Parasite loads. At seven weeks post-infection, the number of viable parasites was determined from footpad, draining lymph nodes, and spleen of mice pre-immunized with SGH of F2, F3, F4, F5, F6, F14, and control groups. The parasite burdens in the infected tissues were assessed by limiting dilution, as described in Material and Methods. Presented values are the mean +S.D. of three mice per category.