The serological response of the common seal (Phoca vitulina) and the grey seal (Halichoerus grypus) to phocine distemper virus as measured by a canine distemper virus neutralisation test.

The application of a canine distemper virus (CDV) neutralisation test revealed that antibody titres of up to 11,620 were present in the sera of common seals during the epizootic of phocine distemper in British waters. However, during the later stages of the epizootic and afterwards, a surprisingly high proportion of animals were still seronegative. Titres of from 90 to 183 were common in diseased animals and were probably indicative of partial immunosuppression. A few animals with proven phocine distemper had titres of less than 64, this being evidence of a more profound immunosuppression. Recovered animals tended to have moderate to high titres and in some cases these persisted for at least 6.5 months. By contrast, the administration of an inactivated CDV vaccine produced antibody which declined rapidly to very low levels within the same period. Infection also occurred in grey seals in 1988 but without severe mortality. Antibody titres in this species nearly always lay in the range 128-734 and persisted at or around this level for at least 12 months. In both common and grey seals, antibody was transferred by suckling from mother to pup but absorption by the pup seemed to take place more slowly than in domestic mammals.