Submitted to: Journal of Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/10/2010
Publication Date: 9/1/2010
Citation: Dubey, J.P., Chellaiah, R., Ferreira, L.R., Kwok, O.C., Sinnett, D., Majumdar, D., Su, C. 2010. A new atypical highly mouse virulent Toxoplasma gondii genotype isolated from a wild black bear in Alaska. Journal of Parasitology. 96:713-716. Interpretive Summary: Toxoplasma gondii is a single-celled parasite of all warm-blooded hosts worldwide. It causes mental retardation and loss of vision in children, and abortion in livestock. Cats are the main reservoir of T. gondii because they are the only hosts that can excrete the resistant stage (oocyst) of the parasite in the feces. Humans become infected by eating undercooked meat from infected animals and food and water contaminated with oocysts. This paper reports on new genetic type of Toxoplasma from a bear. The results will be of interest to biologists, parasitologists, public health workers, and veterinarians.
Technical Abstract: Most strains of Toxoplasma gondii isolated in North America and Europe are grouped into three (Types I, II, III) genetic types and are considered clonal. Recent evidence suggests that illness due to toxoplasmosis in immunocompetent persons may be related to infection with atypical genotype; these strains are mouse virulent. In the present study, a new mouse virulent atypical T. gondii genotype was isolated from an asymptomatic black bear (Ursus americanus) from Alaska, USA. The bear had a titer of 1:1,600 in the modified agglutination test for T. gondii. Swiss Webster out-bred mice inoculated with bear heart homogenate died of acute toxoplasmosis, 12 days p.i. Cats fed tissues from chronically infected animals (30 day infection) shed oocysts but cats fed acutely infected mice ( 12 and 18 days p.i.) did not. The isolate (designated TgBbUS1) was mouse virulent, mice inoculated with 1 oocyst died of acute toxoplasmosis. The restricted fragment length polymorphism using 10 markers revealed that the strain possessed an atypical genotype; type I allele at loci SAG1, (5’-3’)SAG2, SAG3, c22-8, c29-2, L358, and Apico, type II allele at locus alt.SAG2, and type III allele at loci BTUB, GRA6, and PK1. DNA sequencing at intron loci EF1, HP2 and UPRT1 revealed that the TgBbUS1 is a divergent T. gondii strain. These results indicate that mouse virulent atypical T. gondii genotypes are also circulating in wildlife in the US.