The USA reports the first serious case of bird flu in humans

There have been 61 human cases of bird flu reported in the United States this year. To date, no human-to-human transmission has been documented. Most cases were mild and were found in farm workers who were exposed to the virus through interactions with infected poultry or cattle. Common symptoms in previous cases included conjunctivitis, coughing and sneezing.

Dr. Peter Chin-Hong, a professor of medicine at the University of California, San Francisco, who studies infectious diseases, said the Louisiana case highlights the risks of off-farm exposure.

“We have focused on dairy workers and poultry workers, but dealing with dead birds in your backyard poses an increasing risk,” he said.

Daskalakis said the CDC is still working to better characterize the virus’s genome, which will help researchers understand whether it has developed worrisome mutations that could allow it to spread from person to person.

Early indicators in the Louisiana case suggest that the version of the virus causing the infection is similar to that circulating in wild birds and poultry in British Columbia, Canada and Washington state.

A teenager in British Columbia was hospitalized in November after contracting the same genotype of bird flu virus. Canadian health authorities have not been able to determine the source of the teenager’s infection.

“This shows that bird flu can make people very sick, and to me that’s linked to the case in British Columbia,” Chin-Hong said. “These patients both have the same variant.”

The CDC said the development does not change its assessment of the immediate public health risk of H5N1, which it said remains “low.”

H5N1 began circulating widely among wild birds in the United States in 2022 and then spread to poultry farms and backyard flocks. At least 123 million birds have been killed or euthanized because of the virus since 2022, according to the CDC.

This spring, bird flu began spreading among dairy cows, and since then the virus has been detected in cows in at least 16 states.

Studies on dairy farms have shown that the virus can spread efficiently between mammals. Scientists have found that it likely spreads from livestock to other livestock through raw milk because infected cows shed large amounts of the virus through their mammary glands.

Although there is no evidence that the virus spreads between people, scientists fear it could mutate and develop this ability, which could trigger the next pandemic.

There have been two cases in the U.S. to date in which health authorities have been unable to determine the source of a person’s exposure to bird flu. One of those was an infection reported in November in a California child. The other case involved a hospital patient in Missouri who tested positive for H5N1 in August and recovered.

Daskalakis said the CDC considers the Louisiana case to be the first serious H5N1 infection because other medical conditions were likely the cause of the Missouri patient’s hospitalization.