Submitted to: International Journal for Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/20/2001
Publication Date: N/A
Citation: Interpretive Summary: Infection by the single celled parasite Toxoplasma gondii are common in humans and livestock. It causes mental retardation and loss of vision in children and abortion in livestock. Humans become infected by eating uncooked infected meat or by ingesting food and water contaminated with oocysts shed in feces of infected cats. Scientists at the Beltsville Agricultural Research Center and University of Sao Paulo, Brazil, have isolated virulent strains of Toxoplasma from tissues of backyard chickens for the first time. These findings will be of interest to biologists, parasitologists and public health workers.
Technical Abstract: In spite of a wide host range and a world wide distribution, Toxoplasma gondii has a low genetic diversity. Most isolates of T. gondii can be grouped into 3 lineages, types I, II, and III. Type I stains are considered highly virulent in outbred laboratory mice, and have been isolated predominantly from clinical cases of human toxoplasmosis whereas types II and III strains are considered a virulent for mice. In the present study, 17 of 25 of the T. gondii isolates obtained from asymptomatic chickens from rural areas surrounding Sao Paulo, Brazil were type I. Antibodies to T. gondii were measured in 82 chicken sera by the modified agglutination test using whole formalin-preserved tachyzoites and mercaptoethanol. Antibodies to T. gondii (MAT 1:10 or more) were found in 32 chickens. Twenty-two isolates of T. gondii were obtained by bioassay in mice inoculated with brains and hearts of 29 seropositive (>1:40) chickens and 3 isolates were obtained in the feces of cats fed tissues from 52 chickens with no or low levels (<1:40) of MAT antibodies. In total, 25 isolates of T. gondii were obtained by bioassay of 82 chicken tissues into mice and cats. All type I isolates killed infected mice within 4 weeks whereas type III isolates were less virulent to mice. There were no type II isolates. This is the first report of isolation of predominantly type I strains of T. gondii from a food animal. Epidemiological implications of these findings are discussed.