Introduction

The donkey is widely distributed through out Ethiopia with an estimated population of 5.2 million (Saul et al., 1997). It is most commonly found in the dry and mountainous areas (Alemu et al., 2004). Majority of the donkeys are found in the central high lands of the country including Arsi, Showa and also northern parts of Ethiopian, with highest density being in Arsi followed by Tigray and Showa. According to the Agricultural sample survey conducted during 2005/2006, the number of donkeys and mules in Tigray Region are estimated to be 387,390 and 7,900, respectively (CSA, 2006).

Despite the increase in mechanization throughout the world, donkeys are still well deserving of the name ‘beasts of burden’ with their inherent ability to thrive in harsh environments (in arid and semi arid areas and where roads are poor or none existent). They are playing an important role in transportation (riding, pack transport or pulling cart), farming (tillage, threshing) and in certain countries they aid in raising water and milling (Pearson et al., 1994; Mwenya and Tandkeib, 2004).

Recurrent drought in Ethiopia resulting in increased cattle mortality has also contributed to an increase in donkey’s usage as draft and pack animal both in rural and urban areas. In general, donkey has a prominent position in the agricultural system of Ethiopia especially to the resource poor communities in rural and urban areas. The low level of development of the road transport network and rough terrain of the country make the donkey the most valuable, appropriate and affordable pack animal under small holder farming system of Ethiopia (Gebreworld et al., 2004). The use of cart donkeys in door to door transport of goods also provides urban dwellers with the opportunity of income generation (Demelash and Moges, 2006).

Despite the number, its prominent role in rural and agricultural life system of the country, the knowledge pertaining to the physiology, nutritional requirement, health problems and management system of the donkey is still limited and rarely available in the literature except the endeavor of the Donkey sanctuary since its establishment.

Even though donkeys have often been described as sturdy animals, they succumb to a variety of infectious and non infectious diseases and a number of other problems (Feseha, 1997). Donkeys harbor several protozoan and metazoan parasites. Among haemoparasitic diseases in donkeys, trypanosomiasis and babesiosis are attributed in reduction in their draughts power efficiency and even their survival (Svendsen, 1997).

In Ethiopia, there are only few published reports about donkey hemoparasites and all the available data are on trypanosomiasis and restricted to only some tsetse infested areas of the country (Kanchula and Abebe, 1997; Assefa and Abebe, 2001; Shelima et al., 2006; Abebe and Wolde, 2010). In this regard well documented information about donkey haemoparasites in most geographical areas of the country is scanty and not strong enough to plan a control strategy. Therefore, the current study was contemplated with the objective of estimating the prevalence of haemoparasites and identifying the associated risk factors in the selected two districts of Tigray regional state, Northern Ethiopia.

Materials and Methods

Study area

Study population

Study design and sampling method

Parasitological and hematological examination

Serological investigation

Statistical analysis

Results

Parasitological findings

From the total of 400 donkeys examined in the two districts, 10 animals were found to be infected with Babesia or Trypanosoma. Therefore, the overall prevalence of haemoparasites was 2.5%. On a genus level, the prevalence was 1.75% for Bebesia and 0.75% for Typanosoma (Table 1). The species of Babesia identified were Babesia equi (71.4%) and Babesia caballi (28.6%) while all the trypanosomes encountered were belong to the single species of Trypanosome vivax (Table 2).

Figure 1

Table 1: Prevalence of haemoparasites in working donkeys in the two study districts

Figure 2

Table 2: and species identified in working donkeys of the study area

The results of statistical analysis of different risk factors with Babesia spp and Trypanosoma vivax infections are given in Table 3 and Table 4, respectively. No significant variations were observed in the prevalence of both Babesia spp and Trypanosoma vivax infections in donkeys between the two study districts (p>0.05). Observation of the BCS of the donkeys showed that from the 400 donkeys examined, 94 (23.5%), 203 (50.75%), and 103 (25.75%) animals were in good, moderate and poor conditions, respectively. Babesia spp were detected in donkeys with moderate and poor BCS whereas Trypanosoma vivax was found only in donkeys with poor BCS. Nevertheless, the association between Babesia spp or Trypanosoma vivax infections and BCS was not found to be significant (p>0.05 in both cases). Age of the animals was not significantly associated with the prevalence of the haemoparasites (p>0.05). All the animals infected with Babesia spp or Trypanosoma vivax were above two years of age. As with other factors, the prevalence of both Babesia spp and Trypanosoma vivax infection was not significantly associated with the sex of the animals (p>0.05).

Hematological findings

The mean PCV value of all donkeys tested was 28.6±5.76%. There was no significant (p>0.05) variation in mean PCV between babesia infected and free animals. In contrast, animals infected with Trypanosome vivax had a significantly (p<0.05) lower mean PCV than those non-infected. Using a PCV value of 30-46% as a normal value (Knottenbelt, 2005), about 90% of parasitaemic and 43.85% of non parasitaemic donkeys were found to be anemic (Table 5).

Figure 3

Table3: Chi-square analysis of different risk factors with spp infection in donkeys

Figure 4

Table 4. Chi-square analysis of different risk factors with infection in donkeys

Figure 5

Table 5: Analysis of the association between haemoparasites and mean PCV in donkeys using t-test

Serological analysis

Discussion

The prevalence of both Babesia spp (1.75%) and Trypanosoma vivax (0.75%) infection observed in this study is generally very low when compared with previous reports from different parts of the country. The prevalence of babesiosis in donkeys was reported to be 10.3% in a previous study conducted in three different areas of Central Showa (Kebere, 1998, unpublished). On the other hand, previous studies of donkey trypanosomosis have reported a prevalence of 12 - 21% in north Omo Zone (Yimam, 1993, unpublished; Kanchula and Abebe, 1997; Assefa and Getachew, 2001), 28.5% in Humbo, Wolayita zone (Shelima et al., 2006) and 6.3% in Northwest Ethiopia (Abebe and Wolde, 2010). The observed difference in prevalence between the present and previous studies might be associated with the better veterinary services provided in the area by the Tigray DHWP with babesiocidal and trypanocidal drugs. Secondly, it could also be due the study design employed as a cross-sectional study depicts only a specific period of the infection status in the animals examined. The diagnostic capability of the parasitological technique used might be another possible reason. The traditional light-microscopic examination of thin blood smears can be difficult in the case of carrier animals where presence of parasites is scant, and even in acute cases at the onset of the disease (Nagore et al., 2004). The low prevalence of haemoparasites in this study might also be associated with the season of study. The current study was carried out from November 2009 to March 2010, a period known to be dry in Ethiopia. A previous trypanosomosis study in the country has shown seasonal variations in the prevalence of Trypansoma vivax infection with values higher between June and November (rainy season) than in the other months correlated with biting fly density (Rowlands et al., 2001). Similarly, Sinshaw et al. (2006) have recorded a high population density of biting flies in the rainy season than in the dry and stated that biting flies require a wet habitat for multiplication and larval growth.

Trypanosoma vivax was the only trypanosome species identified in the current study. This species was differentiated based on the morphological features described by Uilenberg (1998) as follows. The parasite had a free flagellum. Its length, including the free flagellum, varied from 18 to 26 μm. The kinetoplast was large and terminal. The nucleus was centrally placed, but the bulk of the cytoplasm was found in the posterior part. The posterior extremity was swollen and blunt and the undulating membrane was inconspicuous. Since the study area is known to be tsetse-free, the occurrence of this species could be due mechanical transmission by biting flies. It has been established that in the absence of appropriate tsetse flies, Trypanosoma vivax can be transmitted mechanically between infected and susceptible donkeys (Radostits et al., 2007). The present finding is consistent with that of a previous study (Addisu, 2009, unpublished) in which Trypanosoma vivax was detected to be the only species in a district where tsetse flies were not caught. This parasite has also been reported as the predominant species even in the tsetse infested areas of the country (Yimam, 1993, unpublished; Kanchula and Abebe, 1997).

With respect to Babesia, a greater proportion of donkeys were infected with Babesia equi (71.4%) than Babesia caballi (28.6%). This finding is in agreement with a previous study (Nuria, 1992, unpublished) reporting Babesia equi (86.2%) as a widely distributed species than Babesia caballi (13.8%) in Bahir dar and its surroundings. Babesia equi infection in donkeys has also been reported from other tropical and subtropical countries like India, Brazil and Arabian countries (Kumar et al., 2002). The present finding is also inline with Soulsby (1982) stating that Babesia equi has a possibly much wider distribution than Babesia caballi. Contrary to the current finding, the predominance of Babesia caballi over Babesia equi has been reported in Turkey (Acici et al., 2008). Babesia equi is known to be more virulent and tends to cause a fulminating parasitaemia (Gerstenberg et al., 1998).

Ixodid ticks of the genera Hyalomma, Dermacentor and Rhipicephalus have been identified as vectors for the transmission of either Babesia equi or Babesia caballi protozoa to natural host (Soulsby, 1982). However, Boophilus species were the most common ticks frequently encountered on the body of donkeys in the current study. This is consistent with a previous study (Feseha, 1993, unpublished) in which Rhipicephalus and Boophilus species were reported to be the major vectors of equine babesiosis in the specific zone.

In agreement with previous studies (Addisu, 2009, unpublished; Abebe and Wolde, 2010), age and sex of the animals did not have significant influence on the prevalence of haemoparasites. Similarly, no significant variation was found in the prevalence of both Babesia spp and Trypanosoma vivax infection between the two districts covered by the study. This could be due to similar agro-ecological conditions and equal veterinary attention given by the Tigray DHWP for the two sites.

The mean PCV of Trypanosoma vivax infected donkeys was significantly lower than non-infected ones. The detection of anemia (indicated by a lowered PCV) in infected donkeys in this study is in agreement with other studies of donkey trypanosomosis (Dhollander et al., 2006; Shelima et al., 2006; Pinchbeck et al., 2008; Abebe and Wolde, 2010). However, the difference in mean PCV between Babesia infected and free donkeys was not statistically significant and this is in agreement with the report of Kebere (1998, unpublished). Using the PCV value range 30-46% as a normal (Knottenbelt, 2005), 43.85% of Trypanosoma vivax free donkeys were found to be anemic. The degree of anemia observed in non-infected animals could possibly be attributed to the compound effects of poor nutrition and concurrent helminthes infection.

Although the number of samples used was small, the serological study revealed that 22% sampled donkeys were seropositive for Trypanosoma equiperdum and Trypanosoma evansi. Lack of sufficient serological kit was the limiting factor to test large number of donkeys. This serological test (CATT/Trypanosoma evansi) uses a standard antigen and proved to be a good test for equine trypanosomosis, whether the causative agent is Trypanosoma evansi (surra) or Trypanosoma equiperdem (dourine) (Claes et al., 2003). Microscopic examination has a low sensitivity particularly for the detection of Trypanosoma equiperdum, which is considered to be a tissue parasite rather than a blood parasite (Burn et al., 1998).

In conclusion, this study has revealed the existence of both Babesia spp (Babesia equi and Babesia caballi) and Trypanosoma vivax in donkeys in the study area. The detection of Trypanosoma evansi and Trypanosoma equiperdum antibodies in the blood of serologically tested donkeys is also of note. The prevalence of haemoparasites observed in the current study is generally low. However, the study design used, season of the study and the low sensitivity of the parasitological test employed should be considered in drawing conclusions from this work. Therefore, a further study using more sensitive tests in combination with vector survey need to be conducted in different seasons and agro ecological zones in order to generate more complete data on the epidemiology of donkey haemoparasites in the Tigray regional state.

Acknowledgement

The Tigray Donkey Health and Welfare Project staff members are duly acknowledged for their technical and financial support.