center for Food Safety and Applied Nutrition at the U.S. Food and Drug Administration (FDA), said at a briefing in August.
The USDA only requires H5N1 testing for dairy cows moving across state lines.
Deeble added that he had a “high degree of confidence” that existing testing accurately captured the status of animals moving between states, although intrastate movement was not as closely monitored. Still, he said, “I think the response is appropriate.”
It’s unclear how H5N1 got to California. The cases could point to a lapse in interstate testing, or the virus could have begun circulating before the order went into effect in April, or the virus could have jumped from cows to wildlife and then back to cows in California — or people and contaminated equipment, such as trucks, could have played a role.
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A June report from the U.S. Department of Agriculture (USDA) found that the virus most likely spreads through human activities, via undisinfected transportation between herds, through rearing and milking practices, or via contaminated clothing and equipment.
Other biosecurity deficiencies can include open-air dairies and practices such as washing cow barns with reused lagoon water that may be contaminated by other cows and wildlife. Large dairies also often send calves to “calf farms“where thousands of young cows from different states can be raised together and then sent back home or to other farms.
Sequencing of samples from the first three herds in California shows the virus is closely related to the strain circulating among dairy cows in other states, Deeble said Thursday — indicating the infections were not caused by a new spillover event from the bird flu strain that has been circulating among wild birds in North America since 2022.
The strain of the virus discovered in cows has also been found in other animals, including wild and domestic birds, cats and mice, which can then infect other animals with the virus adapted to cattle.
H5N1 vaccines are currently being tested for cows and are rolling off production lines in humans, although they have not yet been approved for use.
There have been no human cases reported in California and the state has a health warning for providers to watch for possible H5N1 cases in humans. No poultry farms have been affected by this outbreak, the state said in a proposition.
In June there was bird flu detected in San Francisco’s wastewater, but the source was unclear.
California is the nation’s largest dairy producer, accounting for 20 percent of U.S. milk production. A widespread outbreak could have significant consequences. economic effects for farmers – especially as the virus continues to circulate.
“Thinking about worker protections and worker guidelines is incredibly important,” Davis said. “Putting things in place now would be the most proactive way to go about it, and would be consistent with our principles of how we manage outbreaks, which is to be as aggressive as possible in the area of early detection and early response.”
Farm workers are at the highest risk of contracting the virus from sick animals. And if their illnesses — and the illnesses of the animals they care for — go undetected, it could pose new risks to others, Davis said.
“If this were to become known to the general public, we don’t know what we would see.”