There are approximately 2800 southern sea otters (Enhydra lutris nereis) all living off the coast of central California and they are listed as threatened under the Endangered Species Act (ESA). Disease organisms coming from terrestrial sources are very significant contributors to mortality and appear to be limiting potential for population recovery. Epidemics and cumulative effects of pathogens and toxins in recent years have resulted in record mortalities. We have attempted to use serosurveys to help determine prevalence and distribution of diseases in the live population.1 Until recently we had found no evidence of serum neutralizing (SN) antibodies to canine, phocine, or cetacean morbilliviruses and assumed that these viruses were not common in the nearshore ecosystems of California which support sea otter populations. However, when additional samples, some of which were duplicates of previous samples, were submitted to another laboratory, detectable and potentially significant (SN) antibody levels were found.
A small number of southern sea otters are maintained in captivity for research or display purposes. One such facility is adjacent to an ecological reserve with an abundant raccoon population, some of which rarely manage to enter the compound containing captive sea otters. The second is a very large public aquarium with a sea otter stranding and response program as well as display animals. Thousands of hours may be spent rehabilitating or raining these animals for behaviors that facilitate minimally invasive research and it is desirable to reduce the risk of debilitating or potentially fatal disease to as close to zero as possible. For these reasons, a three-shot series of a canarypox vectored live recombinant canine distemper vaccine (Purevax™, Merial, Athens, GA, USA), which had been developed for black footed ferrets, was used at the standard dosage 30 days apart. Blood samples were taken at day 0 and at about days 30, 60, 90, and then every 90 days to develop a vaccine response curve. Since this initial work, another five captive sea otters have been vaccinated and we have tracked their antibody response. All animals responded to vaccination by developing SN antibodies and none showed any signs of untoward side effects.
The vaccination of these healthy captive adult sea otters provided an opportunity to compare results of tests for SN antibodies to canine distemper from two laboratories before vaccination and at 30 day and longer intervals thereafter. Results suggest that the two SN tests provide comparable results but have different sensitivities, one appears too insensitive to detect lower titers, the other appears to be too sensitive and thus, subject to false positives, based on current interpretation guidelines.
These studies highlight some of the problems inherent in wildlife serosurveys, the value of comparing results from two or more laboratories, and the value of establishing an antibody response curve for rare species. Currently, available commercial vaccines appear to provide potentially protective SN antibodies and could be used in the event of a canine distemper or similar morbillivirus outbreak in wild otters.
The authors thank Ms. Debbie Brownstein of CDFG-MWVCRC, the staffs of the Marine Mammal Training program at University of California, Santa Cruz, and the Monterey Bay Aquarium particularly Jennifer Coffey, and the Cornell and Oklahoma State Veterinary Diagnostic Laboratories. Funding was provided by the CDFG-OSPR SSEP program.
1. Hanni, K.D., J.A.K. Mazet, F.M.D. Gulland, J. Estes, M. Staedler, M.J. Murray, D.A. Jessup. 2003. Clinical pathological values and assessment of pathogen exposure in southern and Alaskan sea otters. J Wildl Dis. 39(4):837–850.