Avian flu shows signs of adapting to mammals – 04/21/2023 – Health

A sample of avian flu isolated from a Chilean man who fell ill last month contains two genetic mutations that are signs of adaptation to mammals, officials from the United States Centers for Disease Control and Prevention (CDC) said on the last day 14.

In experimental animal studies, mutations, both in what is known as the PB2 gene, have already 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, who remains hospitalized.

What’s more, the sample was missing other critical genetic changes that scientists believe are necessary 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.

“There are three broad categories of changes that we think H5 must undergo to go from being an avian virus to being a human virus,” said Richard Webby, an avian flu specialist at St. Jude. “The sequences from the Chile patient have one of these types 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 in some people infected with other versions of H5N1. The mutations likely arose in the Chilean patient over the course of his infection, experts said.

“We understand that they are a step on the path to adapting to humans and increase the risk for humans,” said Anice Lowen, an influenza virologist at Emory University. “So certainly it’s concerning to find them.”

But those mutations alone are probably not enough to produce a virus that spreads easily between humans, she added.

“These genetic changes have been seen in previous H5N1 infections and have not resulted in person-to-person transmission,” Vivien Dugan, acting director of the influenza division at the CDC’s National Center for Immunization and Respiratory Diseases, said in a statement.

“However, it is important to continue to carefully observe all cases of human infection, as well as other spread events in mammals, and to follow viral evolution in birds,” said Dugan. “We need to be aware of changes that would make these viruses more dangerous for people.”

The sample was sequenced by Chile’s Centro Nacional de Influenza and uploaded to Gisaid, the international database of viral genomes, CDC officials said.

The Chilean Ministry of Health reported the case to the WHO (World Health Organization) on March 29. The 53-year-old patient developed respiratory symptoms, including a cough and sore throat, and was hospitalized when his condition deteriorated, according to the charity.

The investigation into the case continues, and it remains unclear how the man was infected. But the virus had recently been detected in birds and sea lions in the region where it lives.

“According to the preliminary results of the local epidemiological investigation, the most plausible hypothesis about the transmission is that it occurred through environmental exposure to areas where sick or dead birds or marine mammals were found near the case’s residence,” the WHO said in the week. late.

It is the 11th reported human case of H5N1 since January 2022, according to the CDC, none of which have been linked to 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 have been in close contact with birds.

Still, experts have long worried that avian flu, which is well adapted to birds, could evolve to spread more easily among humans, potentially triggering another pandemic. An H5N1 outbreak 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 documented mutations 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, causing regular outbreaks in 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.

^{Translated by Luiz Roberto M. Gonçalves}