A bottlenose dolphin found dead in a Florida canal last spring has tested positive for a highly virulent strain of bird flu, scientists said Wednesday. The announcement came a week after authorities in Sweden announced they had found the same type of bird flu in a stranded porpoise.
This version of the virus, which has spread widely among birds in North America and Europe, 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 tell how often the virus infects cetaceans, but its discovery in two different species on two different continents suggests there have been “almost certainly” other cases, said Richard Webby, a virologist at the flu at St. Jude Children’s Research Hospital. in Memphis, Tennessee.
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“Our global surveillance activities are never sensitive enough to detect just two such events,” said Webby, who was not involved in the initial detection of the virus but is now working with the team. of Florida on the follow-up. studies.
The virus has become so widespread in birds that it would not be surprising to see the pathogen appear in other unexpected species, he added. “Unfortunately, I think maybe it’s just kind of a sign of what’s going to happen if this virus doesn’t go away,” he added.
Experts stress that the risk to humans remains low. In the United States, the circulating version of the virus 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 spreading the virus to new species poses potential risks to wildlife and gives the virus new chances 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 millions of farmed birds, according to the Department of Agriculture. Compared to previous versions of the virus, this lineage has taken a heavy toll on wild bird populations, taking down eagles, owls, pelicans and more.
This, in turn, has endangered mammals that encounter wild birds. As outbreaks spread this spring, the virus appeared in foxes, bobcats, skunks and other species. The virus has also been blamed for a spike in seal strandings in Maine, where bird flu has been detected in gray and harbor seals.
The Florida dolphin, a young male, was found in March in a canal in Dixie County, where locals noticed the animal had become trapped between the pilings of a pier and a seawall, said Dr. Michael Walsh, a veterinarian at the University of Florida College of Veterinary Medicine who directs the university’s marine animal rescue program.
By the time rescuers arrived, the dolphin was dead, he said. The team, which regularly performs necropsies, collected a variety of samples from the dolphin and stored them until they could be analyzed in more detail.
At the time, scientists had no reason to suspect bird flu had entered the dolphins, and they weren’t particularly in a hurry, said Walsh, who collaborated on the investigation with Dr. Robert Ossiboff, a veterinary pathologist, and Andrew Allison, 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. Scientists have previously documented brain inflammation in virus-infected fox kits, which can cause neurological symptoms in birds and mammals.
Subsequent lab tests revealed the presence of Eurasian H5N1 in the dolphin’s brain and lungs. “The brain tissue really showed a high level of virus,” Walsh said.
Whether the virus contributed to the dolphin’s death remains unknown, as does the precise way the animal contracted it. But it’s not hard to imagine a young dolphin investigating a sick bird near shore, Walsh said, adding, “These animals are always curious about their surroundings and checking things out. So if he came across a sick, dying, or dead bird, he might be very curious about it. He could verbalize it.
The virus was also responsible for the death of a porpoise found stranded in Sweden in June, the Swedish National Veterinary Institute announced last week. The pathogen was found in several organs of the animal, including the brain, according to the agency.
So far, there is no evidence that cetaceans spread the virus to each other, Webby said. And Webby’s team, which isolated and sequenced the virus detected in the Florida dolphin, found no signs that it had developed mutations linked to mammalian adaptation. “It still looks a lot like a virus 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 their toes,” Walsh said. “And that will help us to say how serious this is for cetaceans on the coasts.”
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