Bird flu found in dolphins in Florida and guinea pigs in Sweden

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A dolphin swims alongside a boat in the Ten Thousand Islands off Everglades City, Fla., December 2019. (Erik Freeland/The New York Times)

A dolphin swims alongside a boat in the Ten Thousand Islands off Everglades City, Fla., December 2019. (Erik Freeland/The New York Times)

A bottlenose dolphin found dead in a Florida canal last spring tested positive for a highly virulent strain of bird flu, scientists said Wednesday. The announcement came a week after Swedish officials reported finding the same type of bird flu in a stranded guinea pig.

This version of the virus, which has spread widely among North American and European birds, has affected an unusually wide range of species. But these findings represent the first two documented cases in cetaceans, a group of marine mammals that includes dolphins, porpoises and whales.

It’s too early to say how frequently the virus infects whales, but its discovery in two different species on two different continents suggests there have “almost certainly” been other cases, said Richard Webby, an influenza virologist at St. Jude Children’s Research Hospital in Memphis, Tennessee.

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“Our surveillance activities globally are never sensitive enough to pick up the only two events of this kind,” said Webby, who was not involved in the initial detection of the virus but is now working with the Florida team on follow-up studies.

The virus has become so widespread in birds that it would not be surprising to see the pathogen show up in other unexpected species, he added. “Unfortunately, I think this might just be a sign of things to come if this virus doesn’t go away,” he added.

Experts emphasize that the risk to humans remains low. In the United States, the version of the virus circulating has caused only one documented human infection in a person known to have had contact with poultry, according to the Centers for Disease Control and Prevention.

But the spread of the virus to new species poses potential risks to wildlife and gives the virus new opportunities to mutate and adapt to mammalian hosts.

This strain of bird flu, known as Eurasian H5N1, has spread rapidly through domestic poultry, affecting tens of thousands of farmed birds, according to the Department of Agriculture. Compared to previous versions of the virus, this lineage has taken a particularly heavy toll on wild bird populations, bald eagles, owls, pelicans and more.

This, in turn, has endangered mammals that encounter wild birds. As the outbreaks grew in the spring, the virus appeared in foxes, bobcats, skunks and other species. The virus has also been blamed for an increase in seal strandings in Maine, where bird flu has been detected in both gray and spotted seals.

The Florida dolphin, a juvenile male, was found in March in a canal in Dixie County, where area residents noticed the animal had been caught between pier pilings and a seawall, Dr. Michael Walsh, a veterinarian at the University of Florida College of Veterinary Medicine who directs the university’s marine animal rescue program.

When rescuers arrived, the dolphin was dead, he said. The team, which routinely performs autopsies, collected a number of samples from the dolphin and stored them until they could be analyzed in more detail.

At the time, the researchers had no reason to suspect that bird flu had made its way to dolphins, and they were in no particular rush, said Walsh, who collaborated on the study with Dr. Robert Ossiboff, a veterinary pathologist, and Andrew Allison, a veterinary virologist, both at the University of Florida College of Veterinary Medicine.

When the results came back this summer, they revealed signs of inflammation in the dolphin’s brain and surrounding tissue, Walsh said. Researchers have previously documented encephalitis in fox kits infected with the virus, which can cause neurological symptoms in birds and mammals.

Subsequent laboratory tests showed Eurasian H5N1 in the dolphin’s brain and lungs. “The brain tissue showed a really high level of virus,” Walsh said.

Whether the virus contributed to the dolphin’s death is still unknown, as is exactly how the animal contracted it. But it’s not hard to imagine a young dolphin investigating an ailing bird near the shoreline, Walsh said, adding: “These animals are always curious about their environment and checking things out. So if he came across one sick, either dying or dead, bird, he might be very curious about it. He may be talking about it.”

The virus was also responsible for the death of a guinea pig found stranded in Sweden in June, the Swedish National Veterinary Institute said last week. According to the agency, the pathogen was found in several of the animal’s organs, including the brain.

So far, there is no evidence that whales are spreading the virus to each other, Webby said. And Webby’s team, which has isolated and sequenced the virus detected in the Florida dolphin, has found no evidence that it has developed mutations associated with adaptation to mammals. “It still looks a lot like a virus that you would pick up from a bird,” he said.

But now that dolphins and porpoises are known to be susceptible, researchers can start looking for the virus more proactively, including in any tissue samples they’ve previously collected.

“Now everyone is going to be on the lookout for this,” Walsh said. “And that will help tell us how serious this really is for whales on the coasts.”

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