Description of the study area
Limmu Kosa is one of the districts located in the Oromia Regional State of Ethiopia Jimma Zone. It is bordered on the South by Kersa, on the Southwest by Mana, on the West by Gomma, on the Northwest by the Didessa River which separates it from the Illubabor Zone, on the north by Limmu Sekka, on the Northeast by the Gibe River which separates it from the West Shewa Zone and the Southern Nations, Nationalities and Peoples Region, on the East by Sokoru, and on the Southeast by Tiro Afeta. The administrative center of the District is Genet. The District was located in the altitude ranging between 1200 to 3020 meters above sea level. Rivers include the Awetu and the Dembi; notable landmarks include Lake Cheleleki and the Bolo Caves .
Study design and methodologies
Total of 70 monoconical standard traps were deployed in main Didessa River and most tributaries located in four different peasant associations namely Adis limat, Burqa gudina, Gale jimate and Busase with octenol (1-oct-3-nel), acetone and three weeks old cow urine baits . All odors were placed on the ground about 30 cm upwind of the trap. The poles of traps were greased to prevent fly predators, mainly ants. Traps were allowed to stay at the site of deployment for a period of 48 h before collection. After 48 h of deployment, the catchments of each trap were sorted by fly species and then counted, identified and analyzed. The apparent density of the tsetse flies was calculated as the number of tsetse fly catch/trap/day (FTD) . Sex of all collected flies was identified by observing the posterior end of the ventral aspect of the abdomen by hand lens and stereomicroscope hence male flies were identified by enlarged hypopygium in the posterior ventral part of the abdomen which is absent in female flies.
The dissection procedure was carried out as described by the FAO Training manual for tsetse control personnel who began by removing wings and legs after wing fry analysis was performed the age of collected male flies was recorded and ovary analysis was used to determine age of female flies similarly. Then, freshly killed tsetse flies were dissected under a dissecting microscope by using 0.9% normal saline. Trypanosome infections in dissected body parts of tsetse flies (i.e. midgut, salivary gland and mouthpart or proboscis) were observed using a compound microscope at a magnification of ×40 times . Parasites detected in the midgut, salivary glands, and mouthparts (proboscis) were considered as Trypanozoon (T. brucei), those detected in the mouthparts (proboscis) and midguts were Nanomonas (T. congolense), and those found in the mouthparts (proboscis) only was considered in the group of Duttonella (T. vivax), immature infections considered when only found in the midgut. Finally, confirmation or species identification made by Giemsa stained parasite morphology smears (slides) detected by ×100 times compound microscope magnification using oil immersion [8, 13]. The Infection rate of the parasite (IR) was calculated using the following formula :
Infection rate (IR) = Number of tse tse flies infected ×100
Total number of dissected flies
Data collected from each deployed trap were coded into appropriate variables and entered in Microsoft excel, 2010 spreadsheet. All statically analyses were performed using STATA- 12 software. The Infection Rate (IR) was calculated for all data as the number of infected individuals divided by the number of individuals sampled times 100. Categorical data were analyzed by using the chi-square (c2) test of independence. In all cases, 95% of confidence intervals were used and p-value less than 0.05 were considered significant .