A Study of the Prevalence of Bovine Trypanosomosis and Trypanocidal Drug Resistance in Coastal Tanzania

Abstract

Although bovine trypanosomosis and trypanocidal drug resistance have been well documented at some sites in Tanzania, notably Mkwaja Ranch, there is little detailed information on the extent of the problem on an area-wide basis. A survey was conducted between May 1997 and December 1998 in 30 sampling sites in Tanga, Coast and Dar es Salaam Regions of Tanzania. Samples (n = 2761) from cattle over 6 months of age were collected. Buffy-coats were examined for presence/absence of trypanosomes using the haematocrit centrifugation buffy­coat technique and Giemsa-stained blood films. Blood was collected for preparation of trypanosome stabilates for drug sensitivity testing, and for preparation of sera for trypanocidal drug determination. Trypanosome infections were found in cattle in 18 (60.0%) of the sampling sites. Prevalence at individual sampling sites varied between 0 and 43.0%. Overall mean prevalence was 13.0%, and 73.0% of the infections were Trypanosoma congolense, 23% T. vivax and 4% T. brucei. The highest prevalences were found at sampling sites in Tanga Region and one site (Bunju) in Coast Region (mean 14.3%). Other sites in Coast and Dar es Salaam Regions had relatively lower prevalences (mean 1.7°/o). Seventeen pools of up to 5 stabilates perpool (from a single site), of T.congolense from six sites (5 in Tanga Region and Bunju) were tested for sensitivity to isometamidium chloride (ISMM) and diminazene aceturate (DA) in mice. Using discriminatory doses of 1.0 mg/kg b.wt. ISMM and 20 mg/kg b.wt. DA, only 1 (5.9%) pool was sensitive to both drugs, 5 (29.4%) were resistant to ISMM only, none was resistant to DA only, and 11 (64.7%) were resistant to both drugs. These results indicate the presence of resistance to ISMM at two sites, and resistance to both ISMM and DA at four of the sites. Analysis of sera using isometamidium-ELISA showed wide variation in usage rates,  and further evidence  of isometamidium resistance; 18.4% of 359 trypanosome-infected cattle showed evidence of recent isometamidium treatment