Abstract

During the period of August 1995 to August 1997, six of eighteen common dolphins (Delphinus delphis) that stranded along the southern California coast tested antibody positive for dolphin morbillivirus (DMV). The titers ranged from 1:50 to 1:910 by the method of virus neutralization. Comparable changes were also recorded with rinderpest N-protein virus ELISA titers using serum samples collected from three of these six animals. VN titers were negative to canine (CDV) and phocine (PDV) distemper virus, and slightly positive to porpoise morbillivirus (PMV), suggesting that the virus which infected these individuals was similar to DMV and PMV.

The first dolphin that tested positive for DMV stranded on August 21, 1995, in Marina del Rey, California (N33°56';W118°28'), and was taken to Sea World of California, where she was treated for pneumonia. At presentation, the dolphin's VN titer was 1:50 which rose to 1:140 by day nine. By October 30, 1995, the titer stabilized at 1:720, 70 days after presentation. Similarly, the presenting ELISA titer was 1:25 which stabilized at 1:100.

On October 9, 1995, whole blood tested negative by polymerase chain reaction for dolphin morbillivirus. Believing that the common dolphin was aviremic and unable to shed virus, it was decided to introduce a 15 year old Atlantic bottlenose dolphin (Tursiops truncatus) and a 28 year old Pacific white-sided dolphin (Lagenorhynchus obliquidens) on May 4, 1996. The three lived together in a 760,000 liter pool for 167 days. Each were monitored by CBC/chemistries and VN for morbillivirus infection at regular intervals. Both of the introduced dolphins remained healthy and neither seroconverted during this period, while the common dolphin's VN and ELISA titer remained stable over the next five months. On October 16, 1996, 14 months after stranding, the common dolphin was reintroduced to the Pacific Ocean.

Histopathologic examination of tissues from the other five antibody positive dolphins did not demonstrate lesions characteristic of morbilliviral disease, however morbilliviral RNA was detected in three of the five by RT-PCR. Although the number of dolphins in this study is relatively small, evidence of infection in 33% suggests that morbilliviral infection may be frequent in common dolphins.