Control of Tsetse and Trypanosomosis in the Southern Rift Valley (Step Area): Evaluation of Deltalmethrin Application
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Date
2004-06
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Publisher
AAU
Abstract
A trial aimed to evaluate the efficacy of Deltamcthrin (0.4% impregnated odour-baited
targets and I % pour-on formulation app lied to animals) in reducing the incidence of bovine
trypanosornosis and comparing the corresponding cost-effectiveness of both strategies was
conducted in two selected IOXIOkm Universal Transverse Mercator Grids of the Southern
Tsetse Eradication Project (STEP) area in the Southern Rifl Valley of Ethiopia. The Grids
selected were I-B & G5 designated as study Sites I & Il respectively. The tTial 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
(Dcltamethrin 0.4%) impregnated odour-baited targets at Site I(Grid H3) and Deltamethrin
I % 'pour-on' application to cattle at Site II (Grid G5) and monthly monitoring of the
incidence 0 f disease a nd apparent density of tsetse fly. Following the deployment 0 f 460
targets (0.4% Deltamethrin impregnated and odour-baited) at a density of 4 targets fkm2 at
the trial Site I, the relative abundance of tsetse fly (G. pal/idipes) population declined from a
pre-intervention catch of 1.35 flies/trap/day to 0.05 flie s/trap/day during t he final trapping
time in April, 2004 with about 88.88% overall reduction achieved. The associated disease
(uypanosomosis) 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 pev
(packed cell volume) record had sho\\'T1 an improvement from 21.8% of the pre-intervention
to 25.5 % (P<O.OI) after intervention. Similar assessment at Site II with Deltamethrin 1%
pour-on fonnulation started by applying to about 409 animals at a rate of ImUIO 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<O.OI) 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<O.Ol) with a 77.4%
overall drop. The associated overall mean pev value (24.1% increased to 27.2%) had
shown a gradual increase (P<O.O 1) until the third monitoring and main tained a stable state
thereafter. The usc of Deltamethrin I % pour-on proved better efficacy based on the results
obtained and conclusions made.
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In addition to this, cost effectiveness evaluation of the intervention component was
conducted. This indicated that the routine intervention cost for Pour·on fonnulation offered
Incremental Cost· Effectiveness Ratio (leER) 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 c ost·cffcctiveness 0 r the two strategies. Though t his uncertainty interval ruled out the
difference between using targets and pour·on, it seemed that pour·on having lower leER on
average cost and average effectiveness assessments. The integrated application of both
strategies was definitely relevant and thus recommended.
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Keywords
Tsetse; Trypanosomosis; Deltamethrin; efficacy; intervention; cost•effectiveness; sentinel cattle; pour•on; targets