A previous infection withToxoplasma gondiidoes not protect against a challenge withNeospora caninumin pregnant sheep

Abstract

Sheep immunized with Toxoplasma gondii (Toxovax) prior to pregnancy were tested for their ability to withstand a challenge at 90 days gestation with 107 Neospora caninum (NC1) tachyzoites. The antibody responses in sheep following immunization with T. gondii were specific for T. gondii whereas peripheral blood mononuclear cells responded to both T. gondii and N. caninum antigen in vitro. This suggested that there was induction of crossreactive immune recognition in the sheep, at least at the cellular level. Following challenge of sheep at mid-gestation with N. caninum, no febrile responses were recorded in the group of sheep which had previously received Toxovax while significant febrile responses were recorded in the group of sheep which received N. caninum challenge alone. Antibody responses to N. caninum developed in all sheep following N. caninum challenge and antibody responses to T. gondii were boosted in the group of sheep which had previously been immunized with Toxovax. No antibodies to T. gondii were observed in the sheep which received the N. caninum challenge alone. Peripheral blood mononuclear cells from both groups of sheep responded to T. gondii and N. caninum antigen in vitro and interferon gamma was present in the cell-free supernatant from activated cells. However despite evidence of the induction of crossreactive immunity between T. gondii and N. caninum, this was not sufficient to prevent foetal death. The group of sheep which had received Toxovax prior to pregnancy and the group of sheep which only received the N. caninum challenge experienced 100% foetal death compared with 0% in the unchallenged control group. Vaccination prior to pregnancy with Toxovax did protect against foetal death following oral challenge at 90 days with 2000 T. gondii oocysts which caused 100% foetal death in a control challenge group.

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

“…Since T. gondii protective immunity in sheep involves cellular responses [23, 25], diluted whole blood samples collected three weeks after s.c. inoculation with 10 5 or 2 × 10 6 Mic1-3KO tachyzoites (Exp. 2), were exposed to T. gondii antigen in vitro (data not shown).…”

The prevalence ofNeospora caninumand co-infection withToxoplasma gondiiby PCR analysis in naturally occurring mammal populations

“…Previous in vitro studies (Sunderman and Estridge, 1999) have demonstrated that Toxoplasma and Neospora can co-exist in tissue culture, and both species could invade the same host cell and undergo endodyogeny. Immunological studies (Innes et al 2001) showed that, although there was evidence of induction of cross-reactive immune recognition following immunization with T. gondii in sheep, this was not sufficient to prevent foetal loss following subsequent N. caninum oocyst challenge.…”

Protection against LethalNeospora caninumInfection in Mice Induced by Heterologous Vaccination with amic1 mic3KnockoutToxoplasma gondiiStrain

“…In this study, we have demonstrated that heterologous immunization with an attenuated T. gondii strain induced protec- Previous studies have provided evidence of humoral and cellular cross-reactivity between T. gondii and N. caninum in different hosts (16,19,21,32), but the extent to which T. gondii immunization could protect against subsequent N. caninum infection has never before been investigated using the mouse model. Whereas in a pregnant-ruminant model of N. caninum infection, a T. gondii vaccinal strain failed to induce protection against N. caninum-induced abortion (16), mice infected with N. caninum were protected against lethal toxoplasmosis (19).…”

“…The heterologous protection induced by a commercial strain of T. gondii was previously studied by Innes et al using a ruminant model for congenital infection with N. caninum. This vaccination failed to protect against an N. caninum challenge at 90 days of gestation (16). The authors discuss the fact that under their challenge conditions, the immunity generated against the antigens common between T. gondii and N. caninum was insufficient to protect against fetal death, but if their challenge had been milder, it might allow detection of a biological effect.…”