We have detected serologic evidence of morbillivirus infection in 14 of 18 odontocete species from the western Atlantic and Gulf of Mexico. For all animals, antibody titers were similar against porpoise morbillivirus (PMV) and dolphin morbillivirus (DMV) and higher than those against any other morbillivirus. Immunoprecipitation studies using radio-labeled canine distemper virus antigen and serum from ten cetacean species were carried out to determine the specificity of the immune response. A retrospective serologic study was carried out on long-finned (n = 99) and short-finned (n = 25) pilot whales (Globicephala melas and G. macrorhynchus) stranded in 19 events between 1982 and 1994. In addition, a blood sample was obtained from a free-ranging long-finned pilot whale by-caught in fishing gear. Tissues were collected from 24 stranded G. melas and 15 G. macrorhynchus for histo-pathology and immuno-histochemistry. Morbillivirus neutralizing antibodies were found in 92% of G. melas and 64% of G. macrorhynchus. Serum from sero-positive whales showed precipitation of the nucleocapsid (N) protein of CDV confirming exposure to a morbillivirus. Seroprevalence was similar between age classes and sexes and the earliest evidence of infection was in a long-finned pilot whale that stranded in 1982. Clinical disease consistent with morbillivirus pneumonia was detected in a G. melas calf stranded on Cape Cod in September 1989. Immunoperoxidase staining confirmed that morbillivirus antigen was present in the lung lesions. Stable antibody titers were observed in juvenile pilot whales under rehabilitation for up to 8 months.

Our data suggest that morbillivirus infection is enzootic among pilot whales. We propose that the population size, social structure, and migration patterns of pilot whales facilitate maintenance of infection. Furthermore, through mixing with other odontocetes, they could act as vectors of infection both in the wild and in captivity. We encourage the investigation of clinical morbillivirus infection as a possible cause of mass strandings among highly social odontocetes.