Canine distemper virus (CDV) has been identified as the most likely cause of a die-off of thousands of seals in the Caspian Sea earlier this year. Although the findings by two independent research groups allay fears of a threat to humans, they heighten concerns about the survival of the imperiled species.
Dead and dying seals began washing ashore in mid-April near the mouth of the Ural River in Kazakhstan, one of five countries bordering the Caspian sea. Normally shy, the small, mottled-gray seals would swim up to boats, rub their noses against the hull, and bark oddly, as if gasping for air, says Anatoly Beklemishev, a molecular biologist with the State Research Center of Virology and Biotechnology (VECTOR) near Novosibirsk, Russia.
Environmental groups immediately pointed a finger at oil companies in the region, claiming that sulfur dioxide discharges were corroding the animals' lungs. In June, Kazakhstan's environment minister asserted that pollution from the oil fields and pesticides were degrading the seals' health, citing recent studies showing high levels of DDT, an organochloride pesticide, in Caspian seal blubber. But the companies have denied the charges, and scientists say that DDT alone could not account for the seal deaths.
Working with tissue samples from 16 seals, a team led by Seamus Kennedy of the Department of Agriculture and Rural Development in Belfast, U.K., found lung tissue and epithelial cells riddled with microscopic lesions characteristic of morbillivirus infection--the viral group that includes CDV and a pathogen recently discovered in seals, phocine distemper virus. The researchers nailed canine distemper using a polymerase chain reaction (PCR) test specific for a CDV gene.
The findings will appear in the November-December issue of Emerging Infectious Diseases. However, they were posted last week on the journal's Web site after a Russian-Kazakh team released its preliminary findings. That group, led by Beklemishev and Aleksandr Shestopalov of VECTOR, took samples from seals at a rookery on Maly Zhemchuzhny Island off the Russian coast and from a rookery on Kazakhstan's Bautin Bay.
The die-off, which has subsided after claiming as many as 20,000 victims, is another blow to the long-term prospects for the Caspian seal, a population of around 400,000 animals that is listed by the World Conservation Union as vulnerable to extinction. Scientists also plan to keep a close eye on the seals by watching them on the ice throughout the winter. "Just how high the mortality will be is anybody's guess," says Kennedy.