A field evaluation of three trypanosomosis control strategies, in KwaZulu-Natal, South Africa

Abstract

Rural subsistence farming practices are the primary agricultural activity in northeastern KwaZulu-Natal, South Africa. Cattle in this area have long been affected by tsetse-borne trypanosome infections. The causative organism, Trypanosoma brucei brucei was first identified by Bruce in the late 1800’s. Approximately 120000 cattle fall within a tsetse (Glossina austeni and Glossina brevipalpis) belt common to Mozambique and South Africa. Between 1991 and 1994 cattle in this area were treated with homidium bromide, and dipped with cyhalothrin, in an attempt to control trypanosomosis. No control measures have been implemented since 1994, however, and trypanosomosis re-emerged as a threat to animal health. In order to determine the optimum control measure available, a longitudinal incidence study was conducted to evaluate three possible control options. Four sentinel herds were selected from populations exposed to similar trypanosome challenges. The baseline trypanosome incidence rate was determined for each herd, after which each herd was subjected to a different trypanosome control measure. Two of the herds were subjected to topical pyrethroid treatment (Cyfluthrin pour-on and Flumethrin plunge-dip) as vector-control measures, one herd was treated 6 weekly with an injectable trypanocidal drug (isometamidium hydrochloride), and one herd served as an untreated control group. Monthly incidence rates were determined using the ‘dark-ground buffy smear technique’. The monthly incidence rates were standardized in order to account for variation in trypanosomosis challenge between the 4 herds. The standardized rates were then compared and the impact of the control strategies was quantified using the Area Under The Curve method. The cost efficacy of each control strategy was evaluated based on a partial budget system. Both the cyfluthrin pour-on and the injectable trypanocide were cost effective and had a dramatic trypanosomosis control effect with the pour-on having the greater impact/ control. The flumethrin plunge-dip displayed moderate trypanosomosis control properties, but proved not to be cost effective.