Minisatellite marker analysis of Trypanosoma brucei: Reconciliation of clonal, panmictic, and epidemic population genetic structures

The African trypanosome. Trypanosoma brucei, has been shown to undergo gene tic exchange in the laboratory, but controversy exists as to the role of ge netic exchange in natural populations. Much of the analysis to date has bee n derived from isoenzyme or randomly amplified polymorphic DNA data with pa rasite material from a range of hosts and geographical locations. These mar kers fail to distinguish between the human infective (T, b. rhodesiense) an d nonhuman infective (T, b. brucei) "subspecies" so that parasites derived from hosts other than humans potentially contain both subspecies, To overco me some of the inherent problems with the use of such markers and diverse p opulations, we have analyzed a well-defined population from a discrete geog raphical location (Busoga, Uganda) using three recently described minisatel lite markers. The parasites were primarily isolated from humans and cattle with the latter isolates further characterized by their ability to resist l ysis by human serum (equivalent to human infectivity), The minisatellite ma rkers show high levels of polymorphism, and from the data obtained we concl ude that T, b. rhodesiense is genetically isolated from T, b, brucei and ca n be unambiguously identified by its multilocus genotype, Analysis of the g enotype frequencies in the separated T, b, brucei and T, b, rhodesiense pop ulations shows the former has an epidemic population structure whereas the latter is clonal, This finding suggests that the strong linkage disequilibr ium observed in previous analyses, where human and nonhuman infective trypa nosomes were not distinguished, results from the treatment of two genetical ly isolated populations as a single population.