dc.description.abstract | In an on-farm trial conducted amongst the Maasai pastoralists in Nkuruman and Nkineji areas of Kenya between April 2004 and
August 2005 designed to evaluate the effectiveness of a synthetic tsetse repellent technology, we assessed the relationship between
tsetse challenge and trypanosomosis incidence in cattle. Six villages were used in each area. Each of these villages had a sentinel
cattle herd that was screened for trypanosomosis on monthly basis using buffy coat technique. Animals found infected at each
sampling were treated with diminazene aceturate at 7 mg kg 1 body weight. Treatments administered by the owners over the
sampling intervals were recorded as well. Tsetse flies were trapped at the time of sampling using baited stationary traps and apparent
tsetse density estimated as flies per trap per day (FTD). A fixed proportion (10%) of the flies was dissected and their infection status
determined through microscopy. Blood meals were also collected from some of the flies and their sources identified using enzymelinked
immunosorbent assay (ELISA). Tsetse challenge was obtained as a product of tsetse density, trypanosome prevalence and the
proportion of blood meals obtained from cattle. This variable was transformed using logarithmic function and fitted as an
independent factor in a Poisson model that had trypanosomosis incidence in the sentinel cattle as the outcome of interest. The mean
trypanosomosis incidence in the sentinel group of cattle was 7.2 and 10.2% in Nkuruman and Nkineji, respectively. Glossina
pallidipes was the most prevalent tsetse species in Nkuruman while G. swynnertoni was prevalent in Nkineji. The proportions of
tsetse that had mature infections in the respective areas were 0.6 and 4.2%. Most tsetse (28%) sampled in Nkuruman had blood
meals from warthogs while most of those sampled in Nkineji (30%) had blood meals from cattle. A statistically significant
association between tsetse challenge and trypanosomosis incidence was obtained only in Nkuruman when data was pooled and
analyzed at the area but not at the village-level. In the later scenario, lagging tsetse challenge by 1 month improved the strength but
not the significance of the association. These findings show that when the spatial unit of analysis in observational studies or on-farm
trials is small, for instance a village, it may not be possible to demonstrate a statistically significant association between tsetse
challenge and trypanosomosis incidence in livestock so as to effectively control for tsetse challenge. | en |