Prevalence of bovine trypanosomosis and vector density in a dry season in Gamo-Gofa and Dawuro Zones, Southern Ethiopia

Trypanosomosis remains one of the biggest constraints of livestock productivity in sub-Saharan Africa. It is of particular concern in Ethiopia where crop production is largely dependent on animal traction power. This study was conducted between November 2015 and March 2016 to estimate the prevalence of bovine trypanosomosis and vector density in Gamo-Gofa and Dawuro Zones located in Southern Ethiopia. For the entomological survey, a total of 305 NGU traps were deployed for three consecutive days at different positions in the two study areas. For parasitological study, blood samples were collected from 2402 cattle and examined for the presence of trypanosomes by the buffy coat technique (BCT). Blood samples that were positive in the BCT were further tested with Giemsa-stained thin smears for identification of Trypanosoma species. In the entomological survey, a total of 4113 flies were captured of which 1605 (39%) were tsetse flies while 2508 (61%) were other biting flies of the genus Stomoxys and Tabanus. Glossina pallidipes was the only tsetse fly identified in the study areas. The overall mean apparent density of G. pallidipes was 1.8 flies per trap per day (FTD). The overall prevalence of trypanosomosis in the study areas was 5.1% (95% CI: 4.2-6.0); however, it was significantly (p < 0.001) higher in Dawuro Zone (10%) than Gamo-Gofa (1.9%). Prevalence was also noted to be significantly (p < 0.001) higher in cattle with black coat colour and those with poor body condition. Trypanosomosis was caused mainly by Trypanosoma congolense (61.8%) and to a lesser extent by T. vivax (28.5%). Mixed infection by the two spp. was seen in 9.8% of the total positive animals. Evaluation of the mean packed cell volume (PCV) of the study animals with infection status revealed a significantly (p < 0.001) lower mean PCV in parasitaemic animals (21.5 +/- 0.46SE) than aparasitaemic ones (24.3 +/- 0.11SE). Generally, the prevalence noted in the current study is moderate. However the observation of such level of infection in a dry season suggests that the disease is still an important constraint of cattle production in the study areas. Thus, we recommend that theexisting parasite and vector control interventions need to be strengthened with special emphasis to Dawuro Zone where the prevalence was significantly higher. As the current sampling was done only once and in a dry season only, further longitudinal studies including all the seasons of the year need to be considered in the future.