US alert as H5N1 bird flu reported in person exposed to infected cattle

An individual in Texas has caught bird flu from a cow, raising concerns that the highly pathogenic H5N1 is becoming fitter.

In a health alert on Monday, Texan health officials said a dairy worker had developed mild conjunctivitis, or ‘pink eye’, after close contact with a dairy herd. Testing later confirmed that they had caught H5N1, in only the second human case in America.

The case adds a “notable” new dimension to an unprecedented outbreak that has already lapped the globe, raising questions about whether the virus is evolving to better infect mammals and people.

“[The] infection in someone with exposure to sick animals is not surprising, but [is] concerning,” said Dr Jennifer Nuzzo, director of the Pandemic Center at Brown University School of Public Health in the US.

Writing on X (formerly Twitter), she added that the case is “notable” as the expanding “geographic and species spread increases concerns about virus’ future potential to infect humans”.

In recent years, H5N1 has killed millions of wild birds and poultry across the globe. But in a string of unexpected developments, it has also jumped to animals including cats, bears, foxes, mink and sea lions. This has raised concerns that the virus could have space to evolve to better infect and spread between mammals - and potentially also humans.

Cows were added to that ever-growing list just last week, when the United States reported H5N1 infections in dairy herds. Since then, cases have been confirmed or are under investigation in five states - Texas, Kansas, Michigan, New Mexico and Idaho.

Although cows can contract other forms of influenza and a study in 2008 found cattle could contract H5N1, this is the first time the virus has actually been found in herds.

While the cows do not become seriously ill, a race is now underway to determine whether they were infected via wild birds - which have been found dead on some farms - or whether the virus has started to spread between herds, which has not yet been proven nor ruled out.

It would be a concern if the virus has mutated to spread more easily between cows.

Scientists are also trying to determine how widespread the virus is in cattle, with calls for heightened surveillance in the US and beyond to better understand the situation.

“We should really test cows in Europe as well to understand how widespread such infections are,” said Prof Isabella Eckerle, co-Head of the Centre for Emerging Viral Diseases in Geneva. “[This] does not mean it will cause an outbreak… but having infected cows increases the risk due to closer human-animal contact (vs wildlife).”

On Monday, the Texas Department of State Health Services said the person infected is being treated with the influenza antiviral drug oseltamivir, which is sold as Tamiflu, and their case appears mild. They are currently isolating, and health officials stressed that “the case does not change the risk for the general public, which remains low”.

“We are not aware of reports that any of this individual’s close contacts have developed any symptoms,” Nirav Shah, principal deputy director of the US Centers for Disease Control and Prevention (CDC), told STAT News. “The fact that there are not other samples cooking right now is reassuring… [but] We are still out there looking, to be very clear. Our antennae are up.”

Prof Sam Scarpino, a professor of the Practice in Health Sciences and Computer Science at Northeastern University, added that the list of symptoms is reassuring. Conjunctivitis is a common symptom of bird flu in people, because our eyes actually contain “bird-flu-friendly” receptor cells.

“Reports from Texas suggest the individual had direct contact [with] infected cows and has minimal symptoms aside from eye inflammation. This is great for the patient, ie no pneumonia, and suggests the virus isn’t readily able to move from person-to-person,” he said on X.

Prof Scarpino added that he would be more concerned if this case had come via a pig, which are known to be “evolutionary laboratories” for flu, because they contain both avian and human cell receptor types in their airways and lungs - raising the prospect for viruses to merge into something new.

Avian flu is known to occasionally jump to people, but usually via birds directly. Three cases have been reported in Cambodia so far this year, and a 21-year-old student died last week in Vietnam. In total, almost 900 people have caught the virus in 23 countries since it was first detected in 1997, with just over half of these cases fatal.

Although outbreaks in flocks of poultry result in culling on a huge scale in an attempt to minimise the spread, it looks like this will not take place for cattle. The CDC has so far told the farmers with implicated herds to destroy the milk produced by infected cattle, though it is thought that the pasteurisation process could also kill the virus.

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