How does bird flu spread in cows? Experiment yields some ‘good news.’

Ever since scientists discovered influenza infecting American cows earlier this year, they have been puzzling over how it spreads from one animal to another. An experiment carried out in Kansas and Germany has shed some light on the mystery.

Scientists failed to find evidence that the virus can spread as a respiratory infection. Juergen Richt, a virus expert at Kansas State University who helped lead the research, said the results suggested that the virus is mainly infectious via contaminated milking machines.

In an interview, Richt said the results offered hope that the outbreak could be halted before the virus evolved into a form that could spread readily between humans.

“I think this is good news that we can most likely control it easier than people thought,” Richt said. “Hopefully, we can now kick this thing in the behind and knock it out.”

The findings have yet to be posted online or published in a peer-reviewed science journal.

Seema Lakdawala, a virus expert at Emory University who is researching the virus on dairy farms and was not involved in the new study, cautioned that breaking the transmission chain would require serious changes to how farmers milk their cows.

“It’s really great that these results are coming out,” she said. “But this is a real logistical problem.”

In January, veterinarians began to notice individual cows suffering mysterious declines in milk production. They sent samples to the Department of Agriculture for testing. In March, the department announced that milk from cows in Kansas, New Mexico and Texas contained a deadly strain of influenza that is widespread in birds. They also found the virus in swabs taken from the mouth of a Texas cow.

Since then, 132 herds in 12 states have tested positive for the virus. The cows suffer a drop in milk production and then typically recover, although some cows have died or have been slaughtered because they were not recovering.

Researchers have long known that some strains of influenza viruses can infect mammary cells in udders and can be shed in milk. But they had never seen an epidemic of bird flu circulating in cows as they have this year.

So far, state or federal officials have reported that only three people in the United States have been infected from the cows. Two of the infected farmworkers suffered conjunctivitis, otherwise known as pink eye. The third victim also experienced a cough and other respiratory symptoms.

The rapid spread of the virus among cows puzzled scientists. One possible explanation for the virus’s transmission was that it took advantage of how cows get milked on large farms. Workers clean a cow’s teats, squeeze them by hand to produce a few squirts then attach four tubes, known as a claw. When the claw is finished drawing out the cow’s milk, the worker removes it and places it on the next cow.

A claw will typically be used on hundreds of cows before it is cleaned.

In another study published Wednesday, Lakdawala and her colleagues found that the influenza virus could stay viable on a claw for several hours.

Scientists have also worried that the cows might be able to spread the virus as a respiratory disease. A cow with the virus in its airway would expel droplets as it breathed or coughed. Other cows might inhale the droplets, or pick them up by physical contact.

If that were the case, the virus might have the potential to attack cows that are raised for meat rather than milk. It might also allow the virus to spread more easily among humans.

In May, Richt and his colleagues in Kansas joined forces with German researchers to run experiments in which they deliberately infected cows. The two teams run high-level biosecurity facilities that can house animals as big as cows.

Martin Beer and his colleagues at the Friedrich-Loeffler-Institut in Greifswald, Germany, injected the virus into the teats of three lactating cows. Within two days, the animals developed clinical signs of infection much like what has been observed on farms: They got fevers, lost their appetites and produced far less milk.

What milk they did produce was thick. “It’s like yogurt coming out of the udder,” Beer said.

To see if the flu strain in the cows was significantly different from other strains infecting birds, Beer and his colleagues also injected cows with a different strain of the H5N1 bird flu virus. The cows suffered the same clinical signs of infection.

“So, this can happen anywhere where this virus is in the environment,” Richt said.