Bird flu isn’t just lurking inside cows, new research shows. Florida scientists have reported the first known case of highly pathogenic H5N1 avian influenza in a common bottlenose dolphin (Tursiops truncatus). Though the case dates back to 2022, it’s the latest indication that these flu strains can potentially infect a wide variety of mammals.
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The report was published Friday in the Nature journal Communications Biology. According to the paper, the flu-infected dolphin was first identified on March 29, 2022. Researchers with the University of Florida’s Marine Animal Rescue Program were notified of a dolphin that appeared to be in clear distress around the waters of Horseshoe Beach in North Florida. By the time they arrived, however, the dolphin had already died. It was subsequently packed in ice and taken to the university for an autopsy the following day.
The post-mortem examination found clear signs of poor health and inflammation in the dolphin’s brain and meninges (the membrane layers that protect the brain and spinal cord). The dolphin tested negative for other common infectious causes of brain inflammation, which prompted the researchers to expand their search. They knew that wild birds can develop neuroinflammation from highly pathogenic strains of avian influenza, that several bird die-offs tied to the flu had occurred in the area recently, and that recent outbreaks had occurred among other populations of marine mammals elsewhere, so they decided to screen for it. Testing then revealed the presence of H5N1 within the dolphin’s lungs and brain.
There have been sightings of highly pathogenic avian influenza (HPAI) in other marine mammals lately, such as harbor seals and other species of dolphins. But this is the first reported case documented in a common bottlenose dolphin and the first report in any cetacean (dolphins and whales) within the waters of North America.
Strains of bird flu are classified as highly pathogenic when they cause severe illness and deaths in wild birds, so it’s not necessarily a given that they will be as dangerous to other animals they infect. The current outbreaks of H5N1 bird flu in cows, for instance, have caused generally mild illness to date. But strains belonging to this particular lineage of H5N1 (2.3.4.4b) have been deadly to marine mammals.
The strain in this case did not appear to develop known genetic changes that would make it easier to infect and transmit between mammals, the authors found. But flu viruses mutate very quickly, leaving open the possibility that some strains will adapt and pick up the right changes that can make them a much bigger threat to mammals both on land and in the sea.
“Human health risk aside, the consequences of A(H5N1) viruses adapting for enhanced replication in and transmission between dolphins and other cetacea could be catastrophic for these populations,” the authors wrote.
The researchers are continuing to investigate the case, hoping to pinpoint the origins of the dolphin’s infection and to better understand the potential for bird flu strains to successfully jump the species barrier to these marine mammals.
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