DAO 108:181-186 (2014)  -  DOI: https://doi.org/10.3354/dao02715

West Greenland harbour porpoises assayed for antibodies against Toxoplasma gondii: false positives with the direct agglutination method

Marie-Anne Blanchet1,4,*, Jacques Godfroid1,5, Eva Marie Breines1, Mads-Peter Heide-Jørgensen2, Nynne Hjort Nielsen2, Ilka Hasselmeier3, Maria Iversen2, Silje-Kristin Jensen1,6, Kjetil Åsbakk1,5 

1Norwegian School of Veterinary Science, Section of Arctic Veterinary Medicine, Stakkevollveien 23, 9010 Tromsø, Norway
2Greenland Institute of Natural Resources, Kivioq 2, 3900 Nuuk, Greenland
3University for Veterinary Medicine of Hannover, Institute for Terrestrial and Aquatic Wildlife, 25761 Büsum, Germany
4Present address: Norwegian Polar Institute, Framsentret, 9296 Tromsø, Norway
5Present address: Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, University of Tromsø, Breivika, 9037 Tromsø, Norway
6Present address: Sea Mammal Research Unit, Scottish Oceans Institute, University of St. Andrews, St. Andrews KY16 8LB, UK
*Corresponding author:

ABSTRACT: We assayed blood/tissue fluid samples from 20 harbour porpoises Phocoena phocoena from western Greenland coastal waters for antibodies against the protozoan parasite Toxoplasma gondii by the direct agglutination test (DAT). Nine individuals (45%) were interpreted to be seropositive at 1:40 dilution and 4 (20%) were seropositive up to 1:160. Samples from these individuals were assayed by an enzyme-linked immunosorbent assay (ELISA), and tissue samples of the DAT-positive animals were tested by a nested polymerase chain reaction (nPCR). Results from both methods were negative, suggesting the absence of infection in the tested animals. After chloroform clean-up, all were negative when re-assayed by DAT. We concluded that infection with T. gondii was absent in all 20 animals, despite the initially positive DAT results, and that the false positives resulted from non-specific adherence to tachyzoites in the DAT assay which could be removed by the chloroform clean-up method. Our results suggest that detecting antibodies against T. gondii using the DAT or the modified agglutination technique, particularly on samples from Arctic marine animals which often are rich in lipids, may lead to false positive results. For such samples, the use of ELISA or PCR on available tissue samples may be advocated as confirmatory tests in order to avoid false positives and overestimating seroprevalence.


KEY WORDS: Toxoplasma gondii · Phocoena phocoena · Greenland · Seroprevalence · DAT · ELISA · PCR


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Cite this article as: Blanchet MA, Godfroid J, Breines EM, Heide-Jørgensen MP and others (2014) West Greenland harbour porpoises assayed for antibodies against Toxoplasma gondii: false positives with the direct agglutination method. Dis Aquat Org 108:181-186. https://doi.org/10.3354/dao02715

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