Submitted to: International Journal for Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/3/2007
Publication Date: 6/1/2008
Citation: Dubey, J.P., Sundar, N., Hill, D.E., Velmurugan, G.V., Bandini, L.A., Kwok, O.C., Su, C. 2008. Toxoplasma gondii infection in lambs: high prevalence of live parasites, and genetic characterisation of T. gondii isolates revealed new genotypes. International Journal for Parasitology. 38:999-1006. 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. Toxoplasmosis causes mortality in many species of animals in the zoos, especially primates. Scientists at the Beltsville Agricultural Research Center and University of Tennessee report characteristics of Toxoplasma isolates from lambs from Maryland and Virginia. The results will be of interest to biologists, parasitologists, and veterinarians
Technical Abstract: Little information is available on the presence of viable Toxoplasma gondii in tissues of lambs worldwide. The prevalence of T. gondii was determined in 383 lambs (< 1 year old) from Maryland, Virginia, and West Virginia. Hearts of 383 lambs were obtained from a slaughter house on the day of killing. Blood removed from each heart was tested for antibodies to T. gondii by using the modified agglutination test (MAT). Sera were first screened using 1:25, 1:50, 1: 100, and 1:200 serum dilutions and hearts selected for bioassay for T. gondii. Antibodies (MAT, 1:25 or higher) to T. gondii were found in 104 (27.1%) of 383 lambs. Hearts of 68 seropositive lambs were used for isolation of viable T. gondii by bioassay in cats, mice or both. For bioassay in cats, the entire myocardium or 500 g were chopped and fed to cats, one cat per heart and faeces of the recipient cats were examined for shedding of T. gondii oocysts. For bioassay in mice, myocardium was digested in an acid pepsin solution and the digest inoculated in to mice; the recipient mice were examined for T. gondii infection. In total, 53 isolates of T. gondii were obtained from 68 seropositive lambs. Genotyping of the 53 T. gondii isolates using 10 PCR-RFLP markers (SAG1, SAG2, SAG3, BTUB,GRA6, c22-8, c29-2, L358, PK1, and Apico) revealed –genotypes; eight isolates were clonal Type II at all 10 loci, eight isolates differed from Type II at the Apico locus, 10 isolates differed from clonal Type II at two loci (L358, and Apico) and the remainder 28 isolates had a combination of I, II, or III Types; there was no clonal Type III or Type I. Results indicate a high prevalence of T. gondii in lambs, and a higher genetic diversity among ovine isolates for the first time. To minimize T. gondii transmission, lamb meat should be cooked thoroughly before human consumption, especially by pregnant women.