A Comparison of Four Serologic Assays in Screening for Brucella Exposure in Hawaiian Monk Seals

Abstract

A survey for Brucella spp. antibodies was undertaken on 164 serum samples from 144 Hawaiian monk seals (Monachus schauinslandi) from the northwestern Hawaiian Islands collected between 1995 and 2002. The buffered antigen plate agglutination test (BPAT), the indirect enzyme immunoassay (I-ELISA), the competitive enzyme immunoassay (C-ELISA), and the fluorescence polarization assay (FPA) were compared with regard to their ability in detecting antibodies to Brucella spp. in the serum samples. Overall, antibodies were detected in 28 (17.1%) animals, using the BPAT test, 25 (15.2%) by the C-ELISA, and 19 (11.6%) in the I-ELISA and the FPA test, using thresholds established for cattle. No evidence of gross pathology consistent with clinical brucellosis was noted in any of the seropositive animals tested. Although further work would be necessary to validate these tests for use with monk seals it appears that both the C-ELISA and the FPA tests would be appropriate as diagnostic screening tests for detection of antibodies to Brucella spp. in this species.

Epizootiology of Brucella Infection in Australian Fur Seals

“…and those to other crossreacting gram-negative bacteria (Nielsen, 1990;Samartino et al, 1999). Whether the cELISA behaves similarly in pinnipeds is unknown, but our study is consistent with findings in Hawaiian monk seals (Monachus schauinslandi), in which it was concluded that the iELISA was an unreliable test for the identification of Brucella antibody-positive individuals (Nielsen et al, 2005). The FPA returned the fewest number of positive results; this is also consistent with Nielsen et al (2005), who suggested that the FPA is significantly more specific than the iELISA and marginally more specific than the cELISA.…”

“…Additionally, all juvenile and adult female samples plus sera from 10 pups from each year were tested by a second cELISA, an indirect ELISA (iELISA), and a fluorescence polarization assay (FPA) at the Canadian Food Inspection Laboratories (Ottawa, Canada), so that test performance and agreement could be assessed. Although these tests have been used to investigate Brucella antibody status in marine mammals (Nielsen et al, 2005), they have not been validated for this purpose.…”

“…The second cELISA, the iELISA, and the FPA were performed according to the methods described by Nielsen et al (2005). For the cELISA, an inhibition value of $30% was considered a positive result.…”

“…For the iELISA, inhibition of binding $20% was considered positive. On the basis of previous experiments with seal sera (Nielsen et al, 2005), a cutoff millipolarization value of $90 mP was used to indicate a positive FPA.…”

“…has been recognized since the mid-1990s (Ross et al, 1994). Subsequently, serologic evidence of exposure to bacteria of this genus has been found in many species from various geographic areas (Nielsen et al, 2001;Tryland et al, 2005). Marine strains of Brucella are genetically and biochemically distinct from other species in this genus, and isolates from cetaceans and pinnipeds have been proposed recently as two new species, respectively, Brucella ceti and Brucella pinnipedialis (Foster et al, 2007;Dawson et al, 2008b).…”