The H5N1 bird flu has spread to another Cambodian resident, WHO officials say, urging ‘heightened vigilance from all countries’

The WHO “urges heightened vigilance from all countries,” Dr. Sylvie Briand, director of Global Infectious Hazard Preparedness and Emergency Preparedness for the organization, said at a news conference. WHO officials were conferencing with Cambodian health officials, performing a risk assessment as she spoke.

H5N1 is “worrying, given the wide spread of the virus in birds around the world and increasing reports of cases in mammals, including humans,” she said. She characterized the virus as a “severe respiratory disease with a range of symptoms, from mild to fatal.”

The mortality rate is over 50%, she added.

The girl, from the southeastern province of Prey Veng, reportedly became ill Feb. 16, suffering from a 102-degree fever, cough, and throat pain, according to a tweet from the Cambodian government. She died shortly after arriving at a hospital in the capital, Phnom Penh, the Associated Press reported, citing the country’s health ministry.

The Khmer Times, a Cambodian news outlet, reported Thursday that 12 additional people from Prey Veng were being tested for H5N1, also citing the health ministry. Four of the 12 had begun to show symptoms, and results of lab testing should be released Friday, according to the Times.

It has not yet been determined how the girl or her dad were infected, though 22 chickens and three ducks at her home recently died, and there have been an unusual number of deaths among wild birds in the area as of late, BNO News reported Wednesday, citing Cambodian government officials. It’s also unclear if the girl’s contacts who are experiencing symptoms had contact with birds.

If human-to-human transmission of H5N1 is confirmed in Cambodia, interventions like isolating cases, contact identification, and the use of antivirals after exposure can be implemented, Briand said.

Increased spread among mammals, including humans

Recent days have brought increased reports of H5N1 bird flu spreading among mammals throughout the world—a situation that must be “monitored closely” owing to their physiological similarities with humans, WHO Director General Tedros Adhanom Ghebreyesus said at a Feb. 8 news conference.

H5N1 avian flu, rare in humans, is almost always transmitted by direct contact with sick birds. Roughly 900 human cases have been reported over the quarter century it’s been known to exist, with no sustained transmission reported among humans.

But “we cannot assume that will remain the case,” Ghebreyesus said Feb. 8. If birds have transmitted the virus to small mammals and it’s spreading among them—as seems to be the case, given recent mass mortality events among minks and other small mammals—it could signal that the virus has evolved and could spread more easily among humans.

“Clusters” of human H5N1 cases have occurred since 1997, “so the question is whether this cluster is due to common exposure to chicken or birds, or sustained human-to-human transmission,” Dr. Jay Varma, chief medical adviser at the New York-based think tank Kroll Institute, told Fortune.

“The latter would be worrisome.”

This is a developing story and will be updated.

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