Since scientists discovered the flu in American cows earlier this year, they have been puzzled by how it spreads from one animal to another. An experiment in Kansas and Germany has shed some light on the mystery.
Scientists have failed to find evidence that the virus can spread as a respiratory infection. Jürgen Richt, a virologist at Kansas State University who helped lead the research, said the results suggest the virus is mainly transmitted through contaminated milking machines.
In an interview, Dr. Richt said the results offer hope that the outbreak can be stopped before the virus evolves into a form that can be readily transmitted among humans.
“I think the good news is that it’s easier to control than people think,” Dr. Richt said. “Hopefully now we can kick this thing in the rear and knock it out.”
The findings have not yet been published online or in a peer-reviewed scientific journal.
Seema Lakdawala, a virologist at Emory University who researches the virus on dairy farms and was not involved in the new study, warned that breaking the chain of transmission would require drastic changes in how farmers milk their cows.
“It’s great to see these results coming out,” he said. “But it’s a real logistical problem.”
In January, veterinarians began to notice a mysterious decline in individual cows’ milk production. The samples were sent to the Department of Agriculture for analysis. In March, the department announced that milk from cows in Kansas, New Mexico and Texas contained a deadly strain of influenza that had spread to birds. They also found the virus in swabs taken from the mouth of a Texas cow.
Since then, 132 herds in 12 states They have tested positive for the virus. Cows experience a drop in milk production, and then some cows usually recover are dead Or they are slaughtered because they don’t heal.
There are researchers Known for a long time Some strains of influenza viruses can infect mammary cells in udders and be shed in milk. But they have never seen bird flu spread to cows like this year.
So far, only three people in the U.S. have been infected by state or federal officials. Two of the infected farm workers developed conjunctivitis, also known as pink eye. A third victim also experienced coughing and other respiratory symptoms.
The rapid spread of the virus among cows has baffled scientists. One possible explanation for the spread of the virus is that large farms took advantage of how cows are milked. Workers clean a cow’s teats, squeeze them by hand, and produce a few scraps. When the claw has finished pulling out the cow’s milk, the worker removes it and places it on the next cow. A claw is usually used before cleaning hundreds of cows.
in another study Published on Wednesday, Dr. Lakdawala and his colleagues found that the influenza virus can remain viable in a fingernail for several hours.
Scientists are also concerned that cows may spread the virus as a respiratory disease. A cow with the virus in its respiratory tract will expel droplets when it breathes or coughs. Other cows may inhale the droplets or pick them up through physical contact.
If so, the virus is more likely to attack cows raised for meat than for milk. This allows the virus to spread easily between humans.
In May, Dr. Richt and his colleagues in Kansas teamed up with German researchers to conduct experiments that deliberately infected cows. Both groups run high-end biosecurity facilities that house large animals such as cows.
Martin Beer and his colleagues at the Friedrich-Löffler-Institut in Greifswald, Germany, injected the virus into the teats of three lactating cows. Within two days, the animals developed clinical signs of infection similar to those seen on farms: they developed fever, lost appetite and produced very little milk.
The milk they produced was thick. “It’s like curds coming out of the udder,” Dr. Beer said.
To see if the flu strain in cows was significantly different from strains affecting other birds, Dr. Beer and his colleagues injected cows with a different strain of the H5N1 bird flu virus. Cattle also experienced the same clinical signs of infection.
“So this virus can occur anywhere in the environment,” Dr. Richt said.
Dr. Richt administered cattle fever to three non-lactating female cows and three males. Instead of injecting the virus into the udders, his team injected the viruses into the animals’ mouths and noses.
The cows developed low-level infections and shed virus from their noses and mouths for eight days.
Two days after infection, three healthy cows without virus infection were placed in the same room as the sick one. Over 19 days, the scientists tested whether uninfected animals also developed fever by coming into contact with sick cows or breathing in droplets from them.
None of the healthy cows became ill. “We didn’t see a tradeoff,” Dr. Richt said. “The virus does not behave like a typical respiratory flu virus.”
He cautioned that the results of the two trials involved a small number of cows. The scientists also studied early strains of the virus. The virus changes from animal to animal, and researchers can’t say whether the latest strain will act like a respiratory disease.
Dr. Lakdawala said the new findings from researchers in Kansas and Germany are consistent. Epidemiological studiesAdded urgency was added to prevent the spread of the virus to dairy cows.
But that may be easier said than done. Disinfecting milking claws between each cow can slow down milking on farms. Chemicals used to clean nails can end up in the milk supply. “We don’t want bleach in milk,” said Dr. Lakdawala.
Besides preventing cow-to-cow transmission, it is essential to protect people from the virus, he said. “We don’t want these dairy workers to suffer,” he said.
In a typical milking parlor, cows stand on a platform so that their udders are at eye level for workers. When milk splashes on the platform, it becomes droplets that can fly into workers’ eyes or be inhaled. Personal protective equipment such as goggles and face shields can help prevent the path of infection.
Stopping the spread for dairy farmers doesn’t just protect their health. It could also prevent the virus from getting a new chance to evolve inside the human host and adapt to our species.
“You never know what will happen with this virus in the future,” Dr. Richt said.
