Scientists warn that without rapid changes in course at the state and federal levels, the bird flu virus ravaging American farms is likely to spread to dairy cattle as well.
This means that bird flu could soon become a permanent threat to other animals and people.
So far, this virus, H5N1, is not infecting humans very easily, and the risk to the public remains low. But the longer the virus circulates in livestock, the greater the chance that it will acquire the mutations needed to cause an influenza pandemic.
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“I think the window for our ability to contain the outbreak is getting smaller and smaller,” said Dr. Krutika Kuppalli, an infectious disease doctor who worked at the World Health Organization until April.
“We are so quick to blame China for what happened with SARS-CoV-2, but we are not doing any better at the moment,” she added. “That is how pandemics happen.”
Six months after the outbreak, H5N1 shows no signs of abating in U.S. dairy cattle or the workers who care for them. In recent weeks, the virus has spread to poultry and workers.
As of Wednesday, infections had been reported in 192 herds of cattle in 13 states and in 13 people. Nine were workers on poultry farms near Colorado dairy farms.
Earlier this month, the state reported that H5N1 had also been detected in six domestic cats, including two indoor cats that had not been directly exposed to the virus.
Yet fundamental questions about the outbreak remain unanswered.
Researchers do not know how many farms are testing for the virus, how many cows are infected in each state, how and how often the virus jumps to humans and other animals, how the disease progresses in people and animals, or whether cows can be infected more than once.
“We need to understand the extent of circulation among dairy cattle in the US, but we don’t,” said Dr. Maria Van Kerkhove, acting director of pandemic preparedness and prevention at WHO.
She praised the Department of Agriculture’s financial incentives to encourage farmers to participate in research, but said “much more needs to be done.”
The government’s response to the outbreak could be complicated by the politics of an election year and the fact that it is overseen by a federal agency charged with both regulating and promoting the agricultural sector.
Federal officials have downplayed the risks to animals, saying the virus causes only mild illness in cows. But a study published in late July found that cows on affected farms died at twice the normal rate and that some were infected without showing any outward symptoms.
In theory, nothing about this outbreak should make it difficult to contain, Van Kerkhove and other experts said. Unlike other influenza viruses, this version of H5N1 does not appear to spread efficiently through the respiratory tract of livestock.
In most cases, however, infections appear to be transmitted through contaminated milk or virus particles on milking machines, vehicles, or other objects, such as the clothing of farm workers.
“It’s actually good news,” said Dr. Juergen Richt, a veterinarian and virus expert at Kansas State University who led the study.
“If we want to control or eradicate this disease, we only need to target mechanical transmission or anthropogenic transmission,” he said.
Federal officials say such findings support the belief that they can stop the virus.
“I believe the response has been adequate,” Eric Deeble, an Agriculture Department official, told reporters on Aug. 13.
He also said that the outbreak is under control because there is no wildlife reservoir where the virus naturally feels at home.
But experts outside the government disagreed, saying current measures were not enough to stop the outbreak. The virus is trapped in wild birds, including waterfowl, and in a wide range of mammals, including house mice, cats and raccoons.
“Wishful thinking is a wonderful thing, but it doesn’t necessarily get you the results you need,” said Michael Osterholm, an infectious disease expert at the University of Minnesota. “We’re still in a state of total confusion.”
Ideally, farms would bulk test milk from multiple cows at a time and restrict the movement of livestock and farm workers until the virus is eradicated.
But federal rules require testing only when cattle are moved between states. And many states require testing only for cows that are visibly sick.
So far, Colorado is the only affected state to require large-scale milk testing, a move that led to the identification of 10 additional infected herds within two weeks of the July 22 order.
The Ministry of Agriculture has also tried to encourage testing through a voluntary program. Of the approximately 24,000 farms that sell milk in the country, only 30 participate.
The program has resulted in the identification of herds with infected cows and is “an indication that the system is working as intended,” a department spokesperson said in an emailed statement.
Given the risk to their businesses, few farm owners have accepted offers of compensation to set up testing or biosecurity. Many employ migrant workers who fear deportation.
“Right now, these guys feel very vulnerable and very, very few are willing to cooperate,” said Dr. Gregory Gray, an infectious disease and public health researcher at the University of Texas Medical Branch. “Those who do cooperate, I think in some cases, regret it.”
Gray and his colleagues visited two Texas farms in April that had reported sick cattle in the previous 30 days. Of the 14 workers who agreed to be blood drawn, two had antibodies to H5N1, indicating exposure to the virus.
Two-thirds of the milk samples from the farms showed evidence of live virus, suggesting that infections in both animals and humans are more widespread than official counts indicate.
So far, the virus has not shown up in cattle in other countries, perhaps because animals are not moved between farms on the same scale as in the US.
Genetic data suggests the US outbreak resulted from a one-time transfer of the virus from birds to livestock that then spread to other parts of the country.
“There was a lot of virus in wild birds at the time, but that seems to have decreased now, so there may not be another spillover,” said Tom Peacock, a virus expert at the Pirbright Institute in Britain.
There is a small chance that the virus will burn through susceptible herds and disappear, at least for a while, scientists say. But that could take months or even years, if it happens at all.
More likely, the virus will become endemic — endemic or rooted in animals — just as other viruses are in pigs. Pig farms never get rid of a new virus because susceptible pigs are continually being introduced into the population.
The same thing could happen in dairy cattle in the United States, Gray said: “What we’re seeing on pig farms is something we hope we never see on dairy farms, where you get multiple strains of influenza that can mix and generate new viruses.”
The outbreak in cattle is already endangering poultry and humans.
The virus found on Colorado poultry farms was found to have originated from dairy cattle and resulted in the culling of 1.8 million birds, infecting nine workers involved in the slaughter.
“If this continues, the dairy industry will drive the poultry industry into the ground,” Peacock said.
“They’ve had every possible warning that this is a virus that could become a pandemic,” he added, referring to federal officials.
Pig farms generally have strict rules to contain new pathogens. For example, workers are not allowed to move from farm to farm on the same day and must quarantine themselves in between. Upon arrival, they must shower and wear clothing provided by the farm.
Imposing similar restrictions on dairy farms will likely be harder, since cows are kept longer and require much more space. But if dairy farms take these measures, “this will most likely be the way to get it under control,” Richt said.
Most experts said it would be premature, and probably not helpful, to vaccinate farmworkers with current vaccines. But vaccinating livestock could be a viable option.
It’s easier to make animal vaccines more effective against a virus, with ingredients that might not be tolerated by humans. “That makes me somewhat optimistic,” said Troy Sutton, an influenza expert at Pennsylvania State University.
Still, it may not be possible to stop the outbreak by focusing on livestock alone. Scientists have found the livestock version of the virus in blackbirds in Texas, suggesting that the birds could carry the virus to new farms.
“The idea that we might soon have a flu pandemic is too much to bear at the moment, both politically and economically, and in terms of our mental health,” said Van Kerkhove.
“Everybody’s tired of COVID, everybody’s tired of mpox, everybody’s tired of climate change and war and all of that,” she added. “But right now, we can’t be tired.”
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