Europes frigid North Sea typically shelters a healthy population of migratory harbor seals. In 1988, however, an attack of the phocine distemper virus all but wiped out the group, dumping 18,000 seal carcasses along the beaches of northern Europe within the year. Scientists thought the population might never recover, but it bounced back from its post-outbreak size of 4,000 individuals in 1989 to 17,000 in 2000. For the past 10 years, investigators could find no sign of this devastating disease, offering hope that it had disappeared completely. But that optimism, it seems, was premature. Researchers writing today in the journal Science report that the epidemic is beginning anew.

This past May, an unusually high number of seals seemed to be dying on Anholt, an island off the coast of Denmark where the first outbreak began 14 years ago. Since then, hundreds of animals have presented respiratory and nervous system symptoms common to the phocine distemper virus. Subsequent detection of the viruss DNA and antiviral antibodies in the carcasses, say Trine Jensen of the Seal Rehabilitation and Research Center in Pieterburen, Netherlands and his colleagues, confirmed that the long-lost disease has in fact re-emerged. Indeed, it has already begun to spread. Dead animals have turned up in Sweden, and most recently in the Netherlands, paralleling the progression of the previous epidemic. The rapid spread is a result of the seals speedy swimming: traveling hundreds of kilometers in just a few days and mingling with other seals along the way, these marine mammals are unwittingly contributing to their own demise.

The scientists state that at least 20 percent of the seals have some immunity to the virus from the last epidemic, and will thus survive this one. But whether or not humans can help minimize the number of deaths among the rest of the animals is unclear. "The responsible ministries and nongovernmental organizations of the respective countries involved are now discussing preparations for the possible consequences if history is repeated," the authors write. Hopefully, idly standing by is not the only option.