H5N1 has killed tens of millions of birds and thousands of mammals worldwide since 2020 in an unprecedented outbreak.
It is still unclear how the virus originated first jumped on cattlebut many believe the most likely route of infection is through wild birds, which have been found dead on some US farms.
Its apparent ability to spread within cows is of particular interest, because with each new mammal that jumps H5N1, it has more opportunities for the virus to evolve — and possibly to better infect humans.
So far this year, there have been two confirmed cases of H5N1 in humans.
In Vietnam, a man died in March after direct contact with an infected bird, while in Texas a farm worker contracted the virus from sick livestock – although his symptoms were mild.
A spokesperson for the Center for Disease Control said last week that they are monitoring an additional 44 people exposed to the virus through livestock for signs of infection.
The WHO considers the risk to humans to be lowbut urged countries to quickly share information to enable real-time monitoring of the situation to ensure preparedness as the virus continues to spread.
It also warned on Tuesday that there was a risk of H5N1 jumping from migratory birds to livestock in countries outside the US.
“With the virus being spread around the world by migratory birds, there is certainly a risk of cows in other countries becoming infected,” Wenqing Zhang, head of the agency's Global Influenza Program, told reporters in Geneva.
A government spokesperson said: “These reports do not change the animal risk level for Britain, which is currently 'low' and we have no reason to suspect the virus is circulating among our livestock, nor is this strain of virus circulating in Europe.
“The advice from the Food Standards Agency remains that bird flu poses a very low food safety risk to UK consumers.”
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