Studies of serological reactions in ovine toxoplasmosis encountered in intensively-bred sheep

High levels of congenital transmission of Toxoplasma gondii in a commercial sheep flock

Our current understanding of congenital transmission of Toxoplasma gondii from ewe to lamb dictates that infection frequently results in abortion and the death of the developing foetus, that the birth of live infected lambs occurs rarely and that the cat is the predominant source of infection in ewes. Using direct polymerase chain reaction detection of T. gondii, we report high levels of congenital transmission occurring in a commercially managed sheep flock. We sampled foetal-derived placental tissue and tissues from aborted lambs and showed that congenital transmission was detected in these tissues from 61% of all pregnancies. Where pregnancies resulted in the death of one or more lambs, T. gondii was detected in the lamb tissue for all but one of 18 (94%) pregnancies. Of the successful pregnancies resulting in the birth of live lambs we were able to detect T. gondii in foetal-derived placental tissue from 37 of 70 (42%) pregnancies. These results show that congenital transmission is occurring in a high percentage of lambings including normal healthy lambings, at this farm, suggesting that this route of transmission from generation to generation may be much more significant than that reported previously. These results may have implications for sheep husbandry and future epidemiological studies of T. gondii.

Serology of experimental toxoplasmosis in pregnant ewes and their foetuses

Ewes were inoculated orally with 1500 Toxoplasma gondii oocysts at 6 to 14 weeks of pregnancy. Abortions occurred at 26 to 55 days after inoculation, and maternal serum T. gondii antibody titres did not peak/plateau until 20 to 103 days after inoculation, usually after abortion occurred. Serums or body fluids from unautolysed foetuses aborted at 35 days or more after maternal inoculation, contained significant levels of Toxoplasma antibodies as determined by the indirect fluorescent-antibody test. It was considered that foetal serology was a quick and efficient method of diagnosing congenital toxoplasmosis in sheep on a flock basis.