The following websites contain information about a current outbreak of
PDV among European harbour seal populations.
Information on dead seals in the Kattegat
Report in New Scientist:
Text of New Scientist report:
Deadly seal virus strikes Europe again
13:35 31 May 02
NewScientist.com news service
A virus that wiped out half of western Europe's seal population in 1988
has struck again. At least 250 seals have died in Denmark, and initial tests suggest the virus has spread to Sweden. Marine biologists fear the death toll will soar.
Phocine distemper virus (PDV) spreads quickly through harbour seal populations, attacking the immune system. Pneumonia is the most common cause of death after infection.
"Naturally we fear an epidemic similar to the one we had in 1988 and we can't do much to stop it from spreading since there's no vaccine or treatment," says Hans Henrik Dietz, head of research at Denmark's State Veterinary Institute.
Suspicious harbour seal deaths were first reported on the islands of Anholt and Laesoe in the Kattegat Channel between Denmark and Sweden a month ago. "We examined 17 of these mammals and most showed the same symptoms as those that died in 1988 from the virus that killed 4000 seals in Denmark," says Dietz.
At least 20 dead seals have washed up on the south-western coast of Sweden since Wednesday. "We are very concerned now. We are prepared for the worst," Anne Roos of the Contamination Research Group at the Swedish Museum of Natural History told New Scientist.
An autopsy of one of the dead seals in Sweden revealed it died from severe pneumonia. "We are now employing more people to be alert on the western coast and to conduct more autopsies," says Roos.
PDV was first identified in April 1988, when widespread harbour seal abortions and deaths were reported in the Kattegat area. The virus spread rapidly to the North Sea, the Wadden Sea and the Baltic Sea, killing between 17,000 and 20,000 seals in north-western Europe in eight months.
The population has bounced back. "Today there are about 15,000 harbour seals in the waters around Sweden and Denmark - more than there were before the outbreak," says Roos.
Some of these seals will be survivors of the 1988 outbreak and could be immune to PDV - but scientists have no idea how many. "In 1992, a study found that 20 per cent of harbour seals tested around Sweden had antibodies to the virus. But there will of course be fewer now," says Roos.
But the rebound in population could itself partly explain the new outbreak, says Seamus Kennedy of the Northern Ireland Veterinary Sciences Division in Belfast. Kennedy's lab was the first to identify PDV in 1988.
"Distemper viruses are present in several marine mammal populations. It could be that an outbreak in seals is triggered when the population density exceeds a threshold level, and the virus is introduced into non-immune population," he says.
PDV is closely related to canine distemper virus, but no-one knows where it comes from. Harbour seals seem to be particularly vulnerable. They accounted for the vast majority of the deaths associated with the 1988 outbreak, although harp seals and grey seals were also affected.
Historical records suggest that PDV has caused mass seal deaths in the past, says Kennedy: "I suspect it has been in the marine mammal population for centuries. In 1955 in Antarctica, a large number of crab-eater seals died. If you read the old papers you get the impression that could have been an outbreak of seal distemper."
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