Congenital Transmission of Toxoplasma gondii After Experimental Reinfection With Brazilian Typical Strains in Chronically Infected Sheep

Toxoplasma gondii is a cause of congenital diseases, miscarriages and stillbirths in production animals. In Brazil, non-archetypal genotypes of the parasite may be related to severe disease. Experimental infection with T.gondii was studied in sheep to analyse congenital transmission-related parameters in reinfections with different Brazilian parasite strains. Thirteen T gondii-seronegative sheep were orally infected with 2 x 10(3) oocysts for the primary infection: G1 (4 animals) were inoculated with TgCatBr71 strain (Type Brl genotype) and G2 andG3 (5 and 4 animals, respectively) with TgCatBr60 strain (Type Brill genotype). After chronification of infection, the animals were impregnated. A second infection was performed after 60 days of gestation. The G1 and G3 animals were inoculated with TgCatBr606Brlll and the G2 animals with TgCatBr71 Brl oocysts. The effects of reinfection were compared with a control group (5 animals) through physical examination, ultrasound imaging and serology. Ovine experimental infections were evaluated using mouse bioassays, molecular analysis, serological tests, histopathology, and immunohistochemistry. No abortions occurred; a seropositive lamb and a mummified fetus from G2-BrlllxBrl were produced. The vertical transmission rate detected in lambs from chronically infected sheep was 31.6% (6/19). It is demonstrated that reinfection and subsequent congenital transmission occured in one sheep with a primary Brl infection challenged with Brill genotype of T gondii. In a twin pregnancy from G2-BrlllxBrl, congenital transmission from a latent infection was detected in both lambs. Congenital transmission could not be tracked in three lambs. Overall, previous T gondii infection may fail to protect against congenital transmission from a reinfection and primary infection induced insufficient protection against vertical transmission which must be taken into account in decision-making for the use of seropositive animals as breeders. Similar trials with larger groups and contemplating host cellular immune response studies should be conducted to evaluate the actual impact of T gondii reinfection involving different strains in sheep.