Prevalence and associated risk factors of bovine trypanosomosis in Benatsemay district, SouthOmo zone, Ethiopia

Yimer Muktar, Mesay Asmelash and Negesse Mekonnen¹

Haramaya University, College of Veterinary Medicine P.O.Box 138, Dire Dawa Ethiopia
yimermktr21@gmail.com
¹ National Animal Health Diagnostic and Investigation Center, Sebeta, Ethiopia

Abstract

Cross-sectional study was conducted in Benatsemay district of South Omo zone, Ethiopia, to determine the prevalence of bovine trypanosomosis, and to assess associated risk factors of the disease. Blood samples were collected from 217 randomly selected cattle of the study peasant association (PA’s) and evaluated through standard parasitological and haematological methods.

The overall prevalence of trypanosomosis was 64(29.5%, 95% confidence interval (CI) 23.51-36.04) comprising 36.14%, 26.67% and 24.32% from Kako, Keyafer and Alduba PA’s respectively. The most common trypanosome species identified were T. congolense (67.2%) followed by T. vivax (32.8%). Disparity in the prevalence of trypanosome infection was recorded in the different PA’s and between the two sexes, body condition, skin colour and altitude level but the difference was not statistically significant (p>0.05).However, statistically significant difference (Odds Ratio (OR)=2.36, 95% CI=1.16-4.81, P=0.02) was observed in the prevalence of trypanosomes between the two age groups, with  higher infection rate being recorded in adult (34.44%) than in young(18.18%) animals (P=0.02). Univariable logistic regression analysis showed that anaemic (PCV < 24%) had 5.7 times the risk of being trypanosomosis positive compared with non anaemic animal (> 24) (OR = 5.7, 95%CI2.77-11.77).Statistically significant difference (P= 0.00) was observed with the mean PCV values between aparasitaemic (24.92±0.32SE) and parasitaemic animals (21.94±0.29). In conclusion, this study revealed that trypanosomosis poses a threat to cattle production in Benatsemay district. Hence, appropriate disease prevention and control methods should be implemented to improve livestock production and agricultural development in the area

Key Words: age, anaemia, buffy coat, T. congolense, T.vivax, PCV, sex

Introduction

In countries such as Ethiopia, where livestock is an important part of the agricultural sector, trypanosomiasis contributes to the direct economic losses of crop-livestock production. Animal Trypanosomosis is an important livestock disease in Africa which is considered as a threat to the ongoing effort on poverty alleviation in the continent (Wint et al 2010). It is a serious disease in domestic livestock that causes a significant negative impact in food production and economic growth in many parts of the world (Taylor et al 2007), particularly in sub-Saharan Africa (Cecchi et al 2008).

In Ethiopia animal Trypanosomosis is among of the most important diseases limiting livestock productivity and agricultural development due to its high prevalence in the most arable and fertile land of South West and North West part of the country following the greater river basins of Abay, Omo, Ghibe and Baro, which has a high potential for agricultural development (Shimels et al 2005). Over 6 million heads of cattle and equivalent number of other livestock species are at risk of contracting the diseases. More than 20,000 heads die per annum, and annual loss attributed to the diseases is estimated to be over US$236 million, whereas loss due to reduce meat, milk  and draft power  is not applicable to this figure (OAU 2002).

The tsetse flies are widely distributed in the western southern and south western low lands and river valleys and 15% of the land believed to be suitable for livestock production is affected by one or more of the following species of tsetse flies; Glossina morsitans sub morsitans, G. pallidipes, G. tachinoides, G. Fuscipe sfuscipes and G. longipennis (Abebe 2005). Apart from cyclical transmission of Trypanosomosis by Glossina species, mechanical transmission is a potential threat to livestock productivity in some parts of Ethiopia (Abebe and Jobre 1996). Trypanasoma vivax infection can be transmitted mechanically by several tabanide and large number of biting flies (Chernet et al 2006). Biting flies have been reported as the major cause of T. vivax infection in three highland districts bordering Lake Tana (Sinshaw et al 2006).

The most important trypanosome species affecting livestock in Ethiopia are Trypanosome congolese, Trypanosome vivax and Trypanosome brucei, in cattle, sheep and goats, Trypanosoma evansi in camels and Trypanosoma equiperdium in horses (Abebe 2005). In Ethiopia, few studies were conducted regarding trypanosome prevalence and also few studies were performed in the current study area. Therefore the objectives of the present study were to determine the prevalence of bovine trypanosomosis and to assess the risk factors of the disease together with the identification of species of trypanosomosis in study area.

Materials and methods

Study area description

A study was conducted in three peasant associations (PA’S) of kako, Alduba and keyaferin Benatsemay district of South Omo Zone and its capital, Keyafer is situated 750 km from Adis Abeba and 42 km from South Omo. The geographic coordinate system, Benatsemay.

District covers the area between 5⁰01^’ to 5⁰73N and 36⁰38^’ to 37⁰07^’E. According to the information obtained from Benatsemay  district Agriculture and Rural Development Office (2014), estimated total population of animals the district was 70,640 of which 35,736 were males and 34, 904 are females.  The majority of the population lives in rural areas and practices livestock production as the mainstay of livelihood. Regarding agro climatic zone subdivision, 5% of the total 2922.8 Km² of Benatsemay district land belongs to bereha, 81% falls under kolla and only 13.7% of the district is under woinadega. The mean annual rain fall of the district is 570.5 mm. Recorded data in the district indicated that the daily temperature ranges from 16⁰C to 42⁰C and altitudinal range of 528 to 1645 metres above sea level.

Study population

The study was carried out on 217 indigenous zebu cattle (of all age groups and sexes) in three selected Peasant Associations (PA’s), which are managed under mixed farming system.

Study design and Sample size Determination

The study was a cross-sectional study and samples were collected from November 2014 to April 2015. Animals were randomly selected from three peasant associations (kako, Alduba and keyafer) that were assumed to represent the part of the study area. A total of 217 animals were randomly sampled for the study. The sample size was determined based on sample size determination for prevalence study given by (Thrusfield 2007) from a previously reported prevalence rate of 17% and 95% confidence level, 5 % of desired absolute precession. During sampling sex, age and body condition of animals and skin colour were recorded. The age of the animals was grouped as young (1-3 years) and adults (>3 years) according to the classification used by Ayana 2012. The body condition score was categorized as poor, medium and good taking the middle point as a border in the 9 scale scores of  Nicholson and Butterworth (1986) methodof body condition was scoring for zebu cattle.

Packed Cell Volume (PCV) Determination

Blood samples were obtained by puncturing the marginal ear vein with a lancet and collected directly into a pair of heparinised capillary tubes. The tubes were then sealed at one end with crystal seal. The capillary tubes were placed in micro-hematocrit centrifuge and were allowed to centrifuge at 12,000 revolutions per minute (rpm) for 5 minutes.  After centrifugation, the capillary tubes were placed in a haematocrit reader. The length of the packed red blood cells column is expressed as a percentage of the total volume of blood. Animals with PCV less than 24% were considered to be anaemic (OIE 2008).

Buffy Coat Technique

Heparinised microhaematocrit capillary tubes, containing blood samples were centrifuged for 5 min at 12,000 rpm. After the centrifugation, trypanosomes were usually found in or just above the buffy coat layer. The capillary tube was cut using a diamond tipped pen 1 mm below the buffy coat to include the upper most layers of the red blood cells and 3 mm above to include the plasma. The content of the capillary tube was expressed onto a glass slide, and covered with cover slip. The slide was examined under x40 objective and x10 eye piece for movement of parasite (Paris et al 1982). For the purpose of species identification, a thin blood smear was prepared from the buffy Coat (BC) for those samples that were positive on buffy coat examination and stained with Giemsa stain and examined under a microscope using the oil immersion 100x objectives (Murray et al 1983; MORAD 2007; Radostitis et al 2007).

Data Analysis

Data obtained were stored in Excel spread sheet.The data were analysed by using STATA version 11.0 for window. The association between trypanosome infection and risk factors/variables (age, sex, body condition, origin/PA, skin colour and attitude level) were determined by univariable logistic regression and two sample student t-test was used to compare mean PCV of infected and non-infected animals. A statistically significant difference between variables was considered at P<0.05 at 95% confidence level. PCV was categorized as anaemic if it is less than 24% and normal if it is greater than or equal to 24%.

Results

Parasitological findings

Out of 217 cattle examinedwith a Buffy coat technique, 64 were positive for trypanosomes giving an overall prevalence of 29.49% (95% CI=23.51-36.04).The highest prevalence (36.14%) was observed in Kako while the lowest 24.32% was observed in Alduba PA’s. The association of trypanosomes infection with different potential risk factors as analyzed by univarable logistic regression revealed that there were no significant association between trypanosome infection, and the risk factors analyzed (body condition, skin colour, altitude level and sex of animals). The prevalence was slightly high in male (33.94%) and lowland attitude (31.25%) than female cattle (25.0%) and highland attitude (26.97%) respectively (P>0.05). However, statistically significant association (OR=2.36, 95%CI= 1.16- 4.81, P=0.02) was observed between trypanosome infection and age of the animals (Table 1).

Among the total of 64 cases of trypanosome infections detected, 67.2% were due to T. Congolense and the rest were due toT. vivax (Figure 1).

Figure 1: Distribution of the species of trypanosomes among the infected animals

Haematological finding

Among the anaemic animals 43.9%were positive for trypanosomosis while only 11.7% of non-anaemic animals were positive for trypanosomosis (Table 2). The risk of being anaemic increased by 5.7 fold when animals were infected with trypanosome (Table 2).

The mean PCV of parasitemic animals were lower than that of the aparasitemic ones (Table 3).

Linear regression analysis of PCV and parasitemic cattle confirmed a unit variation/increase in the buffy coat result caused a reduction of the PCV value by 2.98% table 4.

Discussion

The overall prevalence of bovine trypanosomiasis in the study area was found to be 29.9 %.This result was in close agreement with the finding of Abraham and Tesfaheywet (2012) and Terzu (2004) who reported 27.5% and 23% in Arba Minch, Southern Ethiopia and western Ethiopia, Metekel district, respectively. However, the present study was higher than the previous result of Abebayehu et al (2011), Teka et al (2012), Fayisa et al (2015)Ayana et al (2012) and Kumela et al (2016)who reported a prevalence of 2.66%, 4.43%, 4.86%, 2.10% and 4.25%from Western Tigray, Northern Ethiopia,Didesa District, Arbaminch area, Amhara region, Northwest Ethiopian and Ilubabor Zone, Southwestern Ethiopia, receptively. The variation between reports might be due to the difference in management system, season of the study period, the development of drug resistance, and the increase of tsetse challenge due to higher vector density and lack awareness of the animal owners about the disease in the study area.

In this study, two species of trypanosomes mainly T.congolense and T.vivax were identified. Out of the 64 trypanosomes identified, T. congolense accounted for 67.2% while the rest 32.8% was due to T.vivax. Higher prevalence of T. congolense compared to the prevalence of T.vivax was in agreement with previous works of Rowlands et al 1993, Muturi 1999, Afework et al 2001, and Tewolde 2004 who identified T.congolense with prevalence of 84%, 66%, 60.9% and 75% in their study in Ghibe valley, Merab, pawe, and western Ethiopia, respectively.

The reason for the high ratio of T. congolense than T. vivax could be due to the high number of serodems of T. congolense as compared to T. vivax and the development of better immune response to T. vivax by infected animals (D’Ieteren et al 1998; Leak 1999). However, Cherenet et al(2006) reported as T. vivax was responsible for 90.9% of the cattle trypanosome infections in their study in tsetse-free zones of the Amahara region, Northwest Ethiopia while T. congolense and T.vivax contributed almost equally to the trypanosome infections in tsetse infested area. This is due to fact that T.vivax can also be transmitted by mechanical vectors other than tsetse.

Univariable logistic regression analysis of different risk factors (origin of animals /PA’s, sex, body condition, skin colour and altitude level considered during the study did not show any significant association with occurrence of trypanosomosis. On the other hand, the risk of being anaemic increased by 5.7 times (table 2) when cattle are infected by trypanosomosis (P=0.00). Moreover, linear regression analysis of PCV and parasitemic cattle confirmed a unit variation/increase in the buffy coat result caused a reduction of the PCV value by 2.98%, (P=0.00).  Among anaemic cattle 43.9% were diseased with trypanosomosis the current  finding was comparable with the previous results by Afework et al (2001) at Pawe, North West Ethiopia and Muturi (1999) at MerabAbaya, South Ethiopia.

In the current study the prevalence of trypanosome infection did not differ among the peasant associations and this might be due to similar agro-ecology and vectors abundance in all peasant associations. On the other hand, the slight difference among the three PA’s might be attributed to uncontrolled animal movements between peasant associations coupled with favourable environment for the vectors and availability of their preferred hosts, which is not necessarily domestic livestock (Radostits et al 2000) as the area is endowed with different wild animals.

Sex was not a significant predictor of trypanosomeinfection in cattle from Benatsemay district. This finding coincides with the earlier report by Teka et al (2012) and Tamiru et al (2014) who observed no significant difference in susceptibility between sex groups. The possible explanation for this might be both males and females can be affected equally and uniformly in high tsetse challenge areas.

The infection rate of trypanosomosis was slightly higher in poor body condition compared to medium and good body condition cattle’s.  In contrast, 64.18.0% of apparasitaemic cattle were with poor body condition and this indicates that other factors such as diseases, nutritional factors as well as management system may have contributed for the poor body condition of cattle (Smith 2009). The relatively lower rate of trypanosomosis infection in the medium, good body condition animals might be related to that well-nourished animals have good level of immunity and are in a better position to resist infection, moreover there is a very rare possibility of re-establishment of infection in animals with good body condition.

In this research work, age was found to be a risk factor; higher infection rates were observed in adult animals. This is logically associated to the fact that young animals are also naturally protected to some extent by maternal antibodies (Fimmen et al 1992). In addition, adult animals travel and cross-different vegetation types for grazing, watering, as well as for draught and harvesting crops to tsetse high challenged areas. Moreover, previous reports also showed that higher prevalence in adult animals as compared to young animals which is believed to be due to high preference of tsetse for adult animals and less exposure of young animals to tsetse challenge as they are usually kept at homestead (Torr et al 2001; Cherenet et al 2006).

The mean PCV of parasitemic cattle were significantly lower than that of the aparasitemic ones (P=0.00) (Table 3) similar finding were reported by Afework et al (2001), Muturi (1999) Abraham and Zeryehun (2012) and Ayana et al (2012).  Packed cell volume has been demonstrated to be a good indicator of trypanosomal infection (Marcotty et al 2008). The aparasitemic cattle with PCV<24% in the current study might be either due to the low sensitivity of buffy coat techniques in chronic cases of trypanosomiasis or could be due to other factors like poor nutrition  and other diseases particularly parasitic  diseases which cause anaemia (Afework et al 2001; Picozzi et al 2008). Moreover, the present study also revealed that 11.7% of the cattle have a PCV value in the normal range/non anaemic (PCV≥24%) are react positively to trypanosomiasis infection and this might have occurred due to recent infection with trypanosomiasis. This result agree with the previous result of Garoma (2009) who conclude that cattle’s having PCV value of normal range were shown to be infected with trypanosome parasite.

Conclusions

• In this cross-sectional study of trypanosomosis in cattle, an overall prevalence of 29.5% was observed and the high prevalence of the current result confirmed that the continuous threat of trypanosomosis in the study area.The major species of trypanosomes identified were T. congolense followed by T. vivax. According to the host risk factors, the prevalence of bovine trypanosomosis was higher in adult than in young cattle. The mean PCV value of parasitemic animals was significantly lower than that of aparasitemic animals. This indicates that infection with trypanosomosis negatively affects PCV profile of animals, however, PCV alone could not be used as diagnostic  tool because non anaemic/normal animals (11.7%) may also became positive for trypanosomosis infection. Therefore, proper strategies have to be designed and implemented tominimize its effect on livestock production in the studied area.

Acknowledgements

The authors would like to acknowledge WolaitaSodo regional veterinary laboratory for their technical assistance and provision of materials during the field study. We are also grateful to the animal owners for their cooperation during sampling.

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Received 13 October 2016; Accepted 1 November 2016; Published 1 December 2016

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