Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 2, 2003
Publication Date: December 13, 2003
Citation: Gajadhar, A.A., Measures, L., Forbes, L.B., Kapel, C., Dubey, J.P. 2003. Experimental Toxoplasma gondii infection in grey seals (Halichoerus grypus). Journal of Parasitology. 90:255-259.
Interpretive Summary: Infection by the single-celled parasite Toxoplasma gondii can cause abortions in livestock and birth defects in humans. Ingestion of uncooked meat is one of the important means of transmission of the parasite to humans. Scientists at the Beltsville Agricultural Research Center and the Canadian Food Inspection Service have found that T. gondii can infect and survive in seal meat for months. Therefore, all meat should be cooked thoroughly before human consumption. These results will be of interest to marine biologists, parasitologists and public health workers.
Laboratory-reared animals were used to assess the susceptibility of seals (Halichoerus grypus) to Toxoplasma gondii infection. Each of 4 seals was orally inoculated with 100 or 10,000 oocysts of T. gondii (VEG strain), and another 4 seals served as negative controls. Occasionally, mild behavioral changes were observed in all inoculated seals, but not in control animals. A modified agglutination test revealed the presence of antibodies to T. gondii in sera collected from inoculated seals and mice inoculated as controls. No evidence of the parasite was found on an extensive histological examination of seal tissues, and immunohistochemical staining of tissue sections from inoculated seals revealed a single tissue cyst in only 1 seal. Control mice inoculated with 10 oocysts from the same inoculum given to seals became serologically and histologically positive for T. gondii. Cats that were fed brain or muscle tissue collected from inoculated seals passed T. gondii oocysts. This study demonstrates that T. gondii oocysts can establish viable infection in seals, and supports the hypothesis that toxoplasmosis in marine mammals can be acquired from oocysts in surface water runoff and sewer discharge.