Cows and people are susceptible to H5N1 avian flu; scientists are still learning how the disease moves

Big cats can contract H5N1.
(Photo by M. Foskett, Unsplash)

Amid outbreaks of H5N1 avian flu in birds and other wildlife species, the disease has now infected cows and humans. "Texas health officials reported that an individual who had been in contact with cattle has contracted H5N1 avian flu, only the second case ever recorded in the U.S.," reports Helen Branswell of STAT. "The individual's only symptom is eye inflammation — infection of the conjunctiva, the tissue surrounding the eye. . . .The infected individual was treated with the influenza antiviral oseltamivir, sold as Tamiflu."

Confirmed H5N1 outbreaks in cattle have been reported in Texas, Kansas and Michigan, alongside presumed cases in New Mexico and Idaho. "The virus doesn't kill the cattle, but milk production is lowered, and the animals' feeding is reduced," Branswell explains. Previously, cows weren't considered susceptible to H5N1, which is deadly for birds and has been contracted by numerous mammals, including big cats, bears, foxes, donkeys, goats and dogs.

Earlier versions of H5N1 have proved more deadly for humans, but as the disease has evolved, it "seems to trigger human infections less frequently than earlier versions of the virus did. And when human cases caused by this strain occur, they are typically mild," Branswell reports. "But people who have studied influenza — and this virus in particular — for years do not know what to make of its movement into so many different animal species."

Richard Webby, an influenza virologist who heads the World Health Organization Collaborating Center for Studies on the Ecology of Influenza in Animals at St. Jude Children's Research Hospital in Memphis, Tenn., "called the infections in cows 'a head-scratcher,' saying he would not have figured cattle to be on the list of animals susceptible to this virus," Branswell writes. Webby added, "​​This particular version of H5 is teaching us a number of things we thought we knew weren't right."