Abstract

An epizootic of caliciviral disease occurred in a group of semi-domesticated California sea lions (Zalophus californianus) during the months of April and May of 1997. Ten castrated mature male sea lions, ages 12-19 years, were housed in three adjacent open-ocean net enclosures in San Diego Bay (32°42.3'N,117°14.2'W). Four animals (40%) developed oral and extremity vesicles, anorexia, and were reluctant to perform learned behaviors. One animal developed vesicles but maintained a normal appetite and behaviors. The remaining animals showed no clinical signs of infection. Virus was isolated from four of the five animals that developed vesicles. Serum titers to the isolate, a previously untyped calicivirus, were demonstrated in all animals that showed any combination of clinical signs and in one animal that did not show any clinical signs. No virus was isolated from five fecal samples collected from four of the group animals. In all cases where vesicles developed, oral lesions preceded extremity lesions and were more severe. Clinical signs lasted 12-20 days in effected animals. All animals recovered fully from infection.

Viral particles, morphologically indistinguishable from morbillivirus, were also demonstrated on Transmission Electron Microscopy (TEM) of vesicular fluid from the index case. Two animals had measurable serum antibody titers to Phocine Distemper (morbillivirus).