Bird flu's wild range

Bird flu's wild range

Alison Snyder

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.
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Bird flu's big question: What's driving its spread

The bird flu outbreak in dairy cattle that's swept across nine U.S. states is posing perplexing questions about how the virus is spreading between animals and the risk posed to humans.

Why it matters: Detecting viral spread early and limiting how long the flu circulates in a population of animals cuts the odds it will mutate and adapt to other species.

• The fact that the virus has infected a range of animals and is already in more than 30 herds — and the resulting potential for contact with humans and other animals — has public health experts' radar up.

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