Trypanosomosis and phenotypic features of four indigenous cattle breeds in an Ethiopian field study

We conducted a two-part study in the native home areas of four cattle breeds, Abigar, Gurage, Horro and Sheko, in south-western Ethiopia. The first part of the study investigated livestock keeper knowledge about trypanosomosis and trypanotolerance. For each breed 60 livestock keepers were interviewed, resulting in a total of 240 interviews. The second part of the study focused on biological evidence for trypanotolerance. Blood samples of about 100 head of cattle per breed were collected during peak trypanosomosis challenge period and analyzed for packed cell volume (PCV) and parasitaemia. In addition individual body measurements of the sampled animals were taken and the keepers provided some information regarding their animals. Livestock keeper interviews revealed that trypanosomosis was considered a major problem in all areas (95-100%). Almost all Abigar livestock keepers knew how trypanosomosis is transmitted, whereas only 34-52% of the keepers of the other breeds had that knowledge. Most Sheko keepers (75%) knew of trypanotolerance and claimed to have trypanotolerant animals in their own herds. Among the other three breeds the knowledge of trypanotolerance was much less (8-18%). A majority of the keepers were interested in purchasing trypanotolerant animals. PCV was highest among Horro (26.2) and Sheko (25.1) cattle whereas Abigar had the lowest PCV (20.0). Sheko were least infected by trypanosomes (6%) and had the lowest number of trypanocidal treatments per year (1 treatment/animal and year). Abigar cattle were most infected (23%) followed by Gurage (20%) and Horro (17%). Gurage had by far the highest number of treatments per animal and year (24). There were large differences between the number of cattle perceived by the keepers to be infected, and the number detected from blood sampled, among Abigar, Gurage and Horro. Sheko livestock keepers were better at correctly diagnosing trypanosomosis in their animals. It is concluded that Sheko cattle have higher trypanotolerance attributes of the breeds investigated and a better use of this breed could improve cattle health and household welfare in tsetse-infested areas.     

Livestock keeper perceptions of four indigenous cattle breeds in tsetse infested areas of Ethiopia

Four cattle breeds indigenous to western and south-western Ethiopia - Abigar, Gurage, Horro and Sheko - were included in a study of the perceptions of smallholder cattle keepers regarding cattle management, production levels and constraints for production. A semi-structured questionnaire was used and 60 cattle keepers from each of the four areas were interviewed. Diseases were reported as the main constraint to cattle production by a majority of livestock keepers in all areas except in the Sheko area, where over-stocking was the main constraint. Among diseases, trypanosomosis was the main livestock disease according to more than half of Gurage, Horro and Sheko keepers, whereas anthrax was most important in the Abigar area. Gurage had highest age at first calving, longest calving interval and also the lowest milk production, whereas Sheko and Abigar had the most favorable characteristics both for milk production (600–700 kg) and fertility (age at first mating 3–3.5 years and above 8 calves/cow). Cattle keepers in the Sheko area reported relatively less problems with cattle diseases compared to the other areas, especially regarding trypanosomosis. Abigar showed a different disease pattern than the other breeds and may also have advantages as regards trypanotolerance.     

Growth and Mortality in Sheep and Goats under High Tsetse Challenge in Kenya

Trypanosomosis is a major impediment to livestock production and economic development in those areas of Africa where it is endemic. Although small ruminants appear to perform better than cattle in various agro-ecological zones, the importance of trypanosomosis has not been extensively investigated in these livestock. This study was designed to investigate the prevalence of trypanosomosis in sheep and goats in an endemic area and to evaluate the performance of different breeds under high tsetse challenge and the potential role of chemoprophylaxis in the control of the disease. The results showed that tsetse flies feed readily on small ruminants, and that these animals are susceptible to trypanosomosis. The Small East African goats acquired fewer infections than the Black Head Persian and Dorper sheep used in the study. In both sheep and goats, chemoprophylaxis with isometamidium chloride (Samorin, Rhone Merieux, Annecy, France) was protective, resulting in fewer infections and higher body weight gain. Trypanosomosis caused anaemia in both sheep and goats, and animals whose PCV fell below 15% rarely recovered, even with trypanocidal drug treatment. The peak transmission period was between 1 and 3 months after the peak tsetse fly density, which raises the possibility of effective strategic prophylaxis.     

Estimating the Effects of Tsetse Control on Livestock Productivity – A Case Study in Southwest Ethiopia

A tsetse control campaign was started in January 1991 using a synthetic pyrethroid cypermethrin 'pour-on' applied monthly to cattle exposed to high levels of drug-resistant trypanosomes in the Ghibe valley of southwest Ethiopia. In December 1992, a cost-recovery scheme was introduced, and thereafter farmers paid for treatment. An average of 100 village Ethiopian Highland Zebu cattle were monitored monthly from March 1986 to February 1997. Individual animals in this herd were treated with diminazene aceturate (Berenil, Hoechst, Germany) at 3.5 mg/kg when trypanosomes were detected and their packed cell volume was less than 26%. Superimposed on this systematic trypanocidal chemotherapy, control of tsetse resulted in average reductions from 1992 to 1996 of 95% and 75% in the mean relative densities of tsetse and biting flies, respectively, and of 63% in the prevalence of trypanosomal infections in cattle. Despite these reductions, there was no significant increase in the body weight of the cows, calving rate or the mean body weight of calves at 12 months of age. There was, however, an average decrease of 57% in calf mortality (including still births) by 12 months of age, an increase of 49% in the ratio of live calves under 12 months of age to cows over 36 months of age, and an increase of 8% in the body weight of adult males.     

A survival analysis of trypanosomosis diagnostic-test performance under natural infection challenge

Little is known about the time-to-first detection and the time difference (TD) between first parasitological and first serological diagnosis of Trypanosoma spp. infections under natural infection challenge in cattle. The objective of our study was to estimate these measures of "longitudinal aspects" of diagnostic performance and to investigate potential biological factors. Emphasis was on diagnosis at the genus level (Trypanosoma spp.). Twelve N'Dama, 12 Gobra zebu and 12N'DamaxGobra (F1) crossbred cattle (all animals non-infected at the start of the experiment, six male and six female animals in each cohort) were exposed to natural high tsetse challenge in the Niamina East area in The Gambia [Acta Trop. 71 (1998) 57]. The animals were investigated parasitologically (detection of trypanosomes by buffy-coat technique), serologically (detection of T. brucei, T. congolense and T. vivax antigen by enzyme-linked immunosorbent assay (ELISA)) and clinically (packed-cell volume, PCV) over a period of 180 days. The time-to-first detection of trypanosomes, trypanosomal antigen (cut-off as suggested by test supplier) and drop in PCV (subject-based cut-off values) were recorded as outcomes of interest. Thus, incidence was both parasitologically (I(p)), serologically (I(s)) and clinically (I(c)). Recurrent events were not considered. The TD between first parasitological and first serological detection was established as I(s) time minus I(p) time. The effect of breed and sex on the time-to-first detection and on TD was investigated using Cox (proportional hazard) regression and ANOVA, respectively.We found that time-to-first parasitological detection of trypanosomosis in N'Dama animals was significantly longer than in the two other breeds (Cox regression, P=0.002). A similar but less-strong (P=0.063) effect of breed on time-to-first detection of trypanosomal antigen was found, whereas no breed effect was observed for clinical detection (P=0.432). Sex had no effect in all detection systems. The TD varied between -56 and 115 (mean 28). Marked differences among breeds and between sexes were not observed (ANOVA, P=0.8). We suggest that incidence studies are more suitable for detecting risk factors for animal trypanosomosis than prevalence-based (cross-sectional) studies because the latter often result in misinterpretation of factors that increase the survival time with infection as risk factors.     

The area-wide epidemiology of bovine trypanosomosis and its impact on mixed farming in subhumid West Africa; a case study in Togo.

This paper reports on an area wide study of all major variables determining the expression of trypanosomosis in cattle in the subhumid eco-zone of West Africa, taking Togo as an example. To enable systematic area-wide sampling, the country was divided in 311 grid-squares of 0.125 x 0.125 sides. Cross-sectional surveys were then conducted to generate maps or digital layers on cattle density, herd structure, ownership and breed. These data layers, except for the breed data, were subjected to a cluster analysis in order to define spatial patterns in animal husbandry systems. This analysis revealed two main systems: one is oriented towards integration with crop-agriculture and a second towards investment in cattle. These two systems could be further characterised by incorporating breed data. Zebu cattle and their crossbreeds are more favoured in the second system. The breed distribution map shows the actual situation but also serves to predict the outcome of progressive crossbreeding. An area wide trypanosomosis survey allowed the production of prevalence maps for Trypanosoma congolense, T. vivax and the associated packed cell volume (PCV) values. A simple curvi-linear relationship was established between vector density and disease prevalence. The regression between disease prevalence and PCV for taurine and zebu plus crossbreeds separately, revealed that taurine cattle maintain a comparatively high PCV level particularly in high prevalence scenarios. The relationship between the average herd PCV and cattle density suggests that herd PCV value may provide a mirror for the number of animals not kept because of the prevailing risk. The regression between agricultural intensity and cattle density subsequently in areas with decreasing herd PCV values reveals that the level of integration of cattle in crop production decreases with a decreasing PCV. Thus, despite the presence of taurine animals in Togo, the omnipresence of tsetse in particular Glossina tachinoides, remains a major obstacle to cattle raising and indirectly mixed farming development and intensification. It is argued that only with the present type of wide scale, spatial studies it becomes possible to clarify all the major variables influencing the expression of trypanosomosis. Spatial epidemiological studies at a macro level may form the basis for area wide trypanosomosis control in West Africa.     

Prevalence and incidence of bovine trypanosomosis on the Adamaoua plateau in Cameroon 10 years after the tsetse eradication campaign

Between March 2004 and February 2005, the monthly incidence of trypanosome infections was measured in cattle from nine sentinel herds in the Adamaoua province of Cameroon. Three herds of 20 cattle each were kept on the plateau which has been cleared from tsetse flies about 10 years ago, three other herds were grazing in the tsetse infested valley whereas the last three were herded in the buffer zone. The cross-sectional study showed that the initial trypanosomosis prevalence was 1.8, 5.2 and 2.0% on the plateau, in the buffer zone and the valley, respectively. During the longitudinal study, the trypanosomosis incidence was high in the valley (3.7-20%) and the buffer zone (1.8-13.4%), whereas it was significantly lower (0-2.1%) on the plateau. Tsetse flies, mainly Glossina morsitans submorsitans and a few G. tachinoides, were caught in the valley and the buffer zone, but none on the plateau. The data indicate a low trypanosomosis risk on the plateau. Further entomological studies, however, are required to clarify the origin of the trypanosome infections on the plateau.     

Study on the susceptibility of Sahel goats to experimental Trypanosoma vivax infection

Sahel goats, also known as Borno whites are found in the northern semi-arid, tsetse free Sahel region of Nigeria. They are transported alongside cattle from this zone to all other zones in the country, including the tsetse-infested zones, for commercial purposes and are kept for some time in these tsetse-infested zones until they are sold. This study therefore assessed the susceptibility of this breed of goats to trypanosome infection and its response to treatment with Berenil. Six bucks were inoculated intravenously with Trypanosoma vivax through the jugular vein while two served as uninfected control. The mean pre-patent period was 4.5 days and increasing parasitaemia followed the establishment of infection. Onset of parasitaemia was associated with increase in rectal temperature in all the infected goats and the temperature peak coincided with the only parasitaemic peak second week post-infection. The infected goats were treated with Berenil (Hoechst, Germany) 3.5mg/kg body weight at 4 weeks post-infection. The packed cell volume (PCV) continued to fall from a mean 30.73+/-0.01% pre-infection to a mean 13.21+/-0.18% at 1 week post-treatment. Deaths were recorded for 4 of the infected goats 1 week post-treatment while the remaining two died 2 weeks post-treatment, not responding to treatment.     

Parasitological prevalence of bovine trypanosomosis in Kindo Koisha district,Wollaita zone,south Ethiopia

A cross sectional survey to determine the distribution and prevalence of trypanosomosis was conducted in Kindo Koisha district, in the Wollaita zone in southern Ethiopia. A total of 1 008 adult cattle was examined at eight different localities. Dark field examination of the buffy coat, as well as stained thin blood film examination and packed cell volume (PCV) evaluation were the diagnostic techniques used. The overall prevalence of bovine trypanosomosis was 15 %. Among the positive animals, 108 (71.1%), 43 (28.4%) and 1 (0.6%) were due to Trypanosoma vivax, Trypanosoma congolense and mixed infection (T. vivax and T. congolense), respectively. The infection rate of T. vivax and T. congolense varied significantly (P < 0.01). The mean PCV of the positive and negative animals ranged between 18.3-32.1% and 26.8-33.4%, respectively. The mean PCV of negative animals (28 %) was significantly higher than the mean PCV of positive animals (22.3%) (P < 0.001). There was an inverse association of PCV with the prevalence of trypanosomosis (P > 0.05). The herd average PCV values of each site decreased with increasing proportion of the positive herds of that particular site. Of the diagnostic tests employed, the microhaematocrit buffy coat technique is relatively sensitive and it has an added advantage of indicating the general condition of the animal by haematocrit measurement. In view of the risk of trypanosomosis, a control intervention through the strategic application of appropriate trypanocidal drugs is recommended. A tsetse fly control scheme to reduce host-tsetse fly contact is equally as important as chemotherapy and chemoprophylaxis against trypanosomosis.     

Estimation of tsetse challenge and its relationship with trypanosomosis incidence in cattle kept under pastoral production systems in Kenya

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 enzyme-linked 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.     

Health and productivity of traditionally managed Djallonke sheep and West African dwarf goats under high and moderate trypanosomosis risk.

Trypanosome infections, packed red cell volume levels (PCV), body weight and nematode faecal egg counts of village-based small ruminants were monitored in two areas in The Gambia with either moderate or high trypanosomosis risk for 24 and 30 months respectively. Outflows from the flock and new-born animals were recorded and data on housing and management were compiled. Reported mortality rates were higher in goats than in sheep, but for both species highest in the moderate risk area. The peak of trypanosome infections lagged the peak of tsetse densities by 1-3 months in both areas. Trypanosoma vivax was the predominant species found in the infected animals, followed by T. congolense. Trypanosome prevalence was, in general, higher in sheep than in goats but only significantly higher during Year 1 in the moderate risk area. Trypanosome infection reduced the PCV level significantly and seasonal effects indicated significantly lower PCV levels during the rains. Trypanosome infection significantly depressed weight gain in both species at periods where infection rates were highest. In both species considerably lower weight gains were observed during the rainy season. Abortion rates were higher in goats than in sheep in both study sites, and highest in the high-risk site. Trypanosome infection in ewes in the high risk area increased lamb mortality significantly but had no effect on birth weights, nor on growth rates up to 4 months. Offspring mortality up to 4 months was generally high at both sites. Trypanosome infection in the dam between 3.5 to 7 months post parturition significantly increased parturition interval in both species. Peak faecal egg output occurred at the end of the rainy season and was highest for both species in the moderate risk site. Poor grazing management was found responsible for a seasonal nutritional constraint. Based on these results, these breeds of sheep and goats can be considered as trypanotolerant since they are able to remain productive under high and moderate levels of trypanosome challenge. Nevertheless, trypanosomosis affected their health and production level as shown by reduced PCV levels, depressed weight gains, longer parturition intervals and higher lamb mortality. In addition, during the rains, helminth infections and poor management leading to nutritional constraints had also a negative impact on health and production and therefore influenced the innate resilience to trypanosomosis in those indigenous breeds. Adaptations in management may have an equal impact as certain disease control measures to improve biological and economical returns from small ruminants in tsetse infested rural areas.     

Breed and trait preferences of Sheko cattle keepers in southwestern Ethiopia

Like their smallholder subsistence counterparts in developing countries, breed and trait preferences of Sheko cattle keepers have broad perspectives. Our study has documented breed and trait preferences of Sheko cattle keepers in southwestern Ethiopia—the natural breeding tract of Sheko cattle. Our results showed that due to their multifunctionality, cattle are the most preferred livestock species. Overall, farmers showed slightly more preference to local Zebus over Sheko breed. This is due to voracious feeding behavior of Sheko cattle, which make them less preferable in the face of worsening feed shortage, and due to aggressive temperament of Sheko cattle. This is despite Sheko's outperforming potential over local Zebus in their milk production, draft power, and hardiness. At trait level, overall milk production was consistently reported as the most preferred trait followed by fertility and traction. This trait preference rank has matched with the reported frequency count ranks for Sheko cattle use. However, breed preference rank has not matched with reported trait preference ranks because Sheko excels local Zebus in all the three most preferred traits, but it was ranked second. Therefore, to minimize these conflicting interests, breed management plans for Sheko cattle should target on strategies that help to solve feed shortage problem and to improve feeding practices, and on selection of less aggressive Sheko cattle. Therefore, these strategies should be considered in line with Sheko cattle conservation and genetic improvement programs.     

Serum haemolytic complement activity and C3 levels in bovine trypanosomosis under natural conditions of challenge--early indications of individual susceptibility to disease

Twenty-five Baoule (Bos taurus) and 12 Zebu (Bos indicus) cattle, which were part of an experiment aimed at characterizing cattle for resistance to trypanosomosis under natural challenge in Burkina Faso, were monitored for complement levels. Total haemolytic activity of the alternative complement pathway and C3 in sera taken weekly were estimated. The results were analysed in relation to the course of the disease, parasitological data, packed red cell volume (PCV) and body weight. All the animals became infected with Trypanosoma vivax and/or T. congolense. The Zebu had to be treated with Berenil (Diminazene aceturate, Hoechst, W. Germany) after a mean period of 5 weeks of infection, whereas 7 of the 25 Baoule remained in good condition throughout the experiment. The remaining 18 Baoule required treatment after a variable period of infection. There was a decrease in haemolytic complement activity (HC') as well as in C3 levels, which coincided with the first detection of parasites in the blood. The titres in the Zebu fell to 10-20% of pre-infection level within 2-3 weeks and they showed no tendency towards regaining normal levels. The drop in complement in the Baoule was less pronounced and was in most cases followed by an increase approaching normal values. In these animals, the complement level in early infection was found to depend on the intensity of parasite load and on the control potential of each individual. There was a significant correlation between minimum complement activity (min. HC'), minimum C3 (min C3) and minimum PCV (min.PCV) in early infection. These three parameters correlated with individual resistance and might, therefore, be useful criteria for the identification of the most resistant individuals within a trypanotolerant breed.     

Studies on the epidemiology of trypanosomiasis in sheep and goats in Kenya

The epidemiology of trypanosomiasis in a tsetse-infested range area of Kenya was studied for 2 years in various breeds of sheep and goats. Observations, including infection rates, PCV, temperature and weight loss indicated that the exotic breeds were more susceptible to natural trypanosomal infection than the indigenous breeds and that the infection may be severely debilitating and in many cases fatal. Observations of tsetse numbers and rainfall in the grazing area during the first year showed that there was a significant correlation between tsetse numbers and rainfall of the previous month. The increase in tsetse numbers, which occurred one month after substantial rainfall, was followed by an increase in the prevalence of trypanosomiasis in the animals. However, during the second year when rainfall was low there was no correlation between tsetse numbers and rainfall. It was concluded that the seasonal incidence of trypanosomiasis and the possible trypanotolerance of the indigenous breeds are important factors to be considered when initiating a small stock improvement programme for trypanosomiasis-endemic areas.     

Bovine trypanosomosis in the Upper West Region of Ghana: entomological, parasitological and serological cross-sectional surveys

Baseline surveys were conducted in the Upper West Region of Ghana to assess the distribution and densities of tsetse species, as well as the prevalence of bovine trypanosomosis. The entomological survey was designed to cover the suitable tsetse habitats along the three main rivers in the study area (i.e. Black Volta, Kulpawn and Sissili). Results indicated the presence of Glossina tachinoides in all three river basins, whilst Glossina palpalis gambiensis was only found close to the southern limit of the study area. A random sampling of 1800 cattle of the West African Short Horn, Sanga and Zebu breeds from 36 randomly selected grid cells covering the study area showed substantial differences between parasitological and serological prevalences. The average parasitological prevalence was estimated at 2.5% (95% CI: 1.06-5.77) with the majority of the infections due to Trypanosoma vivax. Most of the infected cattle were found close to the major river systems. The serological prevalence, measured using Enzyme Linked Immunosorbent Assay (ELISA), test was 19% (95% CI: 14.03-25.35). Cattle with anti-trypanosomal antibodies were also found throughout the study area.     

Studies on Haemoglobin Polymorphism of Two Breeds of Iranian Sheep and Its Relationship to Concentrations of Iron,Copper, Haemoglobin,Haematocrit and RBC number

After electrophoresis on cellulose acetate, two haemoglobin phenotypes were detected in Baloochi and Kordi breeds: AA and AB phenotypes. AA was commonest in two breeds. The incidence of type AB haemoglobin in Baloochi and Kordi breeds was 26.5% (9/34) and 9.5% (2/21), respectively. BB phenotype was not seen in Baloochi and Kordi breeds. In sheep with AB phenotype, haemoglobin B was dominant. The mean +/- SD of the two kinds of haemoglobin in sheep with AB phenotype were haemoglobin B percentage 60.5% +/- 9.04%, haemoglobin B absolute 73.84 +/- 5.44 g/L, haemoglobin A percentage 39.5% +/- 9.04%, haemoglobin A absolute 32.88 +/- 2.89 g/L. There were no significant differences for total haemoglobin, haematocrit, red blood cell (RBC) number, iron and copper levels between breed, sex and age groups and also between sheep with AA phenotype and AB phenotype. Pearson's method showed significant correlations for total haemoglobin with packed cell volume (PCV), RBC number, copper concentration and RBC number with PCV, copper level and PCV with copper amount and copper concentration with iron level (p<0.05). In the Kordi breed, significant correlations were seen for total haemoglobin with PCV, RBC number, copper concentration and PCV with RBC number and RBC number with copper level and copper concentration with iron amount (p<0.05). In the Baloochi breed, significant correlations were detected for total haemoglobin with PCV, RBC number and PCV with RBC number (p<0.05).     

Implications of the re-invasion of Southeast Uganda by Glossina pallidipes on the epidemiology of bovine trypanosomosis

A study to assess the influence of re-invasion of Glossina pallidipes on the epidemiology of bovine trypanosomosis was conducted in Southeast Uganda. A total of 1,992 cattle were screened in villages, with (949) and without G. pallidipes (1043) for trypanosomosis using a combination of the BCT and HCT methods. The prevalence of trypanosomosis (15.5%), Trypanosoma brucei infection (1.4%), T. congolense infection (7.2%), T. vivax infection (5.3%) and mixed infection (1.6%) in cattle in villages with was significantly higher than in those without G. pallidipes: trypanosomosis (7.1%), T. brucei infection (0.6%), T. congolense infection (2.0%), T. vivax infection (3.3%) and mixed infection (1.2%) (overall trypanosome infection, chi2=35.5, d.f.=1, P<0.05; T. brucei infection, chi2=8.06, d.f.=1, P<0.05; T. congolense infection, chi2=22.8, d.f.=1, P<0.05 and T. vivax infection, chi2=6.4, d.f.=1, P<0.05). Infections of Trypanosoma congolense were predominant in cattle in villages with G. pallidipes, while T. vivax infections were predominant in cattle in villages without. In all villages, T. brucei infections were fewer than either T. congolense or T. vivax infections. The risk of transmission of T. brucei, T. congolense and T. vivax infections was 3, 2.7 and 1.6 times, respectively, higher in villages with G. pallidipes than in those without, despite the presence of G. f. fuscipes in either set of villages. The mean PCV (28.27+/-0.41, 95% CI) and mean herd size (3+/-0.46) of cattle in villages with G. pallidipes were significantly (P<0.05) lower than in those in villages without (mean PCV, 29.48+/-0.34; mean herd size, 4+/-0.72). It is evident that presence of G. pallidipes brings about an increase in the prevalence of T. congolense, which causes a more severe disease in cattle than other species of trypanosomes. This is a rare case of a re-invasion of a tsetse species whose disease transmission capability calls for refocusing of the traditional national tsetse and trypanosomosis control strategies to contain it.     

Bovine trypanosomosis and its vectors in two districts of Bench Maji zone,South Western Ethiopia

A cross-sectional study was carried out from November 2008 to February 2009 in Guraferda and Sheko districts of Bench Maji Zone, South Western Ethiopia. The objective of the study was to determine the prevalence of bovine trypanosomosis and the density of its vectors. An overall prevalence of trypanosome infection in the study area was 4.4%. Trypanosoma congolense (36.36%) was the dominant trypanosome species followed by Trypanosoma vivax (18.18%) and Trypanosoma brucei (9.09%). Mean packed cell volume value of parasitemic animals (21.8%) was significantly (P < 0.05) lower than that of aparasitemic animals (27.7%). Biconical and NGU traps were deployed for 72 h, and the result indicated Glossina pallidipes followed by Glossina fuscipes as the only tsetse fly species caught in the study area along with other biting flies like Stomoxys and Tabanus. The apparent density of tsetse flies was 2.83 flies trap⁻¹ day⁻¹. NGU trap caught more of G. pallidipes while biconical trap caught more G. fuscipes, and the difference was significant (P < 0.05). Although the current study indicated low prevalence of trypanosomosis in the study area, the impacts of trypanosomosis on cattle production and productivity should not be neglected. Therefore, attention should be given to control the disease and also the vector.     

Relative resistance of Dorper crossbred ewes to gastrointestinal nematode infection compared with St. Croix and Katahdin ewes in the southeastern United States

A study was conducted to evaluate relative resistance of Dorper crossbred (DO), Katahdin (KA), St. Croix (SC), and Hampshire (HA) ewes to natural and experimental gastro-intestinal (GI) nematode infection over a 20-month period. The objective of Experiment 1 was to evaluate breeds for resistance to infection acquired naturally from mixed grass pastures. In Year 1 (May-December 2000) de-worming of ewes occurred during wet, hot conditions in July and during late pregnancy in December. In Year 2 (January-December 2001), ewes were de-wormed after fecal egg count (FEC) for a breed group rose above 1000 eggs per gram (epg) or after blood packed cell volume (PCV) of an individual ewe fell below 20. FEC was determined every 28 days and PCV every 14-28 days. In both the years, ewes were pastured together, except during the 28-days breeding periods, on tall fescue, bermudagrass, or ryegrass, and rotated among pastures dependent on forage availability. Ewes were in good or excellent condition (body condition score of 3-4 out of 5) throughout the study. The objective of Experiment 2 was to evaluate the breeds for relative resistance to an experimental infection with Haemonchus contortus infective larvae. Both PCV and FEC were determined every 7 days from 14 to 42 days after inoculation with 30000 infective larvae per ewe. In Experiment 1, Year 1, FEC was slightly greater and PCV was lower from July to September in DO ewes (breed x time, P<0.001). In Year 2, de-worming occurred 14 days later in DO ewes compared with other breed types. Otherwise PCV and FEC were similar among the hair breeds and higher and lower, respectively, compared with HA ewes (breed x time, P<0.001). In Experiment 2, FEC and PCV were similar among hair breeds; FEC was lower and PCV higher in hair breeds compared with that of HA ewes (P<0.01). Relative resistance of mature Dorper crossbred ewes was comparable to that of Katahdin and St. Croix ewes and superior to that of Hampshire ewes.     

Ghibe river basin in Ethiopia: Present situation of trypanocidal drug resistance in Trypanosoma congolense using tests in mice and PCR-RFLP

A cross-sectional study was carried out in the Ghibe valley from August to October 2010. 411 head of cattle were sampled in eight villages for buffy coat examination (BCE) and blood spots were collected from each animal for trypanosomose diagnosis by 18S-PCR-RFLP and diminazene aceturate (DA) resistance by Ade2-PCR-RFLP. Three villages were selected in a zone where trypanosomosis control operations are currently on-going whereas the other 5 villages were located outside these control operations. Twenty-four samples (5.84%) were diagnosed positive for Trypanosoma congolense by BCE and injected in mice for further characterization. Twelve of those isolates successfully multiplied in mice and were tested by an in vivo mouse test for diminazene (DA) (10 and 20mg/kg B.W.) and isometamidium (ISM) (1mg/kg B.W.) resistance. All were shown to be resistant to both drugs at all doses. The use of the Ade2-PCR-RFLP on these isolates confirmed their DA-resistance profile. Seventy-three of the collected blood spots (17.8%) were diagnosed positive for T. congolense by 18S-PCR-RFLP of which 37 (50.7%) gave amplification products with the Ade2-PCR-RFLP. Here, 35 (94.6%) showed a resistant profile, 1 (2.7%) a sensitive profile and 1 (2.7%) a mixed profile. The data were analysed by logistic regression model and the relapsing time in mice tests was assessed using the Cox regression model. There was no significant intervention effect (P=0.83) with odds ratio equal to 1.21 when using the BCE data. 18S-PCR-RFLP test also showed no significant intervention effect (P=0.60) with odds ratio equal to 1.43. The hazard ratio of getting parasitaemic after treatment with DA at 20mg/kg B.W. compared to the control group was 0.38 which differs significantly from one (P<0.001). Relapsing time after treatment with DA 10mg/kg B.W. or ISM 1mg/kg B.W. was also significantly longer than the prepatent period of the control group. The situation of drug resistance in the Ghibe valley is further discussed.