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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.

Serum samples were collected over a two-year period from aborting cows and their fetuses from throughout Scotland; 465 maternal sera were examined using an immunofluorescent antibody test for IgG antibody to Neospora caninum and 547 fetal sera were examined for IgM and IgG antibody to the parasite; 355 of the maternal sera were paired with their respective fetal samples. The maternal titres ranged from 1/8 to 1/16,384, with 59 per cent (275) having titres of 1/128 or 1/256. Of the 547 fetal sera, 9.9 per cent had IgM titres equal to or greater than 1/64, 11.2 per cent had IgG titres equal to or greater than 1/64 and 15.9 per cent had IgM and/or IgG titres equal to or greater than 1/64. It is concluded that a fetal IgM or IgG titre of 1/64 or more is evidence of fetal exposure to N caninum but that the examination of maternal sera is less reliable on an individual basis, although valuable for indicating the degree of infection in a herd. Although fetal seropositivity does not necessarily provide proof that N caninum was the cause of death in a given case, the observation that 15.9 per cent of aborted fetuses had antibody to the parasite shows that vertical transmission from dam to fetus is relatively common and may be an important cause of fetal loss in cattle in Scotland.

Experimentally induced toxoplasmosis in pregnant ewes was treated with a combination of sulphamezathine and pyrimethamine. Fifteen untreated ewes gave birth to 14 live and six dead lambs whereas all the 15 lambs born to the 12 treated ewes were viable. The placental lesions were less severe, the gestation period was longer and the precolostral antibody titres to Toxoplasma gondii were lower, all significantly, for the lambs born to the treated ewes.