Vaccination success convicts seal killer.

Vaccination success convicts seal killer

In the first scientific test in seals of two vaccines for canine distemper virus (CDV), Dutch scientists have successfully inoculated six of the animals. The work constitutes the "final proof" that either CDV or the closely related phocine distemper virus caused the deaths of thousands of seals in the North and Baltic seas in an epidemic that began last April (SN: 9/3/88, p.149), says study leader Alfred D.M.E. Osterhaus of the Dutch National Institute of Public Health and Environmental Protection in Bilthoven.

The Dutch team vaccinated six harbor seals with either a whole dead virus or a substance made from two CDV proteins that has been shown to prevent the disease in dogs. Two other seals received a sham vaccine. The seals, which had been kept in isolation for many years, had shown no signs of the disease and carried no antibodies to CDV before the experiment. But when tested after the third inoculation, the six given the vaccine had developed a significant number of antibodies to CDV.

Ten days later, the scientists put all eight seals into a pool infested with cells from the spleen and lungs of seals that had died during the outbreak, a procedure that causes CDV symptons in dogs. As a result, the two sham-vaccinated seals developed signs of CDV, such as respiratory problems, nasal discharge and general lethargy. Both died within three weeks. No clinical signs of the disease appeared in the vaccinated animals, the scientists report.

"Although the number of animals studied is small, the data warrant the conclusion that seals can be protected from phocid distemper [or CDV] by vaccination with certain inactivated CDV vaccines," they write in a Jan. 5 letter to NATURE. The vaccines have already been distributed to aquariums, zoos and sanctuaries, some of which had been using them before they were proven to work, Osterhaus says. He adds that the immune-inducing substances are not meant for wild seals because of practical difficulties in administering them.

Although the death rate has leveled off, seals continue to fall victim to the virus. The death toll to date is estimated at 17,000 -- 60 to 80 percent of the total number of seals that formerly lived off the coasts of Denmark, Germany, the Netherlands and Great Britain, Osterhaus says. Most dies in the first two weeks of the epidemic.