by Without a sharp pivot in state and federal policies, the bird flu virus that has bedeviled American farms is likely to find a firm foothold among dairy cattle, scientists warn.
And that means bird flu could soon become a permanent threat to other animals and humans.
So far, this virus, H5N1, does not infect people easily, and the risk to the public remains low. But the longer the virus circulates in cattle, the more likely it is to acquire the mutations needed to offset a flu pandemic.
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“I think the window is closing on our ability to contain the outbreak,” said Dr. Krutika Kuppalli, an infectious disease doctor who worked at the World Health Organization until April.
“We’re so quick to blame China for what happened with SARS-CoV-2, but we’re not doing any better right now,” she said. “That’s how pandemics happen.”
Half a year after the outbreak, H5N1 shows no signs of abating in US dairy cattle or the workers who care for them. In recent weeks, the virus has spread into poultry and workers.
As of Wednesday, infections were reported in 192 cattle herds in 13 states, and in 13 people. There were nine workers on poultry farms near dairy farms in Colorado.
Earlier this month, the state reported that H5N1 was also diagnosed in six domestic cats, including two indoor cats with no direct exposure to the virus.
However, fundamental questions about the outbreak remain unanswered.
Researchers do not know how many farms are being investigated for the virus, how many cows are infected in each state, how and how often the virus jumps into humans and other animals, what the course of the illness is in humans and in animals and whether cows. can be infected more than once.
“We need to understand the extent of circulation in dairy cattle in the US, which we don’t have,” said Dr. Maria Van Kerkhove, acting director of pandemic preparedness and prevention at the WHO.
She praised the Department of Agriculture’s financial incentives to encourage farmers to cooperate with investigations but said “there is much more to be done”.
The government’s response to the outbreak could be complicated by the politics of an election year and the fact that oversight is being led by a federal department tasked with regulating and promoting the agricultural industry.
Federal officials have downplayed the risks to animals, saying the virus causes only mild illness in cows. But a study published in late July showed that cows on affected farms died at twice the normal rate and that some were infected without showing any symptoms.
In theory, nothing about this outbreak should make it difficult to contain, Van Kerkhove and other experts said. Unlike other flu viruses, this version of H5N1 does not appear to spread efficiently through the respiratory tract in cattle.
Instead, in most cases, infections appear to be transmitted through contaminated milk or viral particles on milking machines, vehicles or other objects, such as farm workers’ clothing.
“It’s really good news,” said Dr. Juergen Richt, a Kansas State University veterinarian and virus expert who led the study.
“If we want to control or eradicate this disease, we just have to focus on the mechanical transmission or the anthropogenic transmission,” he said.
Federal officials have said that results like these are based on the belief that they can stop the virus.
“I believe the answer is enough,” Eric Deeble, an official of the Department of Agriculture, told reporters on August 13.
He added that the outbreak can be contained because there is no wildlife reservoir of the virus – no species where it is naturally at home.
But experts outside the government disagreed, saying current measures were not enough to tackle the outbreak. The virus is endemic in wild birds, including waterfowl, and in a wide variety of mammals, including house mice, cats and raccoons.
“Wishful thinking is great, but it doesn’t necessarily get you the result you want,” said Michael Osterholm, an infectious disease expert at the University of Minnesota. “We are still in a state of confusion.”
Ideally, farms would “bulk test” pooled milk from many cows at once and restrict the movement of cattle and farm workers until the virus is eradicated.
But federal rules only require testing when cattle are moved between states. And in many states only visibly sick cows are required to be tested.
So far, Colorado is the only affected state to require bulk testing of milk, a decision that led to the identification of 10 additional infected herds within two weeks of the July 22 order.
The Department 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 are participating.
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 are staffed by migrant workers who fear deportation.
“Right now those men are feeling very vulnerable, and very few are willing to cooperate,” said Dr. Gregory Gray, a public health researcher on infectious diseases at the University of Texas Medical Branch. “Those who cooperate, in some cases, I think, regret that they cooperated.”
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 have blood drawn, two had antibodies to H5N1, indicating exposure to the virus.
Two-thirds of the milk samples from the farms showed signs of live virus, suggesting that infections in both animals and humans are more widespread than official counts suggest.
So far the virus has not appeared in cattle in other nations, perhaps because they do not move animals between farms on the scale that Americans do.
Genetic data suggest that the US outbreak originated from a single spill of the virus from birds into cattle and then spread to other parts of the country.
“At that time, there was a lot of virus in wild birds, but that seems to have quieted down, so there may not be another spill,” said Tom Peacock, a virus expert at the Pirbright Institute in Britain.
There is a slim chance that the virus will burn through susceptible cattle herds and disappear, at least for a while, scientists say. But it could take months or even years, if it happens at all.
The virus is more likely to become enzootic – endemic or rooted in animals – much like other viruses in pigs. Pig farms never rid themselves of a new virus, because susceptible piglets are constantly introduced into the population.
The same thing could happen among dairy cattle in the United States, Gray said: “Hopefully we never see on dairy farms what we see on pig farms, where you get different strains of flu that could be novel viruses mix and generate. “
Already the outbreak is imperiling livestock, poultry – and people.
The virus found in Colorado poultry farms appears to have originated from dairy cattle, resulting in the killing of 1.8 million birds. Nine workers involved in the killing became infected.
“If this continues at this level, the dairy industry will drown the poultry industry,” Peacock said.
“They have had every warning that this is a virus that could turn into a pandemic,” he said, referring to federal officials.
Pig farms usually have strict rules to contain new pathogens. Workers are not allowed to move between farms on the same day, for example, and must quarantine themselves between them. When they arrive, they have to shower and wear equipment provided by the farm.
Similar restrictions are likely to be more difficult to impose on dairy farms, as cows are kept alive longer and require much more space. But if dairy farms take these measures, “this is probably the way to control it,” Richt said.
Most experts said it would be premature, and probably not helpful, to immunize farm workers with current vaccines. But cattle vaccination may be a workable option.
It is easier to make animal vaccines more effective against viruses, with ingredients that may not be accepted in humans. “That gives me a little bit of hope,” said Troy Sutton, a flu expert at Pennsylvania State University.
However, it may not be possible to eliminate the outbreak by targeting cattle alone. Scientists have found the cattle version of the virus in black ponds in Texas, suggesting the birds could carry the virus to new farms.
“The idea that we’re going to have a flu pandemic anytime soon, I think the weight politically, economically, in terms of all of our mental health, is just too much to bear right now,” Van Kerkhove said.
“Everyone is tired from COVID, everyone is tired from mpox, everyone is tired from climate change and war and everything,” she said. “But right now, we don’t get tired.”
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