In the USA, there has been a mass extinction among seals in the wake of the currently circulating bird flu. In New England in the northeast of the USA, hundreds of seals and grey seals have died of H5N1, reports a research team from Tufts University in Medford (USA) in the journal "Emerging Infectious Diseases".

For some time now, the most severe bird flu epidemic ever documented has been rampant among birds. It extends over several continents. Tens of millions of animals have already died, especially seabirds.

3500 sea lions died in Peru

It is known that the circulating H5N1 development line also infects and kills mammals such as minks, foxes, raccoons, martens and bears. In most cases, these are individual proofs.

In Peru, however, according to Tufts University, about 3500 sea lions recently died of the virus, Canada reported a seal death at the mouth of St. Lawrence. In addition, there have been reports from Russia about a similar event in seals in the Caspian Sea.

The team led by Wendy Puryear and Kaitlin Sawatzki has now evaluated data on pathogen analyses of samples from dead, sick, but also healthy animals.

Avian flu had been continuously monitored with tests in birds and some mammals in New England since January 2022. Accordingly, in June and July 2022 alone, more than 330 seals and grey seals died along the North Atlantic coast at bird flu line

Transmission by gulls?

At the time of seal death in New England, the virus also hit seagulls particularly hard, the scientists explain. Sometimes there are samples in pairs, 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 excrement of a sick bird or with water contaminated by it, or if it eats an infected bird.

It is well known that H5N1 is almost 100 percent fatal 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 of sampling or succumbed to the pathogen shortly thereafter.

The question of whether the virus is also transmitted between seals is still being discussed. "It wouldn't be surprising if there could be transmission between seals, as this was already the case with low-pathogenic bird flu," Puryear said. However, definitive evidence is still lacking - for seals and generally for mammalian-to-mammal transmission.

Experts are concerned that the virus could adapt better to mammals and thus also to humans. So far, only one death in China has been proven to be attributed to the currently circulating group of bird flu viruses. In the case of the woman who died in October, the H5N1 virus of group had been detected, the Friedrich-Loeffler-Institut (FLI) had recently announced. She was 38 years old and had contact with infected domestic poultry. She contracted severe pneumonia and died in hospital.

Experts were worried about an outbreak of bird flu on a Spanish mink farm in October 2022. There are indications in the animals that the pathogen has genetically adapted better to mammals, it said. Whether there were transmissions from animal to animal in the farm or another route of infection, for example via food, is still unclear. Mammalian-to-mammalian transmission would pose a higher risk to humans.