A bottlenose dolphin in Florida and a porpoise in Sweden have tested positive for a highly virulent strain of bird flu, marking the first documented cases of avian influenza in cetaceans.
The infections come amid an “unprecedented” season of H5N1 bird flu, which has killed millions of wild birds and poultry across the globe and is now seeping into a broad array of other species, including seals, foxes and skunks.
The latest findings in cetaceans – a group of marine mammals that includes dolphins, porpoises and whales – are the first documented. Experts said it demonstrated both the risks posed to wildlife, and provides a new opportunity for the virus to mutate and adapt.
In spring, a young male bottlenose dolphin was found trapped in a canal in Florida, but had died before the rescue team arrived. The scientists collected samples and later detected H5N1 in the dolphin’s brains and lungs.
The results, announced by the University of Florida, come after officials at the Swedish National Veterinary Institute said the virus was responsible for a porpoise found stranded in June. Laboratory tests found bird flu in several of the animal’s organs, including the brain.
Cross-species transmission
Dr Richard Webby, an influenza virologist at St Jude Children’s Research Hospital in Tennessee, US, said the discovery of the highly pathogenic bird flu virus in a dolphin and a porpoise two continents apart suggests these cases are not a “one-off, unique event”.
Dr Andrew Suggitt, an ecologist at Northumbria University, added that we “shouldn’t be too surprised” that avian influenza has crossed to other species, given the scale of the outbreak this year.
As of August, the European Centre for Disease Control had reported that more than 22 million cases had been detected in poultry and wild birds since October, double last season.
The outbreak has hit wild birds especially hard. In the UK at least 300 outbreaks in seabird colonies have been reported, while the National Trust has warned up to 50,000 birds are likely to have died in the Farne Islands, off the coast of Northumberland.
“Dolphins, porpoises and other cetaceans will be encountering dead or dying birds in marine and coastal habitats, and a proportion will interact with the carcasses and become infected themselves,” Dr Suggit told The Telegraph.
He added that although surveillance efforts should be ramped up, the risk to humans remains low. Since 2003, roughly 860 cases of H5N1 have been found in people across the globe, and 456 people have died of the virus. The only case reported in the UK was in January, in a duck farmer in Devon called Alan Gosling.
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