Tuesday April 18, 2023 | 9:29 a.m.
The Chilean Ministry of Health reported, at the end of March, the first human case of bird flu in the country. It was a 53-year-old man, a resident of the north of the trans-Andean country.
Now, the latest news once again has the Chilean patient as the protagonist after the Centers for Disease Control and Prevention (CDC) reported that an isolated sample of the man contains two genetic mutations that are signs of adaptation to mammals.
In experimental animal studies, the mutations, both in what is known as the PB2 gene, had previously been shown to help the virus replicate better in mammalian cells, agency officials reported.
And after clarifying that “the risk to the public remains low,” they stressed that the Chilean man remains hospitalized, and that no additional human cases have been associated with him.
In addition, the experts stressed that the sample was missing other critical genetic changes that scientists believe would be necessary for the H5N1 virus to spread efficiently among humans. Included among them are mutations that would stabilize the virus and help it bind more tightly to human cells.
“There are three main categories of changes that we think H5 has to undergo to go from being an avian virus to being a human virus,” explained Richard J. Webby, an avian flu expert at St. Jude Children’s Research Hospital. The sequences of the person in Chile have one of those kinds of changes. But we also know that of those three sets of changes, this is the easiest for the virus to do.”
The ones found are PB2 mutations, which have already been seen in other mammals infected with this version of the virus, as well as in some people infected with other versions of H5N1.
For the experts, it is most likely that the mutations arose in the Chilean patient during the course of his infection.
In the opinion of influenza virologist at Emory University, Anice C. Lowen, what happened “is a step on the road to adaptation to humans and an increased risk to humans.” “So it’s certainly concerning,” she added, though she acknowledged that “these mutations alone probably aren’t enough to produce a virus that spreads easily between humans.”
In a statement from the CDC’s National Center for Immunization and Respiratory Diseases, acting director of the influenza division, Vivien Dugan, noted that “these genetic changes have been seen previously with previous H5N1 infections and have not resulted in spread between people”.
“However, it is important to continue to closely observe each case of human infection, as well as other mammalian spread events, and follow the viral evolution in birds,” said Dugan, for whom “it is necessary to remain vigilant for changes that would make these viruses are more dangerous for people.”
The sample was sequenced by the National Influenza Center of Chile and uploaded into GISAID, an international database of viral genomes.
The Chilean Ministry of Health had reported the case to the World Health Organization (WHO) on March 29. The patient developed respiratory symptoms, including a cough and sore throat, and was hospitalized when his condition worsened.
And while it is still not clear to experts how the man became infected, the virus had recently been detected in birds and sea lions in the region where the patient lives.
“Based on preliminary findings from local epidemiological investigation, the most plausible hypothesis for 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,” the WHO reported. last week.
The Chilean man is the 11th reported human case of H5N1 since January 2022, according to the CDC, and none of them were associated with possible person-to-person 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.
However, the issue of human-to-human spread is a latent concern for health authorities. “The documented mutations in the Chilean patient are a step in the wrong direction,” Lowen admitted.
It is that, according to experts, the possibility that avian influenza, which is well adapted to birds, could evolve to spread more easily between humans could trigger another pandemic. This version of the virus has spread rapidly through wild birds in the Americas, causing regular outbreaks in farmed birds.
The virus has become so widespread in birds that it has repeatedly spread to mammals, and “continued sporadic human infections are anticipated,” the CDC wrote in a recent technical report.
What is bird flu?
Avian influenza or influenza is an infectious disease that mainly affects birds and is caused by a virus from the Orthomyxoviridae family.
Some avian influenza virus subtypes are highly pathogenic, mainly due to type A subtypes (H5 and H7). They can cause severe disease in birds and spread rapidly, with high mortality rates in different bird species, indicate from the WHO.
“Most circulating influenza viruses in birds are not zoonotic. However, some highly pathogenic avian influenza strains have the ability to infect humans, posing a threat to public health. The H5N1 virus, the same one that was detected in infected birds in Argentina, was responsible, in 1997, for a large outbreak in Hong Kong and China.
Wild birds, mainly migratory, are the natural host of the virus and are the main spreading factor throughout the American continent. Meanwhile, poultry populations can acquire the disease through contact with infected wild birds.
Since 2003, this avian influenza virus and others have spread from Asia to Europe and Africa. In the Americas, this virus was first identified in domestic and wild birds in December 2014, in the United States.
