Ever since scientists discovered the flu infecting American cattle earlier this year, they have puzzled over how it spreads from one animal to another. An experiment conducted in Kansas and Germany shed light on the mystery.
Scientists have failed to find evidence that the virus can spread as a respiratory infection. Juergen Richt, a virologist at Kansas State University who helped lead the research, said the results suggested the virus was primarily 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 easily spread between people.
“I think it’s good news that we can probably control it more easily than people thought,” said Dr. Richt. “Hopefully we can kick this thing in the rear and knock it out.”
The findings have not yet been posted online or published in a peer-reviewed science 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 transmission chain would require serious changes in how farmers milk their cows. .
“It’s really great that these results are coming out,” he said. “But it’s a real logistical problem.”
In January, veterinarians began noticing individual cows suffering mysterious drops in milk production. They sent samples 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 is prevalent in birds. They also found the virus in swabs taken from the mouth of a Texas cow.
Since, 132 flocks in 12 states tested positive for the virus. Cows suffer a drop in milk production and then usually recover, even some cows died or killed because they do not heal.
Researchers have long known that some strains of influenza viruses can infect the mammary cells in the udders and can be shed in the milk. But they have never seen an epidemic of bird flu spread among cattle like they are experiencing this year.
So far, state or federal officials have reported that only three people in the United States have been infected by cattle. Two of the infected farm workers suffered from conjunctivitis, otherwise known as pink eye. The third victim also experienced a cough and other respiratory symptoms.
The rapid spread of the virus among cattle has surprised scientists. One possible explanation for the transmission of the virus is that it took advantage of how cows are milked on large farms. Workers clean the cow’s teats, squeeze them by hand to produce several squirts then attach four tubes, known as claws. When the cow has finished milking the cow, the worker will remove it and put it on the next cow. A claw is usually used on hundreds of cows before it is cleaned.
Others study published on Wednesday, Dr. Lakdawala and his colleagues found that the influenza virus can remain viable on a fingernail for several hours.
Scientists are also concerned that cattle could spread the virus as a respiratory disease. A cow with a respiratory virus will produce droplets as it breathes or coughs. Other cows may inhale the droplets, or pick them up through physical contact.
If that’s the case, the virus may have the potential to attack cows raised for meat rather than milk. It may also allow the virus to spread more easily between people.
In May, Dr. joined forces. Richt and his colleagues in Kansas with German researchers to run experiments in which they deliberately infected cows. The two teams operate high-level biosecurity facilities that can house cattle-sized animals.
Martin Beer and his colleagues at the Friedrich-Loeffler-Institut in Greifswald, Germany, injected the virus into the breasts of three lactating cows. Within two days, the animals had clinical signs of infection similar to what is observed on farms: They developed fever, lost appetite and produced less milk.
The milk they made was thick. “It’s like yogurt coming out of the udder,” says Dr. Beer.
To see if the strain of influenza in cattle is significantly different from other strains that infect birds, Dr. Beer and his colleagues also injected cows with a different strain of the H5N1 bird flu virus. The cattle suffered the same clinical signs of infection.
“So this can happen anywhere that this virus is in the environment,” said Dr. Richt.
Dr. also injected. Richt the cow flu in three female cows that are not lactating, and also in three males. Instead of injecting the virus into the udders, his team injected the viruses into the animals’ mouths and noses.
The cows had a low level of infection, and they 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 ones. Over the course of 19 days, the scientists tested whether the uninfected animals also contracted the flu, whether through contact with sick cows or breathing in the droplets they released.
None of the healthy cows got sick. “We didn’t see the transmission,” said Dr. Richt. “The virus does not behave like a typical respiratory influenza virus.”
He cautioned that the results from the two experiments involved a small number of cows. The scientists also studied an early strain of the virus. The virus mutates as it moves from animal to animal, and researchers can’t say whether a more recent strain will be more like a respiratory disease.
said Dr. New findings from researchers in Kansas and Germany, consistent with epidemiological studiesadded more need to stop the spread of the virus in dairy cows.
But that may be easier said than done. Disinfecting the milking hooves between each cow will slow down milking on farms. Chemicals used to clean nails can also end up in the milk supply. “We don’t want bleach in milk,” says Dr. Lakdawala
In addition to stopping the spread from cow to cow, he also said it is important to protect people from the virus. “We don’t want these dairy workers to get infected,” he said.
In a typical milking parlor, the cows stand on a platform so that their udders are in view of the workers. When milk splashes on the platform, it can become droplets that can fly into workers’ eyes or be inhaled. Personal protective equipment such as goggles and face shields can help block the route of infection.
Stopping the spread among dairy workers will not only protect their health. It may also prevent the virus from having a new chance to evolve within the human host and better adapt to our species.
“You never know what will happen with this virus in the future,” said Dr. Richt.
