There are two genetically distinct populations of Steller sea lions (Eumetopias jubatus) (SSL) in Alaska, the eastern and western stocks, that are listed under the Endangered Species Act as threatened and endangered respectively. The western stock of Steller sea lions has declined approximately 80% since the late 1970s, while the eastern stock has nearly doubled during the same time period. The cause of the decline is unknown. Possible mechanisms include malnutrition, disease, predation by killer whales, climate changes, exposure to toxic substances, entanglement in marine debris, and incidental and intentional take by humans. Although data to assess each of these possibilities are limited, disease can increase mortality and reproductive failure by causing abortions, still-births or increasing neonatal mortality, all of which can have major impacts on the dynamics of wild populations.
The goal of this study was to identify and characterize SSL herpesviruse(s) throughout Alaska and associate viral genotype and/or viral shedding with the different geographical subpopulations of animals and animal health. A number of clinically important herpesviruses have already been identified in pinnipeds. Phocid herpes virus-1 (PHV-1) has been determined to be responsible for extensive morbidity and mortality in neonatal harbor seal (Phoca vitulina) pups during periods of stress in California. More recently, a herpesvirus has been identified in California sea lions, designated Otarine herpes virus-1 (OtHV-1), and is associated with urogenital carcinoma. Thus studies directed at identifying the presence of herpesviruses in the Alaskan SSL are warranted.
Two hundred and fifty nine swabs were collected between 2001 and 2004 and analyzed for the presence of quality DNA using a polymerase chain reaction (PCR) for SSL interleukin-2; DNA was successfully extracted from 228 swabs from a total of 197 animals. The majority of swabs were nasal (198) with the remaining being from other body parts; some were from lesions (10 total). 126 of the animals were from the Eastern stock, 69 from Prince William Sound and 32 from the Aleutian Islands. A nested PCR, using degenerate group-specific primer sets for herpesviruses, was used to identify the presence of virus in all DNA samples. Three unique herpesviruses were identified in the Eastern Stock: i) 4 identical isolates (designated "C") were from Southwest Brothers, ii) two identical isolates designated as "B" (one from Southwest Brothers and one from West Brothers) and iii) one isolate from Sunset Island designated as "A". Three isolates were identified from animals in Prince William Sound with two designated as "C" and one as "A". Three isolates were identified in the Aleutian Islands with one being "A", one "B" and one indistinguishable from Otarine herpes virus-1 (OtHV-1). While the nested PCR is group-specific and has the potential to identify a broad cross-section of herpes viruses, it is not exceptionally sensitive. PCR's using primers specific for herpes viruses "C", "B" and "A" need to be conducted on all samples to better define the number of animals actually shedding virus. This study has established the presence of significant infection of SSL's with a variety of herpesviruses, some of which may have a catastrophic impact upon animal health.
Supported in part by Morris Animal Foundation, Grant #DO3ZO-68