Mass Die-Off of Caspian Seals Caused by Canine Distemper Virus

Abstract

During the spring of 2000, high death rates were reported in Caspian seals (Phoca caspica) (1), which live only in the Caspian Sea and are listed as a vulnerable species by the International Union for the Conservation of Nature (2).The die-off was first reported near the mouth of the Ural River, Kazakhstan, in late April; it subsequently spread south to the Mangistau region (Figure 1).More than 10,000 seals are estimated to have died during April and May along the Kazakhstan coast.High death rates were also reported in May and June along the Apsheron peninsula of Azerbaijan and the Turkmenistan coast.We present evidence that canine distemper virus infection was the primary cause of these deaths.Clinical signs in infected seals included debilitation, muscle spasms, ocular and nasal exudation, and sneezing.In necropsies performed in June on eight seals from Azerbaijan (Table), no consistent gross lesions were found.However, microscopic lesions, including bronchointerstitial pneumonia, encephalitis, pancreatitis, and lymphocytic depletion in lymphoid tissues, were seen in these and four seals found in Kazakhstan in May.