Avian flu in US cows – a risk to humans?

The World Health Organization (WHO) currently considers the risk to humans to be low, but urges all countries to pay more attention to possible infections in animals and humans. Researchers fear that highly pathogenic bird flu viruses will continue to evolve as more birds and more mammals become infected around the world.

The WHO said it is investigating whether milk plays a role in transmission. He advised to consume only curdled milk and not to consume raw milk.

The USDA has, among other things, mandated that starting Monday, only dairy cows that test negative for bird flu can be transported from one US state to another. “It's a drop in the ocean,” Mike Worobe of the University of Arizona told Science.

“I am very surprised that cows are now infected,” said Martin Beer at the nationwide Friedrich Löffler Institute (FLI) in Greifswald. An infection test in 2006 concluded that cattle were “not at risk”. The virus is now “maximum” adapted to birds and The ability to affect humans is low.

But each new mammalian host could bring the virus a little closer to humans.

So far, only one case of cow-to-human transmission has been known in the United States, and they also only developed conjunctivitis. But Beer points to the many undocumented workers in the U.S., “especially on cattle farms.” Since 2021, WHO has recorded a total of 28 bird flu infections in humans.

Evolutionary biologist Worobe still sees future dangers. “We are in uncharted territory as a mammalian-adapted H5N1 virus spreads in land mammals for the first time, with hundreds of thousands of people coming into contact every day,” he said, referring to the situation in the United States. The next pandemic virus will come from a situation like this, he suspects.

Martin Schwemle, a virologist at the University Hospital of Freiburg, said the presence of very high levels of the virus in the milk of infected cows is problematic. The virus is spread through every infectious drop of milk that enters the environment – and thus through the equipment used in milk production.

I believe it is very difficult to control such widespread pollution.

According to Schwemmle, there is still no evidence of dairy cows being infected with the virus in Europe. However, this can change at any time if it comes from America or originates in Europe itself. According to FLI researcher Beer, there is a lot of attention on this subject in Germany.

Officials know that H5N1 should also be considered and, in some circumstances, tested for if there are any unexplained illnesses in cow herds and low milk production.

Beer points to an overall better control system. “In Germany we actually have a glass cow. Every animal is clearly marked and every animal's movement can be traced through a database. Not so in America.”