Prevalence of Bovine Trypanosomosis and Apparent Density of Tsetse and Other Biting Flies in Mandura District, Northwest Ethiopia

A cross-sectional study was conducted from May to June 2014 to determine the prevalence of bovine trypanosomosis and the apparent density of tsetse and other biting flies in four peasant associations of Mandura district. For the prevalence study, dark phase contrast buffy coat examination and Giemsa stained thin blood smears were used. Whereas for the entomological survey and apparent density of flies, traps were deployed. The entomological survey indicated that Glossina tachnoides was the only tsetse fly species caught in the study area along with other biting flies like Haematopota, Stomoxys and Tabanus. Apparent tsetse flies density of 0.06 flies/trap/ day was recorded in the district. For the prevalence study, out of a total of 405 cattle examined, 22 (5.43%) were found infected with trypanosomes. Highest prevalence was recorded in cattle with poor body condition (7.06%) followed by medium (5.20%) and god (3.92%). This study showed no significant difference (P>0.05) in trypanosomosis infection rate among peasant associations, age, body condition and sex of the animal. The overall mean PCV value of examined cattle is 29.29 ± 4.813 (׀t׀=122.49; df=404; P=0.00). The mean PCV of non infected cattle was slightly higher (29.30%) than that of infected animals (29.27%). Among the species of trypanosomes isolated, Trypanosoma vivax was identified to be the major causes of trypanosomosis in the study area accounting for 81.82% of the total infections observed followed by Trypanosoma congolense (18.18%). Taken as a whole, the present work evidenced that tsetse and trypanosomosis has continued to pose a considerable threat to cattle of the study area warranting an integrated control to safeguard cattle production and productivity. Prevalence of Bovine Trypanosomosis and Apparent Density of Tsetse and Other Biting Flies in Mandura District, Northwest Ethiopia


Introduction
Trypanosomosis is a complex disease caused by unicellular parasites found in the blood and other tissues of vertebrates including livestock, wild life and people. The most important trypanosome species affecting livestock in Ethiopia are Trypanosoma congolense, Trypanosoma vivax, and Trypanosoma brucei in cattle, sheep and goats, Trypanosoma evansi in camels and Trypanosoma equiperdium in horses [1].
The influence of tsetse on African agriculture through the transmission of trypanosomosis continues to be a major constraint to the development of national economies and their achievement of self sufficiency in basic food production. The general distribution of tsetse flies is determined principally by climate and influenced by altitude, vegetation, and presence of suitable host animals [2]. Tsetse flies in Ethiopia are confined to southern and western regions between longitude 33 0 and 38 0 East and latitude 5 0 and 12 0 North which amounts to about 200,000 Km 2. Tsetse infested areas lied in the low lands and also in the river valleys of Blue Nile, Baro Akobo, Didessa, Ghibe and Omo. Out of the nine regions of Ethiopia five (Amhara, Beninshangul Gumuz, Gambella, Oromia and Southern Nation Nationalities and peoples) are infested with more than one species of tsetse flies [3]. To date five species of Glossina (Glossina morsitans submorsitans, G. Pallidipes, G. tachnoides, G. f. fuscipes and G. longipennis) have been recorded from Ethiopia [3]. Apart from the cyclical transmission of trypanosomosis by the Glossina species, it is highly considered that mechanical transmission is a potential threat to livestock productivity in some parts of Ethiopia [1].
In Mandura district trypanosomosis was found to be one of the factors that hampered livestock rearing in most peasant associations. Therefore, a study on the status of the disease and investigating the vectors and their relative abundance is crucial for a successful control in the area. Therefore, the present work aimed at determining the prevalence of bovine trypanosomosis and apparent density of tsetse and other biting flies ascribed in the transmission of trypanosomosis.

Study area and period
The study was conducted from May to June 2014 in Mandura district located in Metekel zone of Benishangul Gumuz regional sate, situated at 547 Kilometers North West of Addis Ababa. The mean annual rain fall in Mandura district ranges from 900-1400 mm. The annual temperature ranges from 28-30oC. The district has altitudes ranging from 1000-1400 m. a. s.1. The district is located in Blue Nile valley. The areas have got a number of wild animals, such as African buffaloes, Bush pigs, warthog, bush buck, kudu, hippopotamus, crocodiles, hyena, antelopes and snakeswhich are claimed to serve as sources of food for the fly as reservoir for trypanosomes.

Study population
The cattle in the district are local breeds that are kept under

Sample size determination
Sample size was determined using 95% confidence level, 50% expected prevalence and 0.05 desired absolute precision using the formula described by Thrustfield (2005). Therefore, a total of 384 cattle were needed for the study. However, sample was collected from 405 animals to increase precision.

Study Design and protocol
A cross-sectional study design was employed. For the trypanosomosis prevalence study, dark phase contrast buffy coat examination and Giemsa stained thin blood smears were used. Blood sample collection was performed by piercing the marginal ear vein with a sterile lancet and blood was drawn by a heparinized capillary tube. Then one end (the heparanized end) of capillary rubes were sealed with crystal sealant and centrifuged at 12,000 rpm for five minutes to separate the blood cells and to concentrate trypanosomes using centrifugal forces, as buffy coat. Then the PCV was determined and recorded. The capillary tubes were then broken just below buffy coat using diamond pencil and expressed on microscopic slide and covered with a cover slip. Then it was examined under 40× objective of microscope to detect the presence of the parasites [4]. Trypanosome species were identified using Giemsa stained thin blood films. For the entomological survey, a total of 57 baited traps were deployed along suitable tsetse habitats to assess the apparent densities, distributions and species of tsetse flies and other biting files involving in transmission of trypanosomosis. All traps were baited with acetone, Octenol (1-3-Octane) and cow urine filled in separated bottles and labeled and deployed at an interval of 200-250 meters. The coordination and altitude of each trap were recorded using GPS. The vegetation type, the prominent feature within 100 m radius and the canopy of each trap were recorded. After 48 hours of trap deployment, the cages were collected and captured flies were identified and sexed according to morphological characteristics and counted. The tsetse flies were identified to species level and the other biting flies to the genus level.

Data management and analysis
Raw data were entered into a Microsoft Excel spreadsheet and descriptive statistics were used to summarize the data. The prevalence was calculated for all data as the number of infected individuals divided by the number of individuals examined and multiplied by 100. The association between the prevalence of trypanosome infection and risk factors were assessed by logistic regression, whereas the student's t-test was used to assess the difference in mean PCV between trypanosome positive and negative animals. All statistical analyses were conducted using SPSS version 20.0 software. The test result was considered significant when the calculated p-value was less than 0.05. The density of fly population was calculated by dividing the number of files caught by the number of traps deployed and the number of days of deployment and expressed as fly /trap/ day (FTD).

Entomological survey result
A total of 57 mono-pyramidal, bi-conical, mono-conical and NGU traps were deployed in the district ( Table 1). As indicated in Table 1, the apparent density of tsetse flies is 0.06 fly/trap/day. Few riverine species particularly Glossina tachnoides was caught from the district. Out of total caught tsetse flies, 28.57% were male and 71.43% were female. Other biting flies including Stomoxys (52), Tabanus (12) and Haematopota (519) species were also caught. The apparent density of Tabanus, Haematopota and Stomoxys were 0.11, 4.55 and 0. 46 f/t/d respectively. Large number of Musca Species were also caught but discarded because they have no role in the transmission of trypanosomosis.

Haematological survey result
The overall mean PCV value of examined cattle was 29.29 ± 4.813 ‫;94.221=|‪t‬|(‬ df=404; P=0.00, 95%CI=28.82-29.79). The mean PCV of non infected cattle was slightly higher (29.30%) than that of infected animals (29.27%). In fact the difference in mean PCV between parasitaemic animals and aparasitaemic animals indicated that trypanosomosis may be involved in adversely lowering the PCV values of infected animals.

Discussion
In the present study, the apparent density of tsetse flies caught   The survey revealed that the overall trypanosome prevalence was 5.43%. This result is consistent with the work of Teka et al. [5] which reported 4.43% bovine trypanosomosis prevalence in selected villages of Arba Minch; Adale and Yassine [7] which reported 6.3% in Wolaita zone of Kindo Koish district, Southern Ehiopia; Degneh et al. [8] reported 6.86% in Lalo Kile district of Oromia regional state; Alamayew et al. [9] which reported 6.9% in Chena district, south west Ethiopia and Denbarga et al. [10] which reported 4.2% in South Achefer district, Northern Ethiopia.
Highest infection rate (6.82%) was recorded Ejenta village and the lowest was in Esitsa (3.45%). The Prevalence among districts and Peasant associations in this study could be attributed to the tsetse fly and/or other biting flies' population and type present in each peasant association which is dependent on micro climate, animal heard density, distance between herds and other various factors [18].
The proportion of Trypanosoma vivax in all sites of this study was higher (81.82%) followed by T. congolense (18.18%). This result is consistent with the report by Cherenet [19] and Cherenet et al. [20] in tsetse free areas of Amhara region. This result disagreed with the report by Abebe and Jobere [21] in which they reported 58% of the total trypanosomes detected were T. congolense. Zecharias and Zeryehun [13] in Arbaminch and Mulaw et al. [22] also reported higher proportion of T. congolense than T. vivax. Such difference could possibly be attributed to the presence of major mechanical vectors and more efficient transmitters of T. vivax.
In this study, age-wise analysis revealed that there was no significant difference in prevalence between age groups though a highest infection rate was recorded in young ones (7.59%). These results disagree with that of Tasew and Duguma [23] and Dagnachew et al. [16].
The difference of prevalence of trypanosomosis among the body condition score was also not significant (p>0.05) being higher in poor body conditioned animals than other groups. This finding is similar to the report by Bacha et al. [24]. The prevalence of infection between sex categories was 4.68% for male and 5.98% for females, but there was no statistically significant difference between sex groups (p>0.05). Similarly, Daya and Abebe [25] and Teka et al. [5] also reported the same trend in susceptibility between the two sexes. This shows that both male and female cattle were more or less equally susceptible to trypanosomosis infection.
The overall mean PCV value of examined cattle was 29.29 ± 4.813 ‫;94.221=|‪t‬|(‬ df=404; P=0.00, 95%CI=28.82-29.79). The mean PCV of non infected cattle was slightly higher (29.30%) than that of infected animals (29.27%). In fact the difference in mean PCV between parasitaemic animals and aparasitaemic animals indicated that trypanosomosis may be involved in adversely lowering the PCV values of infected animals. Parasitaemic animals had generally lower mean PCV than the corresponding aparasitaemic ones, though there is appearing of parasitological negative animals within the PCV values of less than the threshold value. This may be due to in adequacy of detection method [4] or delayed recovery of anemic situation after current treatment with trypanocidal drugs and may be other blood parasites infection, malnutrition associated with long draught in the areas. While the occurrences of positive animals with PCV greater than 25% might be thought of recent infection of animals.

Conclusion
The present work showed a relatively low prevalence of trypanosomosis and apparent density of tsetse flies in Mandura district. However, this is an evidence not to be neglected that tsetse and trypanosomosis has yet continued to pose a considerable threat to cattle of the study area warranting an integrated parasite and vector control to safeguard cattle production and productivity.