Scientists have been trying to figure out how influenza spreads from animal to animal ever since they discovered influenza-infected cows in the United States earlier this year, and experiments in Kansas and Germany have solved the mystery.
Scientists could not find evidence that the virus spreads as a respiratory infection. Study leader Jurgen Licht, a virologist at Kansas State University, said the findings suggest the virus is primarily transmitted through contaminated milking machines.
In an interview, Dr. Licht said the findings offer hope that epidemics can be stopped before the virus evolves into a form that can easily spread between humans.
“I think the good news is that it’s likely easier to control than people thought,” Dr. Licht said. “Hopefully, we can kick this thing in the behind and beat it.”
The findings of this study have not yet been published online or in a peer-reviewed scientific journal.
Seema Lakdawala, a virologist at Emory University who studies viruses on dairy farms and was not involved in the study, warned that breaking the chain of infection will require major changes in the way dairy farmers milk their cows.
“It’s really great to see these results coming out,” she said, “but it’s really a logistical problem.”
In January, veterinarians began noticing mysterious declines in cows’ milk production. They sent samples to the USDA for testing. In March, the USDA announced that milk from cows in Kansas, New Mexico and Texas contained a deadly strain of influenza that spreads among birds. The virus was also found in swabs taken from the mouths of cows in Texas.
since then, 132 herds in 12 states Cows that test positive for the virus experience reduced milk production but usually recover. Dead Or they were euthanized because they did not recover.
The researchers Long known We know that some strains of influenza viruses can infect mammary gland cells in the udder and be shed in milk, but we’ve never seen bird flu spread among cows like we have this year.
So far, state and federal officials have reported only three people in the U.S. who have been infected by cows. Two of the infected farmworkers suffered from conjunctivitis, also known as pink eye. The third victim also experienced a cough and other respiratory symptoms.
Scientists were puzzled by how quickly the virus spread among cows. One of the reasons it was transmitted was through the way milking was done on large farms: workers clean the cow’s teats, milk her several times by hand, and then attach four tubes (called claws). When the claws are done with the cow’s milk, the worker removes them and attaches them to the next cow. A claw is typically used on hundreds of cows before it is cleaned.
another study In a paper published Wednesday, Dr Lakdawala and her colleagues found that the influenza virus can survive on fingernails for several hours.
Scientists are also concerned that cows could spread the virus as a respiratory disease: Cows with the virus in their respiratory tract expel droplets when they breathe or cough, and other cows can inhale the droplets or become infected through physical contact.
If so, the virus could attack cows raised for meat rather than milk, and it could also spread more easily among humans.
In May, Dr. Licht and his colleagues in Kansas collaborated with German researchers to deliberately infect cattle. The two teams run high-security facilities capable of housing animals the size of cows.
Martin Bier and his colleagues at the Friedrich-Löffler-Institut in Greifswald, Germany, injected the virus into the teats of three dairy cows. Within two days, the cows showed the same clinical signs of infection seen on farms: they had a fever, lost their appetite, and their milk production dropped dramatically.
The milk they produced was thick: “It was like yogurt coming out of the breast,” Dr. Beer said.
To see whether the cow flu strain was significantly different from others that infect birds, Dr. Beer and his colleagues also injected another strain of the H5N1 avian influenza virus into cows, who showed the same clinical symptoms of infection.
“So it can occur anywhere this virus is present in the environment,” Dr. Licht said.
Licht also injected the bovine flu virus into three non-lactating cows and three bulls: instead of injecting the virus into the udders, his team injected it into the animals’ mouths and noses.
The cows developed a mild infection and shed the virus from their noses and mouths for eight days.
Two days after infection, three healthy cows that didn’t have the virus were placed in the same room as the sick cows, and over a 19-day period, scientists studied whether the uninfected cows also contracted the flu through contact with the sick cows or by inhaling droplets exhaled by them.
None of the healthy cows became sick. “We have no confirmed infections,” Dr. Licht said. “This virus behaves differently than typical respiratory influenza viruses.”
He cautioned that the results of both experiments were based on small numbers of cattle. Scientists also studied earlier strains of the virus. The virus mutates as it moves from animal to animal, and researchers don’t know whether more recent strains cause symptoms like respiratory disease.
Dr Lakdawala said the new study, by researchers in Kansas and Germany, Epidemiological studiesThis adds to the urgency of preventing the spread of the virus in dairy cows.
But that may be easier said than done. Disinfecting milking claws after each cow would reduce a farm’s milk production. There’s also the risk that the chemicals used to clean the claws could contaminate the milk. “You don’t want bleach in your milk,” says Dr Lakdawala.
In addition to preventing cow-to-cow transmission, she said it’s also important to protect people from the virus. “We don’t want dairy workers to get it,” she said.
In a typical milking parlor, cows stand on a platform with their udders at eye level with the workers. If milk splashes onto the platform, it can splash into workers’ eyes or be inhaled. Personal protective equipment like goggles and face shields can help block that route of infection.
Preventing the spread of infection to dairy workers not only protects their health, it may also prevent the virus from evolving in humans and getting new opportunities to adapt to the human species.
“No one knows what the future holds for this virus,” Dr. Licht said.
