A study o n the epide mio logy of bovine trypanosomosis in selected sites of the new ly established rnsett le ments of A nger I. Anger II and Ke nar areas was conducted in East Woll cga Zone, Oromiya rnRegion, Western Ethiopia. T he p urpose of t be study was 0 delemli nc the prevalence of the rndisease and associating ri sk factors and est imate the appare nt d ensities and d istributions of tsetse rnand other biting n ics. It was also to generate baseli ne data thaI may ass ist in dec ision mak ing for rnplatU1 ing and implementation of the sett lement pro grammes. Retrospective study and rnquest ionnaire survey we re conducted to coll ect backgrou nd descri ptive data and cross-sectio nal rnsurvey to dctennine the preva lence and vector apparent densit ies and d istribut ions in late rainy rnand dry seasons in 200S /06. A to tal of 576 callie we re sa mp led and the bufTy coat technique was rnapplied to diagnose the trypanosome infection and 96 monoÂ· pyramidal t raps to capture the vector rnny. DifTercnces between parameters were tested for signi fi cance at probability levels of 0 .0.5 or rnless Results of the retrospective st udy and q uest iOlmaire survey indicated that bovine rntrypanos011l0sis is the major constraint to cattle product ion in the seillement areas. The curative rnand preventive doses of trypanocidal dmgs are commonly used 10 control the disease. I lo,(:,er. rnman} cattle owners have developed the pmctices of selling out their work oxen after each crop rnseason as the coping mechanism with the d isease risk to rep lace by new animals and generate rnadditional Income s frolll sa les . The entomological survey showed that only two tsetse species. rnGlossina mo"s;rans slIbmorsirons and G. rachilloides were found to exist along with other biting rnflies of the tabanid and l1luscid groups. The G. m. submorsirofl.l- was detected at a Illean appÂ·arcnl rndensity (fly trap. day) of 0.01 and G. tachilloides at 0 .3S. The overall apparent densities rn(Oy trap day) were found to be 0.36 (95% CI = 0.22 - 0.50). 1.26 (95~, CI = 0.55 - 1.97) and rn41.IS (9S% C I = 28.8 - S3.S) for tsetse, tabanids and muscid flics respectively in the study arl.!as. rnThe seasonal apparent densities were 0.40 and 0.33 (p> 0.05). 2. 18 and 0.34 (p < O.OS ), 76.0 and rn6.29 (p < 0.05) for tsetse, tabanids and musc id fly in late ra iny and dry seasons In corresponding rnorder. The fly apparent densit ies in different vegetation types were assessed but the dlffer..:n ccs rnwere not statistically significant (p > O.OS) for all ny kinds. The sex ratio for tsetse fl) was rndetennined and fewer proportion of ma le flies detected (21 /58) and (IS/47) du ring late rainy rnseason and the dry season, respectiV el y. The average age for ma le tsetse fly samp le population rnx rnwas estimated from wing fray analysis and observed to be 19 and 16 days for late rainy season rnand dry season , re spectively. The overall prevalence of bovine trypanosomosis was 8.9% (95% rnCI = 7 - II %) the seasonal infection ra te being 14 .9% (95% CI = II - 19%) and 2.8% (95% CI = rnI - 5%) with stat ist icall y signifi cant difference (p < 0 .001) be tween lat e rainy and the dry seasons rnrc specti vely. In all ca scs th e dominant trypanosome species was Tt:)'panosoma congolense rn56.8% (95% CI = -n - 71 %) followed by T. V;Va: 3 1.4 % (95% 1 1 - 470'0) . The prevalence of rntrypanosome infection in new ly introduced cattle fro m tset se free arcas was 11.4 % (95% CI = 8 -rn16%) whilst in native an im a ls 4.3% (95% Cl = 2 - 6%) with a stat isti cally signi fi cant difference rn( p < 0.01) between the two groups. The prevalence by sex was 8.4% (95% C I = 4 - 12 %) in the rnfe ma le and 9.1 % (95% CI = 6 - 12 %) in male counterpart. T he in fection ra tes in differcl1l1 age rngroups were nil, 8.0% (95% CI = 5 - 12 %) and 10.0% (95% CI = 7 - 13%) in animals of less rnthan I, I - 4 and nbovc 4 year-o ld , respectively. The differences in infecti on were not stati sti ca ll y rnsignificant (p > 0.05) betwecn scxes and age groups. Analysis of the interaction of the assumed rnrisk fac to rs indicated season and origin to be the risk fact ors (p < 0.0 I) for trypanosome inf(!ct ion rnamong the catt le popu lat ion of the sett lement areas. However. sex was not (p > 0.05) while age rnwas signified to be risky which is largely dctennined by absence or prescnce of exposure to tselse rncha ll enge. The risk of acquiring in fcction was lower in the dry season as comparcd to late rainy rnseason (OR = 0. 13. 95% CI = 0.06 - 0.28) and 3.36 times higher (OR = 3.36, 95% CI = 1.64 -rn6.88) in the new ly introduced than in the native cattle population. The mean PCV values were rn27.23% (95 % CI = 26.77 - 27.69%) and 20 .22 % (95% CI = 18 .75 - 21.68%) with statistica ll y rnsignificant difference (p < 0.001) for the non-paraslIaemic and parasitaemic animals respective ly. rnThe mean PCV ,' aille was negatively correlated (r = -0.35) wnh thc trypanosome prevalence. rnBovine u),panosol11osis is the major constraint in the newly established settlemen t areas. rnIntroduction of susceptibl e catlle populat ion to tsetse infested settlement areas wou ld resu lt in rnheavy lo sses espeCially annna ls coming from tsetse free areas bemg the high fisk group when the rnvector challenge is high. Different epid emio log ical c ircumstances appeared to exist that would rnmaintain the contact between tsetse and the hosl animal. Interiorly tsetse-infcstcd wooded bordcrs rnof many rivers and streams that lra erse the areas as well as scrap of forcst at the edge of rnsett lements to which C. /(IchillOides seems well adapted would sustain theIr constant interactIons. rnOn the other hand moderately infested peripheries to which C. m. subm orsirolls receded that have rna link with the major tsetse belt const itute a potential risk to the a reas. Furthennorc. the frequent rnx, rnmovement of ani mals coming fro m or c rossing the tsetseÂ·infestcd areas to the major market outlet rnin Uke. Kenaf prefecture is the maj or source of infected an imals. The vast potent ial land in th e rnsettlement areas would on ly be exploited if th c problcm of animal trypanoso l11 os is is resolved rnunder the present cro pÂ· li vestock farming system . Therefore, communit y based intcgratcd cOIlltro l rnoption shou ld be promoted with strong surveillance and moni toring act ivit ies