Some aspects of the epidemiology and chemotherapy of African trypanosomiasis

Trypanosomiasis affects man and his domestic Livestock in 10 million km2 of tropical Africa. It is a major constraint to the economic development of animal production in Zambia in one third of which mixed farming is rendered impracticable. In this study an attempt has been made to investigate the epidemiology of animal trypanosomiasis in Zambia and to evaluate the efficiency of the currently used drug regime for the control of the disease. Further, the prevalence of infected domestic livestock in selected areas of the country and the efficacy of two anti-trypanosomal drugs Berenil and Samorin were investigated. It was found that the incidence of bovine trypanosomiasis is high. Trypanosoma vivax infections in one of the areas surveyed became more prevalent as distance from the tsetse-belt increased. There was an apparent increase in the incidence of T. brucei infections in cattle and five clinical cases of such infections are described. Treatment of calves with either Berenil (diminazene aceturate) or Samorin (isometamidium chloride) either 24 hours or 21 days after infection with T. vivax or T. congolense subsequently resulted in a relapsing parasitaemia. This is the first time that relapsing T. congolense and T. vivax infections following Berenil or Samorin treatment have been described in Zambia. Further investigation of the effects of Berenil on T. brucei infections in mice demonstrated that the source of relapsing infection was the brain. This finding has relevance to trypanosomiasis of domestic animals in which Berenil is a commonly used drug and also to human trypanosomiasis which, in the late stages of the disease, affects the central nervous system. The study indicated that the efficacy of current chemotherapeutic regime in Zambia should be critically examined and that more information on the incidence of animal trypanosomiasis is required.