There has been a mass death among seals in the United States as a result of the bird flu that is currently circulating. A research team from Tufts University in Medford (USA) reports in the journal "Emerging Infectious Diseases" that hundreds of harbor seals and gray seals have died from H5N1 in New England in the north-east of the USA.
For some time now, the worst bird flu wave ever documented has been rampant among birds. It extends over several continents. Tens of millions of animals have already died, particularly seabirds. It is known that the circulating H5N1 lineage 184.108.40.206b also infects and kills mammals such as mink, foxes, raccoons, martens and bears. Most of the time, these are individual proofs.
In Peru, however, according to Tufts University, around 3,500 sea lions recently died from the virus, and Canada reported a seal death at the St. Lawrence estuary. There have also been reports from Russia of a similar event in seals in the Caspian Sea.
The team led by Wendy Puryear and Kaitlin Sawatzki now evaluated data on pathogen analyzes from samples from dead, sick and healthy animals. Avian influenza had been monitored with testing in birds and some mammals in New England since January 2022. According to this, in June and July 2022 alone, more than 330 harbor and gray seals died from bird flu line 220.127.116.11b along the North Atlantic coast.
At the time the seals were dying in New England, the virus was also hitting seagulls particularly hard, the scientists explain. Sometimes there are pairs of samples, sometimes literally from a bird and a seal on the same beach, Puryear explained. A seal can become infected if it comes into contact with a sick bird's droppings or water contaminated by it, or if it eats an infected bird.
It is known that H5N1 is almost 100 percent deadly in waterfowl. The study now shows that this could also apply to mammals: all seals that tested positive for the virus were already dead at the time the sample was taken or succumbed to the pathogen shortly afterwards.
The question of whether the virus is also transmitted between seals is still being discussed. "It wouldn't be surprising if transmission between seals could occur, as this has already happened with low pathogenic avian influenza," Puryear said. However, definitive evidence is still lacking – for seals and generally for transmission from mammal to mammal.
Experts are concerned that the virus could adapt better to mammals and thus to humans. So far, only one death in China has been proven to be attributed to the currently circulating group of avian flu viruses. The Friedrich Loeffler Institute (FLI) recently reported that the woman who died in October had the H5N1 virus of group 18.104.22.168b. She was 38 years old and had contact with infected poultry. She developed severe pneumonia and died in hospital.
Experts were concerned about an outbreak of bird flu on a Spanish mink farm in October 2022. There were indications in the animals that the pathogen had adapted genetically better to mammals, it said. It is not yet clear whether there was transmission from animal to animal in the farm or another route of infection, for example via food. Mammal-to-mammal transmission would pose a higher risk to humans.