The use of molecular biological tools to investigate transmission routes and epidemiology of Toxoplasma gondii

Toxoplasma gondii is a major cause of abortion in humans and livestock. This work focuses on three main areas. Firstly, an investigation of congenital transmission of T. gondii in sheep. Using SAG1 PCR as a detection system, high levels of congenital transmission were shown in two sheep flocks (69% of commercial sheep pregnancies and 60% of Charollais sheep pregnancies). Furthermore, this occurred longitudinally over several lambings indicating that this route of transmission is more important than previously anticipated. Reproductive losses were investigated by analysis of stock records and these levels (8.2% of commercial flock lambs and 18.9% of pedigree Charollais flock lambs) were comparable to the national average. Congenital transmission was determined by PCR detection of parasite DNA in lamb cords and aborted tissues.The second part of the thesis describes the study of T. gondii infection in urban mice. PCR was used to detect the parasite, and 59% of the 200 mice caught were infected. Congenital transmission rates were determined by testing foetal tissue of pregnant females. All pregnant and infected females had transmitted the parasite to at least one of their offspring, resulting in a frequency of transmission of 100%, with an overall rate of transmission to 60.2% of pups. Population genetic analyses of mice (carried out by microsatellite sequence analysis) indicated that each block sub-population represents a separate breeding unit. Infection rates did not vary significantly between these groups