Trypanosoma brucei: comparison of circulating strains in an endemic and an epidemic area of a sleeping sickness focus.

Human sleeping sickness in East Africa is characterized by periods of long-term endemicity interspersed with short-term epidemics. The factors generating these huge changes are largely uncharacterized but probably reflect complex interactions among socioeconomic factors, ecological factors, and the movement and diversity of trypanosome strains. To investigate the role of trypanosome strains in the generation of these epidemics, we addressed two important questions. (1) Are the trypanosome strains circulating within a focus the same during times of endemicity and during an epidemic? (2) How stable are trypanosome strains within a single animal reservoir host? Using restriction fragment length polymorphism analysis of repetitive DNA, we have examined the relationship between Trypanosoma brucei isolates, taken from the Busoga focus of human sleeping sickness, during an endemic period (Busia, Kenya, 1993-1994) and stocks isolated during an epidemic period (Tororo, Uganda, 1988-1990). We show that similar strains, including human infective strains, are circulating in domestic cattle (the most significant animal reservoir) in both epidemic and endemic areas of the Busoga focus. Furthermore, we show the important finding that individual animals harbor the same genotype of T. brucei for a period of time and may be clonal for a given parasite strain.