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.
Highlights
Toxoplasma gondii is a cosmopolitan protozoan of the Apicomplexa phylum and the aetiological agent of toxoplasmosis
2.0 × 106sporulated oocysts were obtained from the TgCatBr71 Type BrI isolate, and 1.2 × 107oocysts were obtained from the TgCatBr60 Type BrIII isolate
Nine of the ten mice inoculated with the BrI genotype oocysts showed signs of acute toxoplasmosis between 9 and 13 days p.i., with tachyzoites detected in the lungs
Summary
Toxoplasma gondii is a cosmopolitan protozoan of the Apicomplexa phylum and the aetiological agent of toxoplasmosis. Its definitive hosts are felids [1], hundreds of animal species, ranging from birds to mammals, including humans, may act as intermediate hosts [2]. This parasite is transmitted through three main routes: [1] ingestion of oocysts eliminated in the feces of felids, which become infectious in the environment and contaminate water, soil, and food; [2] consumption of raw or undercooked meat of intermediate hosts containing viable tissue cysts with bradyzoites; and [3] congenital transmission via tachyzoites from the maternal host reaching the placenta and fetus [3]. Congenital transmission derived from primary infection is considered the most common route [6], transplacental transmission may occur after recurrence of persistent infection with reactivation of latent cysts in the maternal organism [7]
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