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Toxoplasma gondii infects sheep horizontally (from cat faeces) or vertically (transplacentally). Vertically infected lambs sometimes die. Here, transmission and performance impacts were considered in one Charollais flock and one Swaledale flock. B1-PCR was performed on umbilical cord, heart and brain. MAT was performed on blood and pleural effusion. IgG-ELISA was performed on colostrum. B1-PCR was more sensitive than four other methods, producing a band in 50% of replicates when each replicate contained 0.02 parasite genome copies. 16/243 (6.6%) viable Charollais, 30/263 (11.4%) viable Swaledale, 3/54 non-viable Charollais and 0116 non-viable Swaledale were PCR-positive, showing no difference between flocks. At age four months 64/524 (12.2%) Charollais and 10/329 (3.0%) Swaledale were seropositive, showing relatively high seroprevalence in Charollais. 5/44 non-viable Charollais and 1114 non-viable Swaledale were seropositive. Colostrum ELISA was 75% sensitive and 100% specific relative to serum MAT. 15/408 (3.7%) Charollais and 31139 (2.2%) Swaledale were colostrum ELISA-positive, showing no difference between flocks. PCR positivity was not associated with seropositivity. PCR positivity was randomly dispersed between litters. In Charollais seropositivity was overdispersed between litters, seroprevalence was higher than PCR prevalence, young ewes' lambs were frequently PCR-positive and large litters frequently contained seropositive lambs. Those results might have been due to vertical transmission. In Swaledale, PCR positivity was not associated with ewe age and seropositivity was rare. Those results suggested little transmission. Lamb seroconversion, and colostrum ELISA positivity, were not associated with ewe age. Overall, it is suggested that ewes ingested oocysts but vertical transmission was sometimes interupted by lambing, especially in Swaledale. In eight cases clinical toxoplasmosis was suspected. No evidence was found suggesting subclinical effects of T. gondii leading to reduced lamb survival. Charollais born PCR-positive were relatively light at age two months but that association was not found in Swaledale. Serology did not confirm any stunting effect. |
