Effects of changing climate and vegetation on Trypanosomosis burden in the Gambia

Abstract

The aim of this one year long longitudinal study was to update the current prevalence of trypanosomosis in cattle, tsetse density and challenge that could have been influenced by changes in climatic factors and land use.

A total of 3651 cattle blood samples were collected from 120 randomly selected cattle herds in both Kiang West and Niamina East Districts of The Gambia during six bimonthly sampling in 2011. The blood samples were examined using the dark ground buffy coat technique to establish the cattle trypanosomosis prevalence at both herd and animal levels. During the same period, a total of 317 biconical traps were set up and harvested for two consecutive days to calculate the tsetse density and challenge. Land cover/use map for the two study sites were compared with past reports to assess the changing vegetation cover. Records on rainfall, temperature and humidity were used to assess their trends over the past three decades. All data were analysed using linear regression, logistic regression, poisson and negative binominal regression models in STATA 11 and scatter plot graphs in MS Excel.

Results of the survey on tsetse abundance and trypanosomosis prevalence shows overall tsetse density (TTD), tsetse challenge, trypanosomosis prevalence animal level and herd level of 2.0, 13.9, 3.1% and 53% in Kiang West; 2.5, 16.5, 3.2% and 55% in Niamina East, respectively. The bimonthly TTD, tsetse challenge, trypanosomosis prevalence animal level and herd level at the study sites varied as follows: 0.05-10.15 TTD, 0.00-87.63 tsetse challenge, 1.0-5.9% trypanosomosis prevalence animal level and 20-100% trypanosomosis prevalence herd level. Comparing these values with published findings, it appears that trypanosomosis prevalence and TTD in Kiang West remains the same but the tsetse challenge has increased; whilst in Niamina East the trypanosomosis prevalence remain the same but both TTD and tsetse challenge are decreasing. The assessed climatic factors showed a significant increase during the past three decades, and the habitats of tsetse flies appear to have reduced.

It is concluded that the study areas have African Animal Trypanosomosis (AAT) problem ranking of Low to Medium with some hotspots of High to Very Severe tsetse burden. Recommendations for Farmers, PROGEBE and Policy makers include strategic cattle feeding, tsetse fly control, treatment of infected animals, capacity building and recruitment of additional livestock technicians.

Keywords: trypanosomosis, tsetse density, tsetse challenge, climate changes, The Gambia