An unknown virus killed more than 2,300 seals around the Scandinavian coast this summer, local scientists reported last week. The death toll, currently about 14% of the population, is likely to rise further, they say.

The virus attacks the seals' respiratory systems. They suffocate in their own mucus, and most die offshore. Scientists have recently seen breathing difficulties in some small dolphins in the area, suggesting the virus may also be infecting that species.

Tero Hérkénen, a seal researcher at the Swedish Museum of Natural History in Kérna and his colleagues say the outbreak spread from the small Danish island of Anholt to the Skagerrak Strait, which flows between Denmark, Norway and Sweden ? and then up to the Oslo Fjord.

A different virus attacked seals in Northern Europe in 1988 and 2002, wiping out about half of the population on each occasion. ?The dynamics of the spreading of the two viruses are very similar,? says Hérkénen.

Virologists from the National Veterinary Institute in Uppsala, Sweden, are trying to identify the virus from samples taken from four dying seals.