A virus that has killed thousands of seals in Denmark, the Netherlands and Sweden appears to be spreading more slowly than expected in Germany, authorities said Wednesday.

Some 100 seals have been found dead on Germany's North Sea coast since mid-July but health authorities in the state of Lower Saxony said the mortality rate appeared to be about normal.

Seven of the 95 animals found showed clear symptoms of the virus and tests were being carried out on four other carcasses, they said.

The state food safety office said the epidemic was spreading much slower than the last epidemic in 1988, which destroyed two-thirds of the North Sea's 25,000-strong seal population.

The disease causes a fatal inflammation of the animals' lungs. The latest outbreak was discovered in Denmark on May 30 and has killed around 2,500 seals.