Abstract

Since 1994, when independent investigations reported Brucella antibodies in stranded cetaceans in Britain and bacterial isolation from placentas collected from captive bottlenose dolphin (Tursiops truncatus) in California, efforts have been underway to investigate the epidemiology and pathology of brucellosis in pinnipeds and cetaceans (Ewalt et al. 1994). In the Pacific Northwest, infection was initially documented in harbor seals by serology in 1993. Since that time, there have been ongoing serosurveys of live healthy wild stocks at multiple geographic sites in Washington and Oregon and Southern British Columbia Canada to screen for antibodies to Brucella spp using conventional, terrestrial animal validated methods (BAPA, Card and Rivanol using B. abortus). Since 1993, a total of 1250 harbor seals have been screened during ongoing live healthy capture operations. Fourteen percent of all screened seals have had positive or suspect test results for Brucella titres. Evidence of Brucella exposure was significantly higher among weaned pups/yearlings (54%) and subadults (34%) harbor seals, compared to pups (7%) and adults (8%). The first Brucella spp. culture from a harbor seal in the Pacific Northwest was in 1996 and currently Brucella has been isolated or confirmed by polymerase chain reaction (with universal Brucella spp primers) on twenty harbour seals from Washington State. In 1997, immunohistochemistry of representative tissues disclosed coccobacilli within the uteri of Parafilaroides lungworms (Garner, M.M. et al. 1997). Increased funding in 2004 through the Prescott Grant provided resources to enhance collection of serum and tissue samples from stranded marine mammals. Most samples have been collected from harbor seals, though other marine mammal groups have been screened.

From an epidemiologic perspective, seropositive and/or culture positive harbor seals were most frequently identified from November through to February and comprised predominantly young of year and subadults, with a low percentage of suspect and positive Brucella antibodies in neonates and adults. At present, there is insufficient data to speculate on what may account for these age-class related differences. In contrast to cetaceans, anecdotal evidence suggests that there is no consistent pathology, which may be directly attributed to Brucella spp infection in harbor seals. It is possible that this bacterium is host adapted in this species of pinniped. With anticipated renewed funding through Prescott and collaboration with investigators from the east coast, efforts to further resolve the pathogenesis and epidemiology of infection are anticipated and additional information should be forthcoming.