Abstract

Unique strains of Brucella were first identified in marine mammals in 1994. Since then, studies have been done to assess seroprevalence and potential health effects in many species, but have been hampered by the lack of sensitivity and/or specificity of traditional serologic tests for marine strains of Brucella. Additionally, postmortem diagnoses are classically based on culture of this fastidious pathogen, which poses a risk to laboratory personnel. As part of a comprehensive survey of marine mammal populations, several diagnostic tests have been developed specifically for the detection of exposure to, or presence of, marine Brucella sp. in serum or tissue samples. These include a competitive ELISA using a marine Brucella antigen, a genus-specific multiplex real-time PCR assay, and an immunohistochemical staining technique using polyclonal antibody to a marine Brucella sp. These tests, in addition to microbiologic culture, are being used to analyze cetacean, pinniped, and mustelid tissue and blood samples from wild and captive populations. Preliminary data have been collected on a subset of animals tested by at least two methods, and which are positive by at least one of these tests. No one technique has been able to identify Brucella in all cases. In these animals, real-time PCR identified Brucella in 82% (14/17), compared to 88% (7/8) by immunohistochemistry, 75% (12/16) by culture, and 70% (7/10) by cELISA serology. A combination of culture and PCR identified Brucella in 100% (n=18) of animals. These preliminary results indicate the benefits of a multifaceted approach to diagnosis of brucellosis in marine mammals.