A sample of bird flu isolated from a Chilean man who fell ill last month contained two genetic mutations indicative of adaptation to mammals, officials from the Centers for Disease Control and Prevention said Friday. In experimental animal studies, the two mutations, both in what is known as the PB2 gene, have been shown to help the virus replicate better in mammalian cells.
Health officials said the risk to the public remains low, and no additional human cases have been linked to the Chilean man, who remains in hospital.
Moreover, the sample was lacking other critical genetic changes that scientists believe would be necessary for the virus, known as H5N1, to spread efficiently between humans, including 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 must undergo to switch from being an avian virus to a human virus,” said Richard J. Webby, an avian influenza expert at St. Jude Children’s Research Hospital. “The sequences taken from the person in Chile have one of those classes of changes. But we also know that of those three sets of changes, this is the easiest one for the virus to do.”
PB2 mutations have been found in other mammals infected with this type of virus, as well as in some people Infected with other versions of H5N1. Experts said the mutations likely appeared in the Chilean patient during the time he was infected.
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“So it’s definitely exciting to see them,” said Anice C.
She added that these mutations alone may not be sufficient to produce a virus that spreads easily between humans.
“These genetic changes have been seen before with previous H5N1 infections, and they did not result in human-to-people spread,” Vivian Duggan, acting director of the Division of Influenza at the CDC’s National Center for Immunization and Respiratory Diseases, said in a statement.
“However, it is important to continue to look carefully at each case of human infection, as well as other indirect events to mammals, and to track viral evolution in birds,” said Dr. Duggan. “We need to remain vigilant for changes that would make these viruses more dangerous to people.”
The sample was arranged by Chile’s National Influenza Center and uploaded to GISAID, an international database of viral genomes, overnight, according to CDC officials.
The Chilean Ministry of Health reported the case to the World Health Organization on 29 March. The patient, a 53-year-old man, developed respiratory symptoms, including cough and sore throat, and was hospitalized when his condition deteriorated, according to the Ministry of Health. from
The investigation into the case is still ongoing, and how the man was injured remains unclear. But the virus was recently discovered in birds and sea lions in the area where the man lives.
WHO stated that “According to the preliminary results of the local epidemiological investigation, the most plausible hypothesis about transmission is that it occurred through environmental exposure to areas where sick or dead birds or marine mammals were found near the place of residence of the case.” last week.
This is the 11th reported human case of H5N1 since January 2022, according to the CDC, and none has been linked to human-to-human transmission. Since the H5N1 virus was first detected in birds in 1996, hundreds of human infections have occurred globally, mostly in people who have been in close contact with birds.
However, experts have long worried about the possibility that avian influenza, which is well adapted to birds, could evolve to spread more easily between humans, potentially triggering another pandemic. An outbreak of H5N1 in a Spanish mink farm last fall suggests that the virus can adapt to spread more efficiently among at least some mammals. Each human infection gives the virus more opportunities to adapt.
Dr Lewin said the mutations documented in the Chilean patient are “a step in the wrong direction”.
This type of virus spread rapidly among wild birds in the Americas, resulting in regular outbreaks in farmed poultry. The virus has become so widespread in birds that it has frequently passed on to mammals, the CDC wrote in a recent technical report.