Genetic resistance to Trypanosoma congolense infections in mice.

The mechanisms of genetic resistance or "trypanotolerance" to infection with Trypanosoma congolense were investigated in two strains of mice. One strain C57BL, is outstandingly resistant to most stabilates of T. congolense and can survive for over 80 days, whereas CFLP, in common with most other strains, generally succumbs in less than 20 days. Evaluation of several pathophysiological and immunological parameters showed that after infection both strains initially developed similar levels of parasitemia, anemia, biochemical derangement, and immunosuppression. The most outstanding difference was after day 8 postinfection, when the susceptible strain (CFLP) sustained high levels of parasitemia (10(9) trypanosomes per ml) until death 2 to 4 days later, whereas the resistant strain (C57BL) showed a marked decrease to less than 10(6) trypanosomes per ml by day 10 postinfection. Clear evidence that this was associated with the presence of trypanocidal antibody in the resistant mice was provided by the results of an infectivity neutralization test on serum collected from each strain at 10 days postinfection. Chronically infected C57BL mice showed declining waves of parasitemia and a slow restoration of most hematological and biochemical indexes to near normal levels by 80 days postinfection, although at this stage they remained immunosuppressed.