The spillover of bird flu to mammals must be ‘monitored closely,’ WHO officials warn: ‘We need to be ready to face outbreaks in humans’

H5N1 avian flu has existed for a quarter century, WHO Director General Tedros Adhanom Ghebreyesus said at a news conference. But new reports that the disease has crossed into small mammals like minks, otters, foxes, and sea lions are cause for alarm, given the species’ similarities with humans.

While the risk to people remains low, according to Ghebreyesus, public health officials must prepare “to face outbreaks in humans,” Dr. Sylvie Briand, director of Global Infectious Hazard Preparedness and Emergency Preparedness at the WHO, said.

Since H5N1 was identified in 1996, only rarely have human cases occurred, and there has been no sustained transmission among humans, Ghebreyesus said. But he added: “We cannot assume that will remain the case. We must prepare for any change in the status quo.”

He cautioned people against touching or collecting sick or dead animals, and encouraged them to report the incidences to local authorities.

Countries must strengthen their avian flu surveillance in areas where humans and wild animals interact, Ghebreyesus insisted. And public health officials must work with manufacturers to ensure that vaccines and antivirals are available for global use, he added.

A growing mammalian outbreak

Tests on several sea lions and a dolphin found dead in Peru in November have returned positive for the concerning strain of bird flu, Peruvian veterinary authorities said Tuesday, the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota reported. At least 585 sea lions and 55,000 birds have been found dead in the country, their deaths likely due to H5N1, a federal agency reported Monday.

What’s more, a lion held in a Peruvian zoo recently died of the virus, CIDRAP recently reported, citing media reports crediting the country’s health ministry.

The cases join other recent, similar reports of bird flu outbreaks among small mammals, including at a mink farm in Spain. A “mass mortality event” among seals on Russia’s Caspian Sea coast in December was caused by avian flu, though the strain was not named, CIDRAP recently reported, citing the country’s Dagestan State University.

It’s trend that should concern humans, Mike Ryan, executive director of the WHO’s health emergencies program, said Wednesday.

“Small mammals may not look like us,” but they share many physical similarities with humans, he said. “That’s why drugs are tested on animals.”

Worst outbreak in U.S. history for birds

The H5N1 strain of avian flu has been responsible for the deaths of tens of millions of birds in the U.S. in recent months, and countless others worldwide. The strain—first identified in domestic waterfowl in China in 1996—is behind nearly 58 million U.S. bird deaths in the past year. These deaths have occurred both directly due to the virus and indirectly, when flocks are culled to curb further exposure, according to the U.S. Centers for Disease Control and Prevention. The virus has a near 100% fatality rate among birds, killing most infected within 48 hours.

This season’s bird flu outbreak is the worst in U.S. history, having surpassed a 2015 outbreak the CDC once called “arguably the most significant animal health event in U.S. history.” That year, nearly 51 million birds died nationally due to H5N1 and related avian flu viruses. This season’s outbreak is also the worst in U.K. history, with farmers in England ordered to keep their birds indoors as of Nov. 7 in a poultry “lock down” of sorts.

The so-called “R naught” value—or the number of people infected by a single infected person, on average—for COVID initially ranged from 1.5 to 7, and now sits upwards of 12. 

The R naught value of H5N1 among birds: “around 100,” Rajiv Chowdhury, senior epidemiologist and professor of global health at Florida International University, recently told Fortune.

Dangerous for people, too

Economic and food-supply issues aside, the strain has sickened people, too, albeit in small numbers so far. But the trend of minimal transmission among humans may not hold, experts warn. The WHO recently reported that a previously healthy Ecuadorian girl had been hospitalized with the virus. Just how she contracted the virus is uncertain and under investigation, but poultry her family had recently purchased died without apparent cause. 

The likelihood of human-to-human transmission of H5N1 is “very low,” Chowdhury said. But if it were to occur in a sustained manner, it could rock the globe in a way not seen since the 1918 Spanish Flu.

If H5N1 indeed makes a sustained crossover to humans, “the potential impact could be significant,” he says, signifying the start of a “new global influenza pandemic.”

This is a developing story and will be updated.

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