Immune responses in common and grey seals during the seal epizootic.

Serological surveys of common and grey seals were performed to monitor the spread of the phocid distemper outbreak in 1988 and its effects on the host immune response. The disease affected mainly common seals; grey seals were largely unaffected but did have anti-CDV antibodies which developed during 1988. Canadian seals, both common and grey, showed evidence of a morbillivirus infection but without the apparent mortality observed in British common seals. Common seal circulating immunoglobulin levels were not greatly affected during the outbreak, although there was some reduction in the most severely affected pups. Vaccination of common seals with CDV antigens elicited high titres of antibodies and produced clinical protection. Vertical transmission of host immunity was shown in grey seals although the longevity of protection has not been determined. The large population of common seals which are not immune emphasises that such an epizootic could have serious consequences again in the future.