A person in the US has contracted bird flu from infected dairy cows in Texas. This is the first confirmed case of a subtype of the virus, named H5N1, transmitting between a human and another mammal.

The US Centers for Disease Control and Prevention (CDC) announced the news today after confirming the positive test results over the weekend. The person, whose only symptom is eye inflammation, is on antiviral medications and recovering. They had been exposed to cows believed to be infected with the virus, which has decimated global bird populations.

Last week, cows across five US states – Texas, Kansas, Michigan, New Mexico and Idaho – tested positive for H5N1. It is unclear how they became sick, but it now seems that the virus may be spreading among the animals, according to the US Department of Agriculture.

Previously, mammals had only been confirmed to contract the virus from sick birds. “There have been a couple of outbreaks that didn’t include humans where it is possible there was mammal-to-mammal transmission,” says Richard Webby at St. Jude Children’s Hospital in Tennessee. For instance, 17,000 baby elephant seals died from bird flu in Argentina late last year. There was also an outbreak among farmed mink in Spain in 2022. But it is hard to rule out the possibility of other sources of the virus such as contaminated food in these situations, he says.

Despite the recent human infection, the CDC says the risk of contracting bird flu remains low for most people. People in close contact with infected birds or other animals, including livestock, have the greatest risk. While pasteurised milk remains safe, people should avoid consuming or handling raw milk products.