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The article provides information on a study which determined whether lesion density varies significantly among different areas of the fetal brain in experimental congenital Toxoplasma gondii infection of sheep. The study examined animal tissue samples generated as part of a larger, multidisciplinary investigation of experimental toxoplasmosis in pregnant sheep. Six ovine fetal brains were harvested 33 to 35 days post challenge from 5 ewes.

Abstract: The host–pathogen interaction is as a key feature during the formation of tissue cysts of Toxoplasma gondii within intermediate hosts. In this study, we investigated whether oral infection of lambs with T. gondii oocysts may be used as an experimental model in sheep to study this interaction, with the main objective being to detect the presence and distribution of lesions and parasite within different organs at different time points after oral infection. Lambs were infected with 5×103 and 5×105 sporulated T. gondii oocysts and culled at 2, 3, 5 and 6 weeks post-infection (WPI). During the infection, rectal temperature of the animals and serological antibodies against T. gondii were monitored. The presence of inflammatory lesions and parasite were evaluated through histological and immunohistochemical methods at different organs (brain, liver, lung, heart and lymph nodes). The lambs showed no clinical signs other than fever, and lesions appeared mainly in the brain, characterized by glial foci and perivascular cuffs, and in the heart, denoted by foci of interstitial myositis. Tissue cysts and tachyzoite-like structures were observed at all time points studied in the brain, where together with the glial foci they appeared mainly in the cerebral cortex of the forebrain and in the midbrain, but also in the heart, lung and lymph nodes. This study shows that oral infection with sporulated oocysts in lambs may provide a model for investigating the host–parasite interaction in situ during the development of tissue cysts. [Copyright &y& Elsevier]

To investigate the potential role of endogenous transplacental transmission of Toxoplasma gondii, 31 seropositive ewes presumed to be persistently infected with the parasite and 15 seronegative ewes were mated and monitored throughout pregnancy and lambing. Antibody titres were determined in precolostral sera from the liveborn lambs and in thoracic fluid from the dead lambs. A PCR for the B1 gene of T gondii was applied to the placentas from all the ewes and to the brains of the stillborn lambs. Samples of brain, lung, liver, spleen and heart from the dead lambs were examined by histopathology. No evidence of toxoplasmosis was detected by histopathology or PCR in any of the samples, but low titres of antibody to T gondii were detected in two liveborn, healthy offspring of a seropositive ewe by the immunofluorescent antibody test (3.2 per cent of pregnancies and 4.1 per cent of lambs in the seropositive group). Antibody to specific antigens of T gondii was demonstrated in sera from these two lambs by Western blotting. [ABSTRACT FROM AUTHOR]

Sheep immunized with Toxoplasma gondii (Toxovax®) prior to pregnancy were tested for their ability to withstand a challenge at 90 days gestation with 10[sup 7] 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. [ABSTRACT FROM AUTHOR]

Abstract: Toxoplasma gondii, an intracellular protozoan parasite, is one of the major causes of infectious abortion in sheep. To further understand the pathogenesis of toxoplasmosis, serum, amniotic and allantoic fluids and foetal stomach contents were collected from experimentally infected pregnant ewes to determine pathogen numbers and other markers of infection. Fifteen pregnant ewes (90 days of gestation) were each orally inoculated with 3000 sporulated oocysts of T. gondii. Serum samples were collected weekly following challenge. Amniotic and allantoic fluids and foetal stomach contents were collected at 21, 25, 28, 33 and 35 days post-infection. Characteristic placental lesions were detected in 1 of 4 challenged ewes at day 25, 3 of 4 challenged ewes at day 28 and in all challenged ewes at days 33 and 35 post-infection. T. gondii was detected only sporadically in amniotic and allantoic fluids before 35 days of infection, by real-time PCR, and only in ewes with placental lesions. At 35 days post-infection, high numbers of parasite were detected in both amniotic and allantoic fluids. An increase in the number of fluids from challenged animals with IgM and IgG was detected over time, except for IgG in allantoic fluid, which was detected in all samples from day 21 post-infection. IgG in amniotic and allantoic fluids was shown to be specific for T. gondii, and reacted with antigens with an apparent molecular mass of approximately 22kDa and 30kDa. Results suggest a maternal source of immunoglobulin in the allantoic fluid and a foetal source of immunoglobulin in the amniotic fluid early in infection but that both sources may contribute immunoglobulin to both fluids at a later stage. [Copyright &y& Elsevier]

Abstract: A real-time PCR (rt-PCR) targeting the 529-bp repeat element (RE) of Toxoplasma gondii was used to detect and quantify the parasite burden in maternal and foetal tissues in 18 seronegative ewes infected with 3000 toxoplasma oocysts on day 90 of pregnancy. The infected ewes were sacrificed in groups of 4–6 at 21, 25, 33 and 35 days post-challenge. Ten sham inoculated pregnant ewes were used as controls. T. gondii was not detected in the control ewes or their foeti. The parasite was only detected in the maternal tissues in a few of the challenged ewes on a small number of occasions where it was identified in spleen and uterine lymph nodes. T. gondii was detected in the foetal spleen and liver at the early sacrifice times but only sporadically thereafter. In the case of amniotic, allantoic and foetal aqueous humor samples T. gondii was only detected on a small number of occasions. However, it was found in the majority of the foetal lung and placentome samples throughout the study period, while placentomes and foetal brains contained high levels of the parasite during the later stages. Histopathological examination of placentome and brain tissue from the foeti in the present study revealed a strong correlation between histopathological lesions and quantities of the parasite DNA detected. These results indicate that the cotyledonary component of the foetal membranes is the sample of choice for the diagnosis of T. gondii by rt-PCR, followed by foetal lung and brain. [ABSTRACT FROM AUTHOR]