Caspian Seals Dying of Virus Infection

PORTAFERRY, Northern Ireland, September 20, 2000 (ENS) - Thousands of Caspian seals have died in the Caspian Sea since April 2000. An international team of scientists, working as part of the Caspian Environment Program's Ecotoxicology Project (ECOTOX), has now concluded canine distemper virus infection was the primary cause of this die-off.

The Caspian seal is listed as Vulnerable on the World Conservation Union-IUCN Red List. From April to June over 11,000 Caspian seals were found dead along the Kazakhstan coast and an unknown number of dead seals were also reported from the Russian, Azerbaijan and Turkmenistan sectors of the Caspian Sea. Reports of an increased mortality rate were still being received as late as August.

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Caspian seals can live to up 50 years old. (Photos by Pavel Prosyanov, KaspNIRH, courtesy Seal Conservation Society)
The seal population is facing severe problems due to heavy pollution of the Caspian Sea by pesticides and industrial pollutants. Studies are underway to determine the potential role of pollution in the recent seal deaths which are still continuing in some areas of the Caspian Sea.

Numerous possible contributors to seal mortality have been investigated in the past, including pollution from land based sources, climatic effects such as absence of ice in the North Caspian Sea, parasitic worms, and other disease carriers.

In 1997, a single Caspian seal was determined to have canine distemper virus infection, but seal disease could not then be attributed directly to this virus. A post-mortem investigation in 1997 found extraordinarily high levels of the pesticide DDT in seal tissues along with the presence of canine distemper virus, and an infertility rate in adult females of more than 70 percent.

The ECOTOX study was designed to examine the large number of recent deaths in Caspian seals with these various causes in mind.

The Caspian Sea is bordered by Russia, Kazakhstan, Azerbaijan, Iran and Turkmenistan. Scientists from across Europe contributed to this seal mortality study.

Workers from the Institute of Zoology, Regents Park, London, the Seal Rehabilitation and Research Center, Pieterburen, The Netherlands, the Sea Mammal Research Unit, University of St. Andrews, Scotland and the Tara Seal Research Centre, Portaferry, Northern Ireland, visited areas where seals had died in Kazakhstan and Azerbaijan during May and June 2000.

They collected tissue and blood samples from 16 dead seals.

They worked in collaboration with staff from the Geological Institute of the Azerbaijan Republic Academy of Sciences, Baku, Azerbaijan; the Laboratory of Virus Ecology, Institute of Microbiology and Virology, Almaty, Kazakhstan; and Akademgorodok, Institute of Zoology, Almaty, Kazakhstan.

seals Microscopic lesions, characteristic of canine distemper, were found in the seal tissues and infection with canine distemper virus was confirmed by serological and molecular methods.

These findings in seals from several geographically dispersed regions of the Caspian Sea provide strong evidence that canine distemper virus infection was the primary cause of the disease outbreak.

The results of these investigations, which were supported by the World Bank through a donation by a Japanese Trust Fund, and by the Offshore Kazakhstan International Operating Company, have been subjected to peer review.

The results of this investigation have been accepted for publication in a forthcoming issue of the journal "Emerging Infectious Diseases."