Although a man in Chile has been infected with a bird flu that has concerning mutations, the threat to humans remains low, according to U.S. health officials.
Authorities said Friday that past animal studies suggest mutations could cause the virus to be more harmful or spread more easily, but that there is no evidence the mutations would make it easier for the virus to take root in a person's upper lungs.
The Centers for Disease Control and Prevention's Vivien Dugen said the mutations do not alter the assessment of the overall risk to people from H5N1, which "continues to be low."
The agency's officials said the mutations may have occurred after the man was sickened.
New lab analysis examined the virus in the lungs of a 53-year-old man in the country's Antofagasta region.
A World Health Organization summary of the case said he may have become infected through contact with sick or dead birds, or infected sea lions.
The man had been healthy and had not traveled recently, but he started getting a cough, a sore throat and hoarseness on March 13. His symptoms worsened, and he was sent to an intensive care unit and treated with antiviral medicines and antibiotics.
The Centers for Disease Control and Prevention said the patient is still hospitalized and being monitored.
Genetic sequencing this week revealed the two concerning mutations and Chilean and American health officials have been working together on the investigation.
The case was the second human H5N1 bird flu virus infection reported in South America and the 11th globally since January 2022.
In the U.S., one H5N1 case was reported last year in a person who reported fatigue without any other symptoms after poultry-culling activities.
The mutations have appeared only in one hospitalized patient, and there is no evidence that the mutated virus has spread to others, mixed with other flu viruses or developed the ability to fight off current medicines or evade vaccines, they added.
"Nevertheless, it’s important to continue to look carefully at every instance of human infection," Dugan said. "We need to remain vigilant for changes that would make these viruses more dangerous to people."
Such changes have been witnessed in past bird flu infections.
More than 450 people have died in the past two decades from bird flu infections, according to the World Health Organization.
The majority of humans who have been infected have gotten it directly from birds.
In the U.S., bird flu has recently been found in wild birds in every state, in addition to in commercial poultry operations and backyard flocks.
Since the beginning of last year, tens of millions of chickens have died of the virus or have been killed to stop outbreaks from spreading, leading to soaring U.S. egg prices.
Recently, several California condors have been reported dead, and a beloved peregrine falcon was also killed by the disease.
As bird flu hits other species, scientists fear that the virus – which has been spreading to birds and animals around the world – could evolve to spread more easily among people.
The National Health Commission of the People’s Republic of China reported a confirmed case of human infection with H3N8 bird flu on March 27. The adult patient from Guangdong Province had multiple underlying medical conditions and was hospitalized with severe pneumonia 13 days before his death on March 16 – the first fatality from that virus ever reported, and the third human infection.
The Associated Press contributed to this report.