Bovine trypanosomosis and its fly vectors in three selected settlement areas of Hawa-Gelan district , western Ethiopia

Copyright: © 2014. The Authors. Licensee: AOSIS OpenJournals. This work is licensed under the Creative Commons Attribution License. A cross-sectional study aimed at investigating the species diversity of fly vectors and estimating the prevalence of bovine trypanosomosis was carried out from October 2009 to May 2010 in selected settlement areas of the Hawa-Gelan district in the western Wollega zone of Ethiopia. Standard methods of sampling and identification were employed for both entomological and parasitological examination. Three species of the genus Glossina (Glossina pallidipes, Glossina morsitans submorsitans and Glossina fuscipes) and two genera of biting flies (Stomoxys and Tabanus) were caught and identified. The overall apparent density of Glossina species caught was 10.5 flies per trap per day, with a higher proportion of female flies (57.2%). Out of a total 389 cattle examined, 42 (10.8%; 95% CI: 7.89% – 14.3%) were found infected with trypanosomes. Three trypanosome species were detected in the study area, namely Trypanosoma congolense (54.8%), Trypanosoma brucei (23.8%) and Trypanosoma vivax (21.4%). The prevalence of trypanosomosis was found to be significantly (p < 0.05) higher in cattle with poor body condition. There was an association between mean packed cell volume (PCV) and the occurrence of parasitaemia (χ2 = 49.5, p < 0.05). About 95.2% of cattle that were positive for trypanosomes had a PCV less than the lower limit for cattle. Considering the current result, bovine trypanosomosis seems to be a serious constraint for agricultural activities in the settlement areas of the Hawa-Gelan district and seems to be associated with the presence of Glossina species. Therefore, application of control methods through community involvement to reduce the Glossina species infestation level is likely to increase animal productivity.


Introduction
Agriculture is the mainstay of the Ethiopian economy.A large part of the agricultural system is not mechanised, so livestock play a crucial role in agricultural production both directly as food sources and as a source of traction power.Trypanosomosis is a major constraint in the health and productivity of livestock and hence agricultural production in Ethiopia in general (Ministry of Agriculture [MOA] 1995).Annual losses to the national economy are estimated to exceed $200 million because of mortality and morbidity of livestock, denied access to land resources and the costs of controlling this disease (Taye et al. 2012;Vreysen et al. 1999).Approximately 220 000 km2 of otherwise agriculturally productive land in the western and south-western part of the country (MOA 1995) is estimated to be infested by five different species of tsetse flies (Glossina morsitans submorsitans, Glossina pallidipes, Glossina tachinoides, Glossina fuscipes fuscipes and Glossina longipennis) (Abebe 2005).
Of the species of trypanosomes recorded in Ethiopia, the most important trypanosomes in terms of economic loss in domestic livestock are the tsetse-transmitted species Trypanosoma congolense, Trypanosoma vivax and Trypanosoma brucei (Abebe 2005).About 14.8 million cattle, 6.1 million sheep and goats, 1 million camels and 1.2 million equines live in endemic areas (MOA 1995).
Currently, trypanosomosis is found to be one of the factors hampering livestock production and productivity in most settlement areas of western Ethiopia.An understanding of the prevalence of the disease and magnitude of the vector population is crucial for designing appropriate control strategies.The current study was planned and carried out to fill such gaps.Therefore, the aim of this research was to estimate the prevalence of trypanosomosis in cattle and relative abundance and species of both Glossina and other biting flies responsible for transmitting the disease in selected settlement areas of the Hawa-Gelan district.

Study area
The study was conducted from October 2009 to May 2010 in the Hawa-Gelan district, located in the Birbir valley, in the western Wollega zone of the Oromia region, Ethiopia.The altitude of the areas

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Bovine trypanosomosis and its fly vectors in three selected settlement areas of Hawa-Gelan district, western Ethiopia  1).The criteria for selection of the three settlement areas were based on their accessibility and nature of the habitat as well as farmers' complaints of the problem.

Study animals and sampling
The study animals were indigenous breeds of cattle kept under an extensive husbandry system that allows free grazing, usually mixed with other livestock species in selected settlement areas.A cross-sectional study design was followed to estimate the prevalence of trypanosomosis in cattle in the area.Hence, a total of 389 cattle were selected from the study animals by a systematic random sampling technique (see Thrusfield 2005) with a 95% confidence interval, 5% desired absolute precision, and 50% expected prevalence.(As the actual prevalence was unknown, 50% was used as the corresponding sample size is the largest.) The body condition status of selected animals was assessed and ranked as good, medium and poor (see Nicholson & Butterworth 1986).

Entomological data
The density and diversity of Glossina species were assessed using odour-baited biconical traps deployed at 200 m -250 m intervals.The odour baits used contained acetone, Octanol and aged cow urine.A total of 71 traps were used; 21, 26 and 24 were deployed in the riverside and wooded grassland areas of Settlement 21, Tulema and Settlement 17 respectively.Flies were collected from each trap after 48 h of deployment and then identified based on their morphology, as described by Uilenberg (1998) and Pollock (1982).

Parasitological and haematological data
Blood samples were collected from marginal ear veins using a heparinised micro-haematocrit capillary tube which was sealed on one side with Cristaseal (Hawksley Ltd, Lancing, UK).The capillary tube was then transferred to a haematocrit centrifuge and spun for 5 min at 1200 revolutions per minute.The centrifuged capillary tube was measured on a haematocrit reader to estimate the packed cell volume (PCV) as an indicator of anaemia.It was then cut 1 mm below the buffy coat (BC) and the contents of the tube expressed onto a slide, mixed and covered with a 22 mm x 22 mm cover slip.The slide was then examined with a 40x objective lens using phase contrast (Murray et al. 1983;Uilenberg 1998) or dark field microscopy to detect the presence of motile trypanosomes.For the purpose of species identification, a thin blood smear was prepared from the BC for those samples that were positive on BC examination and stained with Giemsa stain and examined under a microscope using the oil immersion 100x objective lens (Murray et al. 1983).

Data analysis
All statistical analyses were performed using STATA version 11.0 software (Stata Corp., College Station, USA).The proportion of vector flies (Glossina species and biting flies) caught per trap per day was computed to determine their relative abundance and species diversity.The prevalence of trypanosomosis was computed by dividing the number of infected animals by the total number of samples and multiplying the result by 100.The prevalence of trypanosome infection between the study variables (such as body condition and settlement areas) was compared by chi-square (χ 2 ) test of independence for significance.

Entomological results
Two genera of biting flies, Stomoxys and Tabanus, and three species of Glossina were encountered during the entomological survey.Glossina morsitans submorsitans, G. pallidipes and G. fuscipes were the species of Glossina caught during the period (Figure 2).The relative abundance of Glossina species and other biting flies is shown in

Mean caught
Tulema Settlement 17 per trap per day was computed from these values and is shown in brackets.The male and female proportions of each species are shown in Table 2.The male to female ratios of Glossina species were 1:1.4,1:1.3 and 1:1.2 for G. morsitans submorsitans, G. pallidipes and G. fuscipes, respectively.

Parasitological results
Out of 389 cattle examined, 42 (10.8%;95% CI: 7.9% -14.31%) were found to be infected with trypanosome species.The proportion of cattle infected in the three settlement areas is shown in Table 3.No significant variation was seen in the infection status between settlement sites (p > 0.05).
Of the 389 cattle examined, 95 (24.4%), 122 (31.4%) and 172 (44.2%) were in poor, medium and good body condition, respectively.More than half of the infected cattle (22 out of 42 or 52.4%) were those which were ranked as having poor body condition (Table 4).Therefore a significant association (p < 0.05) is observed between infection and body condition of animals.

Haematological findings
In this study, a PCV measurement of 25% and above was considered to be normal (Douglas & Wardrop 2010).The overall mean PCV of the cattle sampled was 26.6% (95% CI: 10% -41%).The mean PCV of parasitaemic cattle was 17.1% (95% CI: 10% -28%).There was a significant association between mean PCV and the occurrence of parasitaemia (χ 2 = 49.5, p < 0.05).About 95.2% of cattle that were positive for trypanosomes had a PCV less than the minimum value for cattle, whereas only 23.3% of aparasitaemic cattle had less than 25%.

Discussion and conclusions
In this study, the entomological findings revealed that three species of Glossina out of five reported in Ethiopia (Abebe 2005) Tilahun et al. 1999).This wider range is accounted for by differences in season and density of vegetation cover.The riverine vegetation and savannah habitats prevailing in the areas are very important for the widespread occurrence of Glossina species (Desta et al. 2013).
According to Leak (1999), vegetation is vital for providing suitable conditions.Glossina pallidipes is widespread in the bush vegetation type (Bancha 2001).
There was no significant variation between Settlement 21 and Tulema, which could be attributed to similarities in ecological situations characterised by bushes and grassland.However, there was a significant difference between Settlement 17 and the other two sites, which could be attributed to the difference in habitat for Glossina species.Settlement 17 is characterised by dense forest cover in addition to the grassland and bush coverage.Bancha (2001) also reported the highest total catch from the bush vegetation type.A higher proportion of female Glossina species (57.2%) was caught than male (42.8%), which is in line with various reports from the country (Bancha 2001;Daya & Abebe 2008;Desta et al. 2013).This could be attributed to the longer lifespan of female compared to male Glossina (Leak 1999).
Furthermore, a 10.8% overall prevalence of cattle trypanosomosis was detected in this study.This finding is generally in agreement with reports of studies carried out in the western part of Oromia State and the northern part of the Southern Nations, Nationalities and Peoples' Region (SNNPR), Ethiopia (Asha et al. 2008;Bogale, Wodajo & Chanie 2012;Daya & Abebe 2008;Rundassa et al. 2013;Tasew & Duguma 2012).The occurrence of trypanosome infections in cattle is clearly linked to the presence of potential fly vectors (Glossina species and other biting flies) in the study areas.The study was carried out in the late rainy and dry seasons of the year and therefore there was no significant difference in the prevalence of cattle trypanosomosis amongst the three settlement areas.This reflects the presence of continued Glossina challenge to cattle as the animals are driven to pasture and water sources, where they congregate.
In this study three species of trypanosomes were identified, namely T. congolense, T. vivax and T. brucei, in the ratio 2.6:1:1.1.These species are widespread in most parts of western Ethiopia (Abebe 2005; Mulaw, Addis & Fromisa 2011), and T. congolense was found to be the most prevalent when compared to other species.This finding is in agreement with various reports from the western part of the country (Abebe & Jobre 1996;Bekele et al. 2010;Mulaw et al. 2011;Rundassa et al. 2013).
This study also demonstrated an association between the body condition of cattle and the occurrence of trypanosome infections.This could be explained by the occurrence of infections in 52.4%, 28.6% and 19.0% of cattle with poor, medium and good body condition, respectively.The majority of the infected animals manifest clinically poor body condition, as trypanosomosis is characterised by progressive weight loss (Radostits et al. 2007).Poor body condition is not only a result of trypanosomosis, and could therefore also result from other pathogens and nutritional stress.
As established earlier (Marcotty et al. 2008;Van den Bossche & Rowlands 2001), this study also confirmed that the mean PCV of cattle with trypanosomosis is significantly lower than that of aparasitaemic animals.This finding is in agreement with various reports on local zebu from Ethiopia (Lemecha et al. 2006;Miruk et al. 2008;Stein et al. 2011;Tasew & Duguma 2012).According to Van den Bossche and Rowlands (2001), reduction of PCV is an indicator of trypanosomosis.
The results of the current study indicate that three species of Glossina and other biting flies that serve as potential vectors for trypanosomes infest the settlement areas of the Hawa-Gelan district and hence can sustain the occurrences of trypanosomosis in cattle.Glossina pallidipes, G. morsitans submorsitans and G. fuscipes were the common species of Glossina identified, whilst Trypanosoma congolense is frequently detected, followed by T. brucei and T. vivax.The relative abundance of Glossina species caught and the prevalence of cattle trypanosomosis investigated could indicate a serious problem in the area.Therefore, progressive control methods aimed at reducing the Glossina species burden would be necessary to minimise the impact of trypanosomosis.Success of control options depends on active community participation.Therefore, mobilising the community and increasing their participation in control activity could play a key role in reducing the impact of the disease and increasing animal productivity.
ranges from 1200 m.a.s.l. to 2210 m.a.s.l. and they are located at 08º34'N and 35º59'E.The area is endowed with water bodies like Keto/Hindina, Hokorsa, Lome and Kombolcha and many other tributaries that drain into a large river named the Birbir.According to the Hawa-Gelan District Agricultural

Table 1 .
The overall Glossina species caught per 48 hours in Settlement 21, Tulema and Settlement 17 were 366, 432 and 698, respectively.Fly catch FIGURE 1: Map of the study area, Hawa-Gelan district.FIGURE 2: Mean catch of fly genera (flies per trap per day) per settlement.

TABLE 1 :
Relative abundance of Glossina species and biting flies trapped from three settlement areas.

TABLE 2 :
Proportion of male and female Glossina species.

TABLE 3 :
Occurrence of trypanosome infection in cattle in settlement areas of Hawa-Gelan district.