(Bloomberg) -- Dairy workers remain at risk for the H5N1 bird flu that’s spreading in cows and should wear protection to ward off the virus, US health officials said as they released details on one worker who experienced an eye infection.  

The dairy worker underwent genetic testing of samples from both eyes and his nose, according to a letter to the New England Journal of Medicine from the US Centers for Disease Control and Prevention’s Tim Uyeki and Texas health officials, which confirmed the presence of the virus.

The highly contagious strain of avian flu has spread across dairy cattle in 36 herds across nine states this year, and the US Food and Drug Administration said it found fragments in one out of every five commercial milk samples tested. The US Department of Agriculture is testing beef for the presence of H5N1 because of concerns about potential spread to humans. Pasteurized milk and cooked beef are safe to consume, the FDA has said.

Dairy workers remain at highest risk and are urged to wear protective equipment and wash their hands regularly, the letter said. The worker who contracted H5N1 and their close contacts were prescribed an oral antiviral. The day after he was tested, the worker reported no symptoms other than discomfort in the eyes, probably due to swelling.

H5N1 has long been spreading in birds, although in a number of forms with varied potential to infect  other species. The virus found in the worker had a mutation that has been associated with infections in mammals and detected previously in humans, the researchers said. 

Still, the pathogen in both the man and the cattle primarily maintained its avian genetic characteristics and didn’t show changes that would make it easier to latch onto people or transmit to humans, the researchers found. There was no suggestion the virus had any resistance to antiviral drugs used to treat it.

H5N1 has pandemic potential, the CDC noted, and there are two potential vaccine candidates that show potential to prevent it. Only 26 confirmed cases of bird flu in humans have been reported by the World Health Organization from 2020 to this February.

--With assistance from Michelle Fay Cortez.

(Adds genetic analysis from fifth paragraph.)

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