U.S. dairy farm worker infected as bird flu spreads to cows in five states
Unexpected H5N1 outbreaks in cattle raise difficult questions about how to protect herds and people
U.S. dairy farm worker infected as bird flu spreads to cows in five states
Contaminated water or feed may have caused U.S. dairy cows to become infected with the H5N1 avian influenza virus.
Texas officials today issued a “health alert” about the first confirmed case of a human infection with a bird influenza virus that has found its ways into dairy cows. The worker developed conjunctivitis, a mild eye infection that frequently occurs when avian influenza viruses jump into humans.
The case is the latest surprise in the global march of the flu strain, a subtype of H5N1 known as clade 2.3.4.4b that has devastated wild birds and poultry around the world for more than 2 years. The U.S. Department of Agriculture (USDA) says it has confirmed the virus has infected cattle at farms in Texas, Kansas, New Mexico, and Michigan, while Idaho has a “presumptive” outbreak at one dairy farm. Wild birds, which have been found dead on some farms, most likely contaminated cow feed or water.
Some evidence suggests the virus was transmitted between cows, but that remains unproven. And for now, USDA says its “initial testing has not found changes to the virus that would make it more transmissible to humans.” Still, the widespread occurrence of H5N1 in mammals has renewed worries that it may evolve to become more transmissible between people. And scientists are urgently trying to answer a host of questions, including how far the virus has spread among U.S. cows and how to prevent more herds and people from becoming infected.
Although cows routinely contract influenza viruses, this is the first time that a “highly pathogenic” bird flu strain has been found in them. USDA says about 10% of affected herds have become ill. Sick cows have a mild illness, and produce less milk, which is thicker than usual, resembling colostrum, the first milk produced after a calf is born.
USDA today stressed that the “current risk to the public remains low.” Contamination of commercial milk is of “no concern,” the agency said in a statement, because pasteurization reliably kills viruses, and milk from sick cows is not being sold. The U.S. Centers for Disease Control and Prevention (CDC) says people should not drink raw milk or eat products such as cheese that are made from it. The USDA statement noted that cats on farms have also become infected.
Antibody tests of herds should soon reveal how widespread the infection is and how long it has been infecting cattle. Lab experiments may clarify how a virus that typically causes respiratory disease wound up in cow udders, making it detectable in their milk, and whether other organs are infected. No evidence exists that the virus has infected beef cattle, but researchers say that could simply be because of a lack of surveillance, or because these animals show subtler symptoms than changes in milk production and its appearance.
Texas Health and Human Services said the infected person was tested for flu “late last week” and that CDC confirmed it was the bird flu virus this weekend. The person is being treated with oseltamivir, an antiviral drug. “We need to be advocating for our employees on these farms, providing them support and education in whatever language that it needs to be in,” says Joe Armstrong, a bovine veterinarian who works with the University of Minnesota (UM) Extension. Dairy workers rarely wear protective gear, such as masks and goggles, Armstrong says. In the “dairy parlors” that commercial farms use to milk cows, floors are often cleaned using high-pressure water sprayers, which could aerosolize the virus, he notes.
Although avian influenza viruses, first detected in humans in 1997, have caused outbreaks that killed hundreds of people, they have difficulty infecting human cells because of differences in the sugars that adorn human and bird cellular receptors for the virus. But humans have the bird version in our eyes, which explains why we can develop conjunctivitis.
“I think the conjunctivitis in itself is not so serious, but it points to the fact that those people have been exposed and that they might develop respiratory disease,” says Thijs Kuiken, a comparative pathologist at Erasmus Medical Center who specializes in avian influenza. “I am really concerned about the people who are looking after affected cattle because I’ve heard of really high levels of virus in the milk and people are milking these animals twice a day.”
The appearance of H5N1, clade 2.3.4.4b in cows was unexpected, even after its detection in dozens of mammalian species, including cats, dogs, foxes, tigers, leopards, coyotes, bears, seals, dolphins—and, last month, goats at a Minnesota farm that also had an infected poultry flock. Cattle are often infected with type D, which one study shows can readily infect farm workers and cause disease, but H5N1 is a type A virus. “It’s definitely taken me by surprise, but perhaps it shouldn’t have,” says virologist Richard Webby of St. Jude Children’s Research Hospital.
Idaho officials contend transmission of the virus between cattle occurred on a dairy farm there. That herd became sick after coming into contact with cows trucked in from an area in Texas where the virus was circulating. That “does lead state officials to believe cow-to-cow is how the virus was transmitted in this case,” a spokesperson for the Idaho State Department of Agriculture told Science. In Michigan, too, the virus surfaced after the importation of cows from Texas.
An experiment published in 2006 demonstrated that a different H5N1 clade could infect calves. Virologist Martin Beer of the Friedrich Loeffler Institute, who led that study, says “very special circumstances” might explain the spread of the virus in U.S. cattle, including the way the animals are milked or as-yet-undetected genomic adaptations in the virus. “We need to wait for much better epidemiological data,” Beer says.
The good news is that so far, mammals infected with clade 2.3.4.4b have rarely seen sustained transmission, Webby notes. “Putting it into context, I’m not sure at this stage that [the cattle infections are] much different than any other mammal infections,” he says.
There have been about a dozen reports worldwide of an H5N1 virus from that clade infecting humans, all of whom had had direct contact with birds, including one case in the United States in August 2022, in a worker who had culled infected poultry.
A major question now looming is how to prevent further spread from dairy farms. Most countries, including the U.S., require culling of entire poultry flocks if even a single bird is infected with a highly pathogenic avian influenza virus. But there is no talk of culling cows, which cost up to $2500 each and are not becoming seriously ill.
There are no H5N1 vaccines for cattle. Poultry vaccines do exist and are used heavily in China, with some marked successes. A crash program to develop a cattle equivalent might make sense, says Carol Cardona, an avian influenza specialist and poultry veterinarian at UM Twin Cities. If vaccinations can reduce viral spread, they might offer some secondary protection to dairy workers. “The person-to-cow ratio is so much higher than the person-to-chicken ratio,” notes Cardona, putting many more workers at risk. The cattle infections are “a game changer,” she adds. “I think it’s all hands on deck.”
David Swayne, who formerly ran USDA’s avian influenza research lab, says it would be possible to quickly make a new cattle vaccine by modifying one now used in swine. And unlike the bird vaccines, which are banned in the U.S. due in part to international trade concerns, swine vaccination is already “widely accepted,” Swayne says.
The U.S. government stockpiles an H5N1 vaccine for humans, and CDC said in a statement today that vaccines developed for related viruses “are available for vaccine manufacturing” if preliminary studies show they protect against 2.3.4.4b. “As a protective measure you can imagine vaccinating dairy workers,” Kuiken says.
The human infection in Texas has echoes of a massive outbreak of another highly pathogenic avian influenza virus, H7N7, in poultry flocks in the Netherlands in 2003 that Kuiken studied. Hundreds of people developed conjunctivitis, mainly during culling of infected flocks, and there was some evidence of human-to-human transmission. One veterinarian died.
Kuiken advises the U.S. to restrict the movement of cattle to limit the spread of the virus. “I would take the precautionary principle and say, ‘OK, until we know what’s going on, let’s put a standstill on this,’” he says.
But that is a controversial idea because the dairy industry relies on trucking cows south over the winters and then returning them north. And Armstrong doubts halting cattle transports would have much impact if migratory birds prove to be the main route of transmission. Many bird species are currently moving north and may be taking the virus with them. “It would be very surprising if it wasn’t already everywhere,” Armstrong says, noting how difficult it is for farms to keep out birds. “We have to protect people, but we also have to … make sure we’re not crippling the industry,” he says.
As to H5N1’s future, Cardona says we should continue to expect the unexpected. “The virus is making up new dances,” she says. “It’s broken the rules on everything.”
SOURCE-https://www.unmc.edu/healthsecurity/transmission/2024/04/02/u-s-dairy-farm-worker-infected-as-bird-flu-spreads-to-cows-in-five-states/#:~:text=The%20U.S.%20Department%20of%20Agriculture,contaminated%20cow%20feed%20or%20water.
