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Since scientists discovered influenza infecting U.S. dairy cows Earlier this yearpeople have been wondering how the virus spreads between animals. An experiment conducted in Kansas and Germany has solved the mystery.
Scientists failed to find evidence that the virus can be spread through respiratory infections. Jurgen Richter, a virologist at Kansas State University who helped lead the study, said the results suggest the virus is mainly transmitted through contaminated milking machines.
Dr. Richter said in an interview that the results give us hope that the outbreak can be contained before the virus evolves into a form that can be easily transmitted between people.
“I think the good news is that we may well be able to control this more than people think,” Dr. Richt said. “Hopefully we can beat it back now and eliminate it.”
The findings have not yet been posted online or published in a peer-reviewed scientific journal.
Seema Lakdawala, an Emory University virologist who studies the virus on dairy farms but was not involved in the new study, warned that breaking the chain of transmission would require farmers to make major changes to the way they milk their cows.
“It’s fantastic that these results are coming out,” she said. “But it’s really a logistical problem.”
In January, veterinarians began noticing a mysterious drop in milk production in individual cows. They sent samples to the Department of Agriculture for testing. Announce Cows in Kansas, New Mexico and Texas produced milk that contained a deadly flu virus that is widespread among birds. They also found the virus in a swab taken from the mouth of a cow in Texas.
since then, 132 herds in 12 states The cows’ milk production will drop and then usually recover, although some already dead Or they were slaughtered because they could not recover.
Researchers have Already known Some strains of flu can infect mammary cells in the udder and be spread through milk, but they have never seen an outbreak of bird flu in dairy cows like this year.
So far, state or federal officials have reported only three people infected with the bovine flu virus in the U.S. Two of the infected farm workers developed conjunctivitis, or pink eye. The third victim also had a cough and other respiratory symptoms.
The virus spread quickly among dairy cows, puzzling scientists. One possible explanation for the virus’s spread is that it takes advantage of the way milk is milked on large farms. Workers clean the cows’ teats and squeeze them by hand to extract a few streams of milk, which are then connected to four tubes, called “paws.” When the paw is done milking, workers remove it and put it on the next cow. One paw is often used on hundreds of cows before it is cleaned.
In another study In a study published on Wednesday, Dr. Lakdawala and her colleagues found that the influenza virus can survive on claws for several hours.
Scientists are also concerned that cows could spread the virus as a respiratory illness. Cows with the virus in their respiratory tracts would expel droplets when they breathe or cough. Other cows could inhale the droplets or become infected through physical contact.
If that’s the case, then the virus could attack cows that are raised for meat rather than milk. This could also make it easier for the virus to spread between people.
In May, Dr. Richter and his Kansas colleagues teamed up with German researchers to conduct an experiment to deliberately infect dairy cows. Both teams have high-level biosecurity facilities that can house animals as large as cows.
Martin Beer of the Friedrich-Loeffler Institute in Greifswald, Germany, and his colleagues injected the virus into the teats of three lactating dairy cows. Within two days, the cows showed clinical signs of infection, just as those observed on the farm: they had fever, loss of appetite, and a significant drop in milk production.
The milk they produce is thick, “like yogurt from the breast,” Dr. Beal said.
To determine whether the influenza virus strains that infected the cows were significantly different from those that infect other birds, Dr. Beal and his colleagues also injected cows with another strain of H5N1 avian influenza virus. The cows showed the same clinical signs of infection.
“So this could happen anywhere there’s this virus in the environment,” Dr. Richt said.
Dr. Richt also injected the bovine influenza virus into three non-milking cows and three bulls. Rather than injecting the virus into the cows’ udders, his team injected the virus into their mouths and noses.
The cows developed low-level infection and shed the virus from their noses and mouths for eight days.
Two days after infection, three healthy cows that had not been infected with the virus were placed in the same room as the sick cows. Over a period of 19 days, the scientists checked to see if the uninfected cows had also contracted the flu, either through contact with the sick cows or by inhaling their exhaled droplets.
None of the healthy cows became sick. “We saw no transmission,” Dr. Richt said. “This virus is not behaving like a typical respiratory influenza virus.”
He cautioned that the results from both experiments involved only a small number of cows. The scientists also studied earlier strains of the virus. Mutations Because it’s already spreading among animals, researchers can’t tell whether the most recent strain will be more like a respiratory illness.
Dr. Lakdawala said the new findings by researchers in Kansas and Germany are consistent with Epidemiological studiesadding more urgency to stopping the spread of the virus among dairy cows.
But that may be easier said than done. Sanitizing milking claws at every milking would reduce the farm’s milk production. Chemicals used to clean milking claws could also end up in the milk supply. “We don’t want bleach in our milk,” Dr. Lakdawala said.
She also said that in addition to stopping the virus from spreading among cattle, it was also crucial to protect people from the virus. “We don’t want these dairy workers to get infected,” she said.
In a typical milking parlor, cows stand on a platform so their udders are at eye level with workers. When milk splashes onto the platform, it can become droplets that fly into workers’ eyes or be inhaled. Personal protective equipment such as goggles and face masks can help block this route of infection.
Stopping the spread of the virus to dairy workers would not only protect their health, but also prevent the virus from gaining new opportunities to evolve within the human host and better adapt to humans.
“You never know what’s going to happen with this virus in the future,” Dr. Richt said.
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