Tests done on a Chilean man infected with bird flu showed signs that the virus has partially adapted to spread between mammals. However, the public health risk still remains low, U.S. health officials say.
“Those genetic changes have been seen previously with past H5N1 infections, and have not resulted in spread between people,” Vivien Dugan, acting director of the influenza division at the U.S. Centers for Disease Control and Prevention National Center for Immunization and Respiratory Diseases, told The New York Times. “Nevertheless, it’s important to continue to look carefully at every instance of human infection, as well as other mammalian spillover events, and to track viral evolution in birds.”
While the two mutations seen in the PB2 gene can help the virus replicate in mammals, the samples did not have other genetic changes that would enable the virus to stabilize and bind tightly to human cells, according to the CDC.
“There are three major categories of changes we think H5 has to undergo to switch from being a bird virus to being a human virus,” Richard Webby, a bird flu expert at St. Jude Children’s Research Hospital in Memphis, Tennessee, told The Times. “The sequences from the person in Chile have one of those classes of changes. But we also know that of those three sets of changes, this is the easiest one for the virus to make.”
No other cases have been linked to the man infected with the H5N1 virus. His case began with a cough and a sore throat, according to the World Health Organization, which received a report of the man’s illness on March 29 from the Chile Ministry of Health. Although it is not known how the 53-year-old man was infected, there have been cases in birds and sea lions in the region where he lives. The man remains hospitalized. Public health officials think the mutations occurred as the infection spread in his body.
“According to the preliminary findings of the local epidemiological investigation, the most plausible hypothesis about transmission is that it occurred through environmental exposure to areas where either sick or dead birds or sea mammals were found close to the residence of the case,” WHO officials said.
The Chilean case is the 11th in humans seen since January 2022, according to the CDC. The virus has at times spread among mammals, including at a Spanish mink farm last fall, and “continued sporadic human infections are anticipated,” the CDC said.