Since its arrival in South America in 2022, the highly contagious H5N1 bird flu strain has exhibited unprecedented spread among both wild birds and marine mammals. This heightened transmission poses an increased risk of evolving into a more substantial threat to human populations. Influenza researcher talk about the virus and how it fits into a pattern scientists have long been warning of, as climate change throws ecosystems out of whack, enabling disease to thrive.
The latest H5N1 outbreak has killed millions of birds, driving up egg prices and causing farmers to lose or kill 58 million chickens. It has also spread to wild animals, causing an uptick in infections among mink—a development that has experts worried.
That’s because this particular strain of H5N1 has the potential to jump from species to species, something called “enzootic” transmission. Once a virus becomes enzootic in a particular species, it can persist for decades—devasting wildlife populations and poultry farms. The new outbreak is also different because it has affected a more comprehensive range of species than earlier ones, including mammals like mink and sea lions.
Those animals are particularly vulnerable to the virus because they live and breed in close contact with each other, often sharing food sources and rafts of water. In the case of sea lions, that has meant thousands have died in Peru and Chile. A new study shows that the same genetic mutations that enabled H7N9 to mutate and spread from poultry to humans are present in the South American strains. That’s why researchers are calling for closer surveillance and research.
Hensley says a big concern is that the virus is spreading to marine mammals, which can’t be protected by vaccines for avian flu, and could then re-infect human populations, potentially triggering a pandemic. But he emphasizes that the risk to people right now is still low. The CDC has been following the situation closely and taking routine preparedness and prevention measures, including urging people who work with birds to take precautions.
The other primary concern is that this virus affects more types of birds and marine mammals than previous strains, thus making it more likely to cross species barriers into those populations. The wide range of hosts also increases the likelihood of the virus mutating to create more dangerous versions. That’s why scientists everywhere are racing to track the virus’s evolution in the wild, with some of that work being done on the beaches of Argentina’s Peninsula Valdes. Each year, the beach teems with elephant seals raising their pups near one another. But this year, many of those pups died, with some dying as soon as they were born. The same genetic mutations appear in those carcasses. Scientists are hoping to understand why. By tracking those genomes, they may identify the fundamental changes that allow a virus to survive in new host species and spread more aggressively.
