Epidemiological Study of Toxoplasma gondii Infection in Ovine Breeding

An outbreak of toxoplasmosis occurring in a typical farm of 524 ovines was monitored for 1 year after the occurrence of 31 abortions. Abortion events involved 7.2% of 430 pregnant sheep. Presence of antibodies to Toxoplasma gondii in sheep sera was investigated by the indirect fluorescence antibody test (IFAT). A total of 422 ewes were bled four times during the year, and an epidemiological analysis was performed on all serology data collected in this subgroup. The prevalence of IgG positives ranged from 31.52% (133/422) at the first sampling to 62.56% (264/422) at the fourth sampling. Incidence of IgG antibodies was 38.75% at the second sampling, 14.92% at the third and 29.28% at the fourth sampling. At the beginning of the study, prevalence was 70.7% in primiparous sheep and 20.9% in sheep older than 5 years; at the third sampling, prevalence was stable at 70% in pluriparous sheep. The mean prevalence of IgM antibodies was 14.87%. A total of 147 out of all 524 ovines of the flock tested positive for IgM in more than one sampling. After an initial positivity, 60 sheep tested negative for IgG at the following serological controls (4 between the first and the second sampling, 30 between the second and the third and 28 between the third and the fourth sampling). One stray cat was positive for IgG, with a titre of 1 : 320. Moreover, one of the farmers was also positive, with a titre of 1 : 160 for IgG. A positive PCR result for T. gondii DNA was also observed in aliquots of grain and pellets taken from feed stocks amassed inside the sheds without protection, suggesting that an adequate management of the farm might be useful, if not essential, for controlling T. gondii outbreaks in ovine flocks.