Induction of human serum-sensitive Trypanosoma brucei stabilates into human serum-resistant "T. rhodesiense"

When chronic Trypanosoma brucei infections of mice are treated with 20 mg/kg suramin, those trypanosomes which have escaped chemotherapy because they are residing in the brain, exhibit a higher degree of human serum resistance than the original infection. This resistance increases if the chronic infection is retreated for a second time, before the trypanosomes in the brain are tested by the blood incubation infectivity test. The transformation is not due to a selection of T. rhodesiense from a T. brucei/T. rhodesiense mixture in the original stabilates as cloned derivatives also exhibit these same characteristics. The implications of this finding are discussed.