by A bird flu sample isolated from a Chilean man who fell ill last month contains two genetic mutations that are signs of mammalian adaptation, officials at the Centers for Disease Control and Prevention said Friday. In experimental animal studies, mutations, both in what’s known as the PB2 gene, have previously been shown to help the virus replicate better in mammalian cells.
The risk to the public remains low, health officials said, and no other human cases have been linked to the Chilean man, who remains hospitalized.
In addition, the sample was missing other critical genetic changes that scientists believe would be required for the virus, known as H5N1, to spread efficiently among humans, including mutations that would stabilize the virus and help it bind more tightly to human cells. .
Sign up for the New York Times The Morning newsletter
“There are three main categories of changes that we think H5 must undergo to go from being a bird virus to being a human virus,” said Richard Webby, an avian flu expert at St. Jude Children’s Research Hospital. “The sequences of the person in Chile have one of those classes of changes. But we also know that of these three sets of changes, this is the easiest for the virus to make.”
PB2 mutations have been found in other mammals infected with this version of the virus, as well as some people infected with other versions of H5N1. The mutations most likely emerged in the Chilean patient over the course of his infection, experts said.
“We believe they are a step toward human adaptation and an increased risk to humans,” said Anice Lowen, an influenza virologist at Emory University. “So, certainly, it’s troubling to see them.”
But these mutations alone probably aren’t enough to produce a virus that spreads easily among humans, he added.
“These genetic changes have been seen before with previous H5N1 infections and have not resulted in spread among people,” said Vivien Dugan, acting director of the influenza division at the CDC’s National Center for Immunization and Respiratory Diseases. .
“However, it is important to continue to carefully scrutinize each case of human infection, as well as other spillover events in mammals, and monitor viral evolution in birds,” Dugan said. “We need to remain vigilant for changes that would make these viruses more dangerous to people.”
The sample was sequenced by the National Influenza Center in Chile and uploaded to GISAID, an international database of viral genomes, overnight, CDC officials said.
On 29 March, the Chilean Ministry of Health reported the case to the World Health Organization. The patient, a 53-year-old man, developed respiratory symptoms, including cough and sore throat, and was hospitalized as his condition worsened, according to the CHI.
The investigation into the case continues and it is not clear how the man got infected. But the virus had recently been detected in birds and sea lions in the region where humans live.
“According to the preliminary results of the local epidemiological survey, the most plausible hypothesis for the transmission is that it occurred through environmental exposure to areas where sick or dead birds or marine mammals were found near the residence of the case,” he said. the WHO last week.
It is the 11th reported human case of H5N1 since January 2022, according to the CDC, none of which have been associated with human-to-human transmission. Since H5N1 was first detected in birds in 1996, there have been hundreds of human infections worldwide, mostly in people who were in close contact with birds.
However, experts have long been concerned about the possibility that avian flu, which is well adapted to birds, could evolve to spread more easily among humans, potentially sparking another pandemic. An outbreak of H5N1 at a Spanish mink farm last fall suggests the virus is able to adapt to spread more efficiently among at least some mammals. And every human infection gives the virus more opportunities to adapt.
The mutations documented in the Chilean patient are a “step in the wrong direction,” Lowen said.
This version of the virus spread rapidly through wild birds in the Americas, resulting in regular outbreaks in farmed poultry. The virus has become so widespread in birds that it has repeatedly spread to mammals and “continued sporadic human infections are expected,” the CDC wrote in a recent technical report.
c.2023 The New York Times Society
