This study evaluates the influence of immunization with the incomplete S48 strain of Toxoplasma gondii on parasite dissemination in lambs following a live oral challenge with a complete strain of T. gondii (M4) lambs. Lambs were culled at 14, 28 and 42 days post challenge. Parasite DNA was detected at significantly lower levels in brain, heart, skeletal muscle and viscera 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 parasite DNA or tachyzoites could persist longer after immunization than previously thought. While non-vaccinated/challenged animals showed lesions in muscles and central nervous system, these were much less frequent in the vaccinated animals. These results demonstrate that vaccination of lambs with the S48 attenuated T. gondii strain, can reduce the establishment/dissemination of the challenging parasite, resulting in potentially safer meat for human consumption.