H5N1 bird flu samples taken from a seriously ill patient in Louisiana show signs of mutations that could make the virus more easily transmitted to humans, the Centers for Disease Control and Prevention (CDC) reported Thursday.
The patient, who has not been identified, is believed to have been hospitalized with severe respiratory symptoms and contracted bird flu from exposure to sick and dead birds from a backyard flock.
Apparently, the infected person is over 65 years old and has underlying health problems, and is the second patient hospitalized with the virus in the United States. That person was infected with a strain of the virus different from the one that affects dairy cows and is causing fear among the country’s agricultural workers.
Genetic analysis of two samples collected from the Louisiana patient suggests that the virus may have the ability to adhere to cells in the upper respiratory tract of humans.
This is worrying, experts say, because bird flu viruses like H5N1 typically attach to cell receptors found in birds and other animals, but not in humans. That’s why bird flu doesn’t usually infect humans or spread from person to person.
According to the CDC, one of the mutations was also seen in a sample from a British Columbia teenager hospitalized with bird flu.
Although the findings show that the virus has the capacity to mutate so that it could be more transmissible to humans, experts stopped short of suggesting that we are on the brink of a pandemic.
“There is no evidence that this person has infected others, and that is good,” said William Schaffner, an infectious disease expert at Vanderbilt University Medical Center. “It clearly means that we have to keep our attention on this and, in any case, intensify it even more.”
Paul Offit, a vaccine and infectious disease expert at Children’s Hospital of Philadelphia, said there is no evidence that the mutations were “functional,” meaning that the virus could actually attach to the upper respiratory tract and replicate and spread to other people. .
“I think that if there was clear and definitive evidence that the virus has mutated to the point that it can bind to the binding receptors in the upper respiratory tract, that is, the lining of the nose, the lining of the throat, the lining of the throat, the from the trachea and therefore reproducing in the upper respiratory tract, that would be concerning,” Offit said. “But the report doesn’t say that.”
In the report, the CDC stated that the detection “underscores the importance of continued genomic surveillance in people and animals, containment of avian influenza A(H5) outbreaks in dairy cattle and poultry, and prevention measures among people with exposure to infected animals or environments.”
The agency said the risk to the general public has not changed and remains low.
According to the CDC, 65 confirmed human cases of H5N1 had been reported in the United States as of Friday, most from exposure to infected poultry or dairy cows.
However, this figure is likely an understatement, as a CDC report released in November found evidence of asymptomatic bird flu infections in farm workers. There are no signs of contagion between people in any of the cases.
The Louisiana patient was infected with a strain called D1.1, closely related to other viruses recently detected in wild and poultry birds in the United States and in recent human cases in British Columbia, Canada, and Washington state.
The CDC said its analysis found no changes associated with markers that would mean antivirals, such as Tamflu, would not work against the virus. That is one of the agency’s criteria for deploying a bird flu vaccine.
Angela Rasmussen, a virologist specializing in emerging infectious diseases, noted on the social network X that the mutations identified in the patient were not present in bird samples, indicating that the changes developed in the patient after infection and are not circulating in the wild fauna.
He said it is “good news” because it “reduces the risk of transmission to another person and suggests that ‘human-adapted’ viruses are not emerging in birds.”
However, “the H5N1 situation remains grim” because human cases continue to increase, Rasmussen posted.
“We don’t know what combination of mutations would give rise to a pandemic-level H5N1 virus, and we can’t predict much from this sequence data,” he said. “But the more humans that become infected, the more likely it is that a pandemic virus will emerge.”
