We report evidence of enzootic morbillivirus infection among long-finned, Globicephala melas, and short-finned, G. macrorhynchus, pilot whales in the western Atlantic. A retrospective serologic survey, using five morbilliviruses, was carried out on 99 G. melas from 14 stranding events between 1982 and 1993 and from 25 G. macrorhynchus stranded in 5 events between 1986 and 1994. A blood sample was also obtained from an adult G. melas by-caught in the western North Atlantic. Tissues were collected from 24 G. melas and 15 G. macrorhynchus for histology and immunoperoxidase staining. Neutralizing antibody titers were found in 92 (92%) of 100 G. melas and 16 (64%) of 25 G. macrorynchus, and titers were highest against cetacean morbilliviruses. Seroprevalence was similar between age classes and sexes. The earliest evidence of infection was in a G. melas that stranded in 1982. Stable antibody titers were observed in pilot whales under rehabilitation for up to eight months. Clinical disease consistent with morbillivirus pneumonia was detected in a G. melas calf. Immunoperoxidase staining confirmed that viral antigen was present in the lesions.
We propose that enzootic infection in pilot whales is facilitated by population size, social structure, and migration patterns. Furthermore, through mixing with other odontocetes, pilot whales could act as vectors through the Atlantic. Clinical morbillivirus infection may precipitate mass strandings of highly social odontocetes.