Enzyme variation in Trypanosoma brucei spp. I. Evidence for the sub-speciation of Trypanosoma brucei gambiense.

Three groups of stocks of Trypanosoma brucei ssp, defined by the criteria of host, human serum resistance and place of isolation as T. b. gambiense, T. b. brucei (Nigeria) and T. b. brucei/rhodesiense (non-gambiense, Uganda) were screened for electrophoretic variation at 20 enzyme loci. One enzyme (Peptidase C) was found to differentiate all T. b. gambiense stocks from the other T. brucei stocks and, taken together with specific variants of 5 other enzymes, could be used to unambiguously define T. b. gambiense stocks. Using a population genetics approach, the frequencies of the different variants in the three groups of stocks were estimated and from them the average similarity and difference between groups were measured using the statistics of genetic identity (I) and genetic distance (D). These results show firstly, that T. b. gambiense is more different from the other two groups than they are from each other and, secondly, that the values of I and D obtained are consistent with T. b. gambiense constituting a sub- or sibling species of T. brucei. Three domestic animal isolates from Zaire and Cameroun were also screened for enzyme variation and two of these identified as T. b. gambiense, thereby establishing the existence of an animal reservoir host. In parallel, these stocks were tested for human serum resistance resulting in the same identification. Studies of the antigen repertoires and antigen gene structure were carried out by other workers on all the T. b. gambiense stocks reported here and the same conclusions reached as to the identification and ability to discriminate this subspecies from other groups of T. brucei stocks. The results presented here are discussed in relation to other published data on enzyme variation in T. brucei.