Control of Tsetse and Trypanosomosis in the Southern Rift Valley (Step Area): Evaluation of Deltamethrin Applications
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Date
2004-06
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Abstract
A trial aimed to evaluate the efficacy of Deltamethrin (0.4% impregnated odour-baited targets and 1% pour-on formulation applied to animals) in reducing the incidence of bovine trypanosomosis and comparing the corresponding cost-effectiveness of both strategies was conducted in two selected 10X10km Universal Transverse Mercator Grids of the Southern Tsetse Eradication Project (STEP) area in the Southern Rift Valley of Ethiopia. The Grids selected were H3 & G5 designated as study Sites I & II respectively. The trial was underway from late September, 2003 to early April, 2004. The accomplishment of the trial included baseline survey (Questionnaire, Parasitology, and entomology), intervention with insecticide (Deltamethrin 0.4%) impregnated odour-baited targets at Site I(Grid H3) and Deltamethrin 1% ‘pour-on’ application to cattle at Site II (Grid G5) and monthly monitoring of the incidence of disease and apparent density of tsetse fly. Following the deployment of 460 targets (0.4% Deltamethrin impregnated and odour-baited) at a density of 4 targets /km2 at the trial Site I, the relative abundance of tsetse fly (G. pallidipes) population declined from a pre-intervention catch of 1.35 flies/trap/day to 0.05 flies/trap/day during the final trapping time in April, 2004 with about 88.88% overall reduction achieved. The associated disease (trypanosomosis) status was monitored by monthly blood sampling from the sentinel animals established prior to the intervention and the incidence in cattle dropped from 10.75% (first monitoring) to 1.8% (last monitoring) with about 83.25%. The prevalence of the disease had also dropped to 9% (P< 0.01) as compared to the pre-intervention result of 23% and as a result, an overall reduction of 60% was achieved. The corresponding overall mean PCV (packed cell volume) record had shown an improvement from 21.8% of the pre-intervention to 25.5 % (P<0.01) after intervention. Similar assessment at Site II with Deltamethrin 1% pour-on formulation started by applying to about 409 animals at a rate of 1ml/10 kg body weight and subsequently repeated on monthly basis throughout the trial period resulted in a sharp drop of the relative abundance of tsetse fly population to nil from 0.91 flies/trap/day of the pre-intervention catch with a 94.88% (P<0.01) overall reduction achieved. The incidence of the disease also declined from 10% to 0.95% (about 90.5%). The reduction from 21% to 4.75% in the prevalence of the disease was observed to be significant (P<0.01) with a 77.4% overall drop. The associated overall mean PCV value (24.1% increased to 27.2%) had shown a gradual increase (P<0.01) until the third monitoring and maintained a stable state thereafter. The use of Deltamethrin 1% pour-on proved better efficacy based on the results obtained and conclusions made. In addition to this, cost effectiveness evaluation of the intervention component was conducted. This indicated that the routine intervention cost for Pour-on formulation offered Incremental Cost-Effectiveness Ratio (ICER) ranging from 34762.54- 102927.94 USD per unit effectiveness and the use of impregnated odour-baited targets ranging from 43184.93- 942652.00 USD per unit effectiveness for tsetse control and the associated disease (trypanosomosis) reduction. The ranges imply that reasonable variation is lacking between the cost-effectiveness of the two strategies. Though this uncertainty interval ruled out the difference between using targets and pour-on, it seemed that pour-on having lower ICER on average cost and average effectiveness assessments. The integrated application of both strategies was definitely relevant and thus recommended.
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Tsetse, Trypanosomosis, Deltamethrin