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SHORT COMMUNICATION |
1 Department of Applied Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan;
2 Department of Basic Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Hokkaido 080-8555, Japan;
3 Department of Wildlife Science, College of Bioresource Sciences, Nihon University, Fujisawa, Kanagawa 252-8510, Japan;
4 Hammond Consultants Inc., 1881 Rouge River Circle, Ventura, California 93004, USA
5 Corresponding author (email: watarai{at}obihiro.ac.jp)
ABSTRACT:
Brucella spp. have been recently isolated from a variety of marine mammals. Serum samples from 58 Pacific bottlenose dolphins (Tursipa aduncus) from the Solomon Islands were tested for antibodies to Brucella spp. by the tube agglutination test (TAT), enzymed-linked immunosorbent assay (ELISA), and immunoblotting. Anti-Brucella spp. antibodies were detected by TAT and ELISA in 31 and 40 of 58 samples, respectively. These results suggest that Pacific bottlenose dolphins from the Solomon Islands are infected with Brucella spp. or a Brucella-like organism.
Key words: Bottlenose dolphin, Brucella, Solomon Islands.
Brucellosis is a serious debilitating disease in humans and an important cause of abortion and sterility in domestic animals. Brucella spp. are facultative, gram-negative, intracellular bacteria and the etiologic agent of brucellosis, a widely distributed zoonosis (Ko and Splitter, 2003). The establishment of chronic infection depends on the ability of brucellae to survive within phagocytes (Harmon et al., 1988). The host range for Brucella spp. has recently expanded to include marine mammals, and anti-Brucella antibodies have been detected in cetaceans and pinnipeds around Europe and North and South America as well as the Arctic Sea (Nielsen et al., 1996; Ross et al., 1996; Garner et al., 1997; Jepson et al., 1997; Tryland et al., 1999; Forbes et al., 2000; Retamal et al., 2000; Van Bressem et al., 2001; Ohishi et al., 2003).
In this study we tested Pacific bottle-nose dolphins (Tursiops aduncus) from the Solomon Islands for antibodies to Brucella spp. Serum samples were obtained from 58 Pacific bottlenose dolphins captured in 2003 at Gavutu Island, Solomon Islands (9u7'S, 160u10.6'E). Blood samples were taken with the approval of the Solomon Islands government and with Animal Care and Use approval in the Solomon Islands (Omata et al., 2005). All dolphins were captured with nets as described (Geraci and Lounsbury, 1993); all animals remained alive and were later released or used in a dolphin swim program.
The tube agglutination test (TAT) was used for the detection of anti-Brucella antibodies. An antibody titer of 
40 is regarded as positive (100 international units/ml) in testing of domestic animals. Serum samples were also tested by ELISA and immunoblotting as described previously (Erdenebaatar et al., 2003). For ELISA, the positive threshold value was set as the lowest absorbance value (OD492=0.4) observed for serum samples testing positive by TAT at dilutions of 1:40. An absorbance of higher than this at a dilution ratio 1:40 was regarded as positive, and all samples were diluted to endpoint. Antibodies to Brucella were detected by TAT in 31 of 58 serum samples and by ELISA in 40 of 58 serum samples that tested positive. ELISA absorbance values for 18 of the TAT-negative samples ranged between 0.05 and 0.40 for all dilutions. In the remaining nine TAT-negative samples, absorbance 0.4 were observed. We believe that this relates to increased sensitivity associated with the ELISA test. Antibody titers as determined by ELISA for the 40 antibody positive samples were distributed as follows: 40 (11 samples), 80 (13 samples), 160 (11 samples), 320 (3 samples), and 640 (2 samples; Fig. 1
). By immunoblotting, all 40 samples were found to have antibody binding to B. abortus antigens, but not to B. canis antigens, at dilution of 1:100.
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We thank Dr. Alexander Cox for critical reading of the manuscript. This work was supported, in part, by grants from Scientific Research (16017207 and 16790250), the Japan Society for the Promotion of Science, and the Inamori Foundation.
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Received for publication 20 May 2005.
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