Titration of Toxoplasma gondii oocysts in non-pregnant sheep and the effects of subsequent challenge during pregnancy

Abstract

Fifty-nine ewes, seronegative to Toxoplasma gondii, were allocated to four groups which received 2000, 200, 20 or no M1 strain toxoplasma oocysts 56 days before mating. Fifty-one of them subsequently became pregnant and were challenged with 10,000 oocysts between 78 and 83 days of gestation. Infection with 2000 oocysts induced a pyrexia, seroconversion and protective immunity in all the recipient animals. Ewes that received either 20 or no oocysts before pregnancy were susceptible to subsequent challenge and severe fetal mortality occurred. In this study 200 oocysts was the threshold value for the induction of toxoplasma infection in sheep, although not all the ewes that seroconverted to this dose were protected against further challenge.

Mic1-3 KnockoutToxoplasma gondiiis a good candidate for a vaccine againstT. gondii-induced abortion in sheep

“…In three separate experiments, the Mic1-3KO tachyzoites readily infected seronegative sheep. A mild febrile reaction was observed following inoculation, a clinical sign consistent with infection of susceptible sheep with T. gondii [2, 4, 29]. Following s.c. injection of 10 5 S48 tachyzoites the febrile response was more severe and lasted longer.…”

“…Following infection, sheep develop a protective Th1-type cell mediated immunity [23] and will not normally abort due to toxoplasmosis in future pregnancies [5, 29, 35]. This suggests that a strategy based on vaccination should be successful.…”

Distribution of Lesions in Fetal Brains Following Experimental Infection of Pregnant Sheep With Toxoplasma gondii

“…Finally, the timing of the maternal serologic response to challenge in this controlled study was similar to that described in sheep in previous T. gondii challenge studies. 22,24,25 This study involved counting discrete lesions typical of T. gondii encephalitis per unit area within a 2-dimensional plane. The categorization of the 3 ''types'' of lesion enumerated in this study is somewhat arbitrary because the lesions observed in 2 dimensions were components of larger 3-dimensional phenomena; therefore, ''type'' of lesion observed depends on the plane of section.…”

Vaccination againstToxoplasma gondii: an increasing priority for collaborative research?

“…This stage of the parasite is very resistant in the environment and can survive and remain infective in moist temperate conditions for approximately 12-18 months. Experiments have shown that it only requires 200 oocysts to cause disease in sheep [14].…”