Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/26/2005
Publication Date: 10/31/2005
Citation: Dubey, J.P., Fair, P.A., Bossart, G.D., Hill, D.E., Fayer, R., Sreekumar, C., Kwok, O.C., Thulliez, P. 2005. A comparison of four serologic tests to detect antibodies to toxoplasma gondii in naturally-exposed bottlenose dolphins (tursiops truncatus). Journal of Parasitology. 91:1074-1081.
Interpretive Summary: Infection by the single-celled parasite, Toxoplasma gondii, is common in man and animals. Humans become infected by eating undercooked meat or ingesting the resistant stage of toxoplasma (oocysts) in the environment. Scientists at the Beltsville Agricultural Research Center and the National Oceanic and Atmospheric Administration, Charleston, South Carolina, report finding of Toxoplasma antibody in 146 of 146 bottlenose dolphins beached during 2003 and 2004. Dolphins are thought to become infected with Toxoplasma by ingesting water or food contaminated with oocysts. The results suggest contamination of sea water with oocysts. These results will be of interest to public health workers, parasitologists and veterinarians.
Technical Abstract: Toxoplasma gondii infection in marine mammals is intriguing and indicative of contamination of the ocean environment and coastal waters with oocysts. In a previous study, 138 of 141(97.8 %) bottlenose dolphins (Tursiops truncatus) from coasts of Florida and California were found to have antibodies to T. gondii by the modified agglutination test (MAT). Although the MAT has been found highly sensitive and specific for T. gondii antibodies from several species of terrestrial animals, it has not yet been validated for T. gondii infections in marine mammals. Furthermore, T. gondii has yet not been isolated from dolphins. In the present study, sera from 146 (60 from 2003, and 86 from 2004) T. truncatus from the coastal areas of South Carolina and Florida were tested for antibodies to T. gondii. Sera from 2003 were tested by the MAT, indirect fluorescent antibody test (IFAT), the Sabin-Feldman dye test (DT), and an indirect hemagglutination test (IHAT). All 60 dolphins were seropositive with MAT titers of 1:20 in 3, 1:40 in 19, 1:80 in 29, 1:160 in 2, 1:1,280 in 3, 1:2,560 in 2, and 1:5,120 or higher in 2 and these results were confirmed in another laboratory. The dye test titers of these dolphins were < 1:10 in 53, 1:800 in 3, 1:1,600 in 2, and 1:3,200 in 2. The IHAT titers were < 1:64 in 52, 1:128 in 1, 1:512 in 2, and 1:2,048 in 5. The IFAT titers were < 1:20 in 3, 1:20 in 47, 1:80 in 9. All 7 DT positive dolphins had high MAT titers but 2 were negative by the IHAT. In sera from 2004 samples, MAT antibodies were found in 86 of 86 dolphins with titers of 1:25 in 29, 1:50 in 23, 1:100 in 27, 1:200 in 3, 1:1,600 in 1, and 1:3,200 in 3; these sera were not tested by other tests. Overall, MAT antibodies were found in all 146 dolphin sera tested. Because marine mammals are considered sentinel animals indicative of contamination of the coastal and marine waters by T. gondii oocysts, serologically positive infections need to be validated by detection of T. gondii organisms in tissues of seropositive animals.