FRIDAY, Nov. 22, 2024 (HealthDay News) -- In a development that health experts have warned might come, Canadian officials report that the bird flu virus isolated from a sick teen in Vancouver shows mutations that could help it spread more easily among humans.

At this point, there is no evidence that this particular mutated H5N1 virus has traveled beyond the one Canadian patient: After monitoring of dozens of potential contacts among the teen’s friends, family and health care providers, “no further cases have been identified,” Dr. Bonnie Henry, provincial health officer for the province of British Columbia, told CNN.

Still, scientists say the genetic changes seen in the Canadian case are ominous.

“Certainly, this is one of the first times that we’ve really seen evidence of these sort of adaptation mutations in H5,” Dr. Jesse Bloom, a computational virologist at the Fred Hutchinson Cancer Center in Seattle, told CNN.

Bloom noted that the teen started experiencing symptoms a week before being admitted to the hospital, and that may have given the virus time to become better at entering the cells it was trying to infect.

Importantly, the virus that infected the teen, who remains in critical but stable condition, is not the same strain as the one striking dairy cattle in the United States. Instead, it more closely resembles an H5N1 strain that is circulating in wild bird flocks in the Pacific Northwest, CNN reported.

Canadian officials say they still don’t know how the teen was infected, since there was no known contact with wild birds.

The three mutations seen in the Canadian case sit at spots on the genome that scientists have deduced would allow it to attach more easily to human cells, CNN reported.

“It’s caught the attention of a lot of flu virologists, including myself, because some of the sequence has evidence of some of the types of mutations we worry about,” Bloom said.

Meanwhile, a child in California tested positive for bird flu earlier this week, despite having no known contact with infected animals.

"California has identified a possible bird flu case in a child in Alameda County who was tested for mild upper respiratory symptoms. The child, who has been treated, is recovering at home," the California Department of Public Health (CDPH) said in a news release.

While the patient had no known contact with an infected animal, health officials are investigating a possible exposure to wild birds, the CDPH added.

Importantly, "the positive test showed a low-level detection of the virus, indicating the child was not likely infectious to others," they noted. "Repeat bird flu testing on the child four days later was negative, and additional testing shows the child was also positive for respiratory viruses that could be the cause of their cold and flu symptoms. The test specimens are being sent to CDC [U.S. Centers for Disease Control and Prevention] for confirmatory testing."

Even as the case was reported, California officials stressed the public health risk remained low.

“It's natural for people to be concerned, and we want to reinforce for parents, caregivers and families that based on the information and data we have, we don't think the child was infectious -- and no human-to-human spread of bird flu has been documented in any country for more than 15 years," said CDPH Director Dr. Tomás Aragón.

So far this year, 53 people have been confirmed to have bird flu in the United States, according to the CDC; all but one had been exposed to infected poultry or dairy cows.

In the California case, no person-to-person spread of the virus has been detected and the child's family members all tested negative.

Bird flu has been spreading in poultry since 2022, and cases in dairy cows began to crop up in March. The virus was discovered in a pig for the first time last month.

Bird flu infections in people -- nearly all among farmworkers -- have now been confirmed in seven states, with Oregon reporting its first human case last week.

California accounts for the largest share of human bird flu cases in the country, with 27 confirmed infections, not counting the child in Alameda County. Washington has recorded 11 cases, and Colorado 10, CDC data shows.

The latest cases fuel growing concern among public health experts that the ongoing bird flu outbreak will eventually trigger human-to-human transmission of the virus.

Across the country, more than 612 dairy herds in 15 states have been infected since the outbreak in dairy cows was first confirmed in March. Avian influenza has been spreading in wild and domestic birds in the United States for several years.

“We should be very concerned at this point,” Dr. James Lawler, co-director of the University of Nebraska’s Global Center for Health Security, told the New York Times recently. “Nobody should be hitting the panic button yet, but we should really be devoting a lot of resources into figuring out what’s going on.”

More information

The CDC has more on bird flu.

SOURCES: California Department of Public Health, news releaase, Nov. 19, 2024; British Columbia Ministry of Health, news release, Nov. 9, 2024; U.S. Centers for Disease Control and Prevention, news releases, Oct. 30, 2024; Oct. 24, 2024, Oct. 18, 2024; Oct. 3, 2024; New York Times

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