gondii (M4). Lambs were culled at 14, 28 and 42 days post challenge. Parasite DNA was detected at significantly (p < 0.0001) lower levels in samples from the vaccinated/challenged group (0% in heart and 5.9% in skeletal muscles), when compared to the non-vaccinated/challenged animals (75% heart, 87.9% skeletal muscle). S48 T. gondii DNA was found in muscle or lymph nodes until 42 days post infection, suggesting that par- asite DNA or tachyzoites could persist longer after immunization than previously thought. Non-vaccinated/challenged animals showed more frequent lesions in muscles and central nervous system than the vaccinated animals. These results demonstrate that vaccination of lambs with the incomplete S48 T. gondii strain, can protect against establishment of tissue cysts following challenge with a complete strain of T. gondii. Consumption of undercooked meat containing T. gondii cysts is a major route of transmission to people, therefore vaccination of food animals may improve the safety of meat for human consumption.