Updated May 4, 2024 - Science

Bird flu's wild range

A map of the United States shows counties where avian flu has been detected in wild mammals. The disease is widespread, particularly across New England, the upper midwest, Colorado and the Pacific northwest. It's been prevalent in red foxes but has also been found in a dolphin in Florida and a polar bear in Alaska.
Data: USDA; Map: Danielle Alberti/Axios

A polar bear in the Arctic, red foxes in Europe, penguins in Antarctica and a wide range of other wild animals have been infected with the flu virus strain currently spreading in dairy cattle in the U.S.

Why it matters: Up to 75% of new and emerging infectious diseases in people come from animals, and most of those can be traced back to wildlife. Monitoring wild animals for diseases can help scientists identify emerging health threats.

  • Government agencies in the U.S. and around the world monitor wild birds for avian influenza, which spreads in bird populations without causing symptoms, and select animals for other pathogens.
  • But on the whole, there is "very little surveillance of wildlife for any diseases," says Thomas Gillespie, a disease ecologist at Emory University. An exception is animals that are commercially important — like deer that people pay to hunt.

Catch up quick: Outbreaks of avian flu in farmed poultry and wild birds started to increase around the world in 2020.

  • Soon after, the virus started to kill mammals — seals from Chile to Russia to Maine, red foxes in Europe and the U.S,. sea lions in Peru and other species.
  • Bird flu has affected nearly 20 wild mammal species in the U.S. since 2022, including brown bears, skunks, mountain lions and a bottlenose dolphin in Florida.

Now cows are being infected. (They become ill but recover with treatment).

  • There's been one mild human infection detected so far, in a person exposed to dairy cattle, but some researchers suspect not all cases in workers are being spotted.
  • A report published Friday suggests that may be "the first detected case of the H5N1 virus transmitting from a mammal to a person," STAT's Helen Branswell reported.
  • The CDC has said the risk to the general public is low.

The intrigue: "We’ve been seeing bird-to-mammal transmission events in a diversity of wild and domestic animals for about the last 4-5 years," Gillespie says.

  • Scientists are watching for evidence of the virus being transmitted from one mammal to another, which increases the risk of the virus for humans.
  • The USDA has confirmed this version of influenza is being transmitted between different cows in the same herd — and between herds when they are moved — but exactly how is still an open question.
  • There is also some evidence the virus was transmitted from mammal-to-mammal in farmed minks.

Wild animals are in general thought to get the virus by eating an infected bird or being exposed to its feces.

  • But, "with wildlife it is really hard to know if mammal-to-mammal spread or individual events" because there is little surveillance, Gillespie says.
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