Bird Flu Samples From Very Ill Patient Had ‘Concerning’ Mutations

Tiny genetic alterations could help the bird flu virus enter cells in the upper respiratory tract, the C.D.C. said. But there is no sign that mutations are widespread in nature.

After someone in southwest Louisiana was hospitalized with a severe case of bird flu, the first such illness reported in the United States, health workers swabbed the person’s nose and throat, looking for genetic clues about the virus.

On Thursday, federal health officials reported some unsettling results. Some of the genetic samples contained mutations that in theory might help the bird flu virus, H5N1, infect people more easily.

One of those mutations was reported last month in a viral sample taken from a teenager with a severe case of bird flu in British Columbia, Canada. The teenager was placed on a ventilator during a long hospitalization.

Worrying as those severe cases are, the new report about the Louisiana patient contained some reassuring findings, scientists said.

For one thing, the mutations seemed to develop as the virus adapted to its human host. The genetic changes were not present in H5N1 samples from a backyard poultry flock that infected the patient, the Centers for Disease Control and Prevention said.

That suggested that viruses in nature had not yet acquired the concerning mutations. Still, every additional human case gives H5N1 more opportunities to adapt to people, potentially making it more capable of spreading from one person to the next.

That poses an even greater risk as the flu season continues. In someone infected with both H5N1 and the seasonal flu, the viruses might swap genes, potentially making the bird flu capable of spreading between people as efficiently as the seasonal flu does.

“If there are all these people getting infected, that provides so many opportunities for the virus to better adapt,” Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada, said of bird flu.

“It has the potential to really harm a lot of people,” she said.

Scores of people in the United States have contracted bird flu this year, most of them from infected cows or poultry. The virus cannot yet spread easily among people, and pasteurized dairy products remain safe to consume.

But the outbreak in dairy cattle and poultry has prompted a state of emergency in California and an increase in egg prices nationwide.

Agriculture officials in Oregon this week reported that a house cat contracted bird flu and died after eating frozen raw-turkey chow that was contaminated with the virus.

Northwest Naturals, the raw pet-food company that made the infected chow, said on Tuesday that it was recalling a batch of its feline turkey recipe that had tested positive for the virus.

It is not clear how the patient in Louisiana is faring. A spokeswoman for the Louisiana Department of Health declined on Friday to answer questions about the person’s condition. It is also not clear when in the course of the patient’s hospitalization the swabs were taken.

The mutations observed in the patient could help the virus more easily infect cells in the upper respiratory tract, C.D.C. investigators concluded. But the mutations were found in the later stages of the infection and did not occur frequently in the genetic samples.

C.D.C. scientists described the mutations as “concerning” in the update posted to the agency’s website. But, they added, “these changes would be more concerning if found in animal hosts or in early stages of infection (e.g., within a few days of symptom onset) when these changes might be more likely to facilitate spread to close contacts.”

The C.D.C. said it had found no evidence that the virus had spread from the patient in Louisiana to other people. And the mutations found in the samples may not be enough on their own to enable the virus to spread among people.

H5N1 needs to be able not only to bind to and enter human cells, Dr. Rasmussen said, but also to replicate and shed new viruses once inside.

Federal health officials said that the viruses from the Louisiana patient were closely related to so-called candidate viruses that manufacturers already have available for making bird flu vaccine.

Dr. Rasmussen questioned why those vaccines were not yet being offered to groups of people, like farmworkers, at the greatest risk of contracting infections that could set the stage for the virus to mutate.

“The one way I think would be pretty effective at reducing the number of human infections would be vaccinating people at high exposure risk,” she said.

Referring to the finding that the candidate vaccine viruses are likely to be effective, Dr. Rasmussen said, “What good is that information if we don’t have a plan for how to use it?”