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

Abstract

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 × 10³oocysts for the primary infection: G1 (4 animals) were inoculated with TgCatBr71 strain (Type BrI genotype) and G2 andG3 (5 and 4 animals, respectively) withTgCatBr60 strain (Type BrIII genotype). After chronification of infection, the animals were impregnated. A second infection was performed after 60 days of gestation. TheG1 andG3 animals were inoculated withTgCatBr60BrIII and the G2 animals withTgCatBr71 BrI 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-BrIIIxBrI 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 BrIII genotype of T. gondii. In a twin pregnancy from G2-BrIIIxBrI, 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.

Keywords: abortion; oocysts; ovine; toxoplasmosis; vertical transmission.

Figure 1

Sheep rectal temperatures after experimental prime infection using oocysts of Toxoplamsa gondii isolates TgCatBr71 (genotype BrI or TOXODB#6) and TgCatBr60 (genotype BrIII or TOXODB#8) ^*low and high limits of normal temperatures.

Figure 2

Curves of average anti-Toxoplasma gondii antibody titres from sheep after experimental prime infection using oocysts of the isolates TgCatBr71 (genotype BrI or TOXODB#6) and TgCatBr60 (genotype BrIII or TOXODB#8) followed by a second experimental infection during pregnancy (arrow) using oocysts from the same or from a different genotype, showing statistical significance (^*) on group 1 (BrI x BrIII).

Figure 3

Toxoplasma gondii specific labeling by immunohistochemistry in tissues of congenitally infected lambs. (A) Lymph node from lamb 1 of sheep 1 from G1, 100x; (B) Lymph node from lamb 1 of sheep 7 from G2, 100x; (C) Brain from lamb of sheep 9 from G2, 100x; (D) Lymph node from lamb of sheep 9 from G2, 100x; (E) Brain from lamb of sheep 10 from G3, 100x; (F) Lymph node from lamb of sheep 10 from G3, 40x; (G) Heart from lamb of sheep 10 from G3, 100x; (H) Lymph node from lamb 1 of sheep 11 from G3, 100x.