Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2004
Publication Date: May 1, 2004
Citation: Lindsay, D.S., Collins, M.V., Mitchell, S.M., Wetch, C.N., Rosypal, A.C., Flick, G.J., Zajac, A.M., Lindquist, A., Dubey, J.P. 2004. Survival of Toxoplasma gondii oocysts in eastern oysters (Crassostrea virginica). Journal of Parasitology. 90(5):1054-1057.
Interpretive Summary: Infections by the single-celled parasite Toxoplasma gondii causes mortalities in humans and animals. Recently, Toxoplasma has been found to kill marine mammals. Scientists at the Beltsville Agricultural research Center and Virginia Tech, Blacksburg, have found that Toxoplasma oocysts can survive in sea water for six months. These findings will be of interest to biologists, parasitologists and public health workers.
Toxoplasma gondii has recently been recognized to be widely prevalent in the marine environment. It has previously been determined that Eastern oysters (Crassostrea virginica) can remove sporulated T. gondii oocysts from seawater and that oocysts retain their infectivity for mice. The present study examined the long-term survival of T. gondii oocysts in oysters and examined how efficient oysters were at removing oocysts from seawater. Oysters in 76-L aquaria (15 oysters per aquarium) were exposed to 1 x 106 oocysts for 24 hr and examined at intervals up to 85 days post-exposure (PE). Ninety-percent (9 of 10) of these oysters were positive day 1 PE using mouse bioassay. Tissue cysts were seen in 1 of 2 mice fed oyster tissue from oysters exposed 21 days previously. Toxoplasma gondii antibodies were found in 2 of 3 mice fed oysters that had been exposed 85 days previously. In an other study, groups of 10 oysters in 76-L aquaria were exposed to 1 x 105, 5 x 104, or 1 x 104 sporulated T. gondii oocysts for 24 hr and then processed for bioassay in mice. All oysters exposed to 1 x 105 oocysts were infected and 60% of oysters exposed to 5 x 104 oocysts were positive when fed to mice. The studies with exposure to 1 x 104 oocysts were repeated twice and 10% and 25% of oysters were positive when fed to mice. These studies indicate that T. gondii can survive for several mo in oysters and that oysters can readily remove T. gondii oocysts from seawater. Infected filter feeders may serve as a source of T. gondii for marine mammals and possibly humans.