Introduction

It is well known that the one humped camel (Camelus dromedarii) is an important livestock species uniquely adapted to hot and arid environments more than any other domestic animal. Camels are most numerous in the arid areas of Africa, particularly in Eastern Africa, i.e. Somalia, Sudan, Ethiopia, Kenya and Djibouti. Approximately 11.5 million camels occur in this region and represent over 80% of the African and two thirds of the world’s camel population (Schwartz and Dioli, 1992). In Ethiopia, approximately 1.6 million camels are found in south, southeastern, northeast and western parts of the country, and about 100,000 in the study area (IGAAD, 1989). Camel plays a significant multi-purpose role in dry lands of about 630,000 sq.km. (50% of the total area) of Ethiopia, providing livelihood to over 2 million pastoralists such as Afars, Somalis, Gabras and Boranas. The commonest use of camels by pastoralists in the study area is for transporting grain, water, salt and other goods and for milk production. They are very reliable milk producers even during the dry season and drought years when milk from cattle, sheep and goats is scarce. Inspire of the camel’s importance, few studies on their diseases and husbandry have been conducted. Although ticks and tick-borne diseases (T&TBDs) are common ectoparasites of camels,no comprehensive studies have been conducted and only limited information is available in the literature ( Hill, 1982 ; Nicholson 1985). Apart from disease transmission, ticks cause mechanical damage eg. irritation, ticks worry, anaemia and weight loss (Hill, 1982 ; Nicholson 1985). They are therefore considered a major threat to animal health and milk production. The objective of this study was therefore to investigate the prevalence of different tick species on camels in the arid and semiarid region of southern rangelands of Ethiopia as well as to record other ecto-and endo-parasites associated with camels in the study area.

Description of Climate and Vegetation of the Study Area

The region is dominated by a semi-arid climate. Annual mean temperature vary from 19 to 42^oC with little seasonal variation. The average annual rainfall varies from 440 to 1100 mm, with an average precipitation around 600 mm per annum. The main rain occurs from March-May with an erratic short rainy season from September to early November. The remaining months receives trace or no rain at all. The region is dominated by Savannah vegetation containing mixtures of perennial herbaceous and woody vegetation, mainly of acacia species and thorny shrubs. Several native species of grasses and woody plants provide excellent forage, which have been described by Coppock (1994). The region is important as a source of animal for local consumption as well as export.

Materials and Methods

Adult ticks were collected from a total of 510 camels from different herds belonging to southern rangeland pastoralists, residing in different locations of Teltele, Yabelo, Mega, Arero and Moyale districts and from other camels travelling within the southern regions of Ethiopia, some from neighbouring countries, for a period of 12 months. Tick collection was done monthly from eyelids, ears, nostrils, perianal regions, and tails in labelled universal bottles containing 70% ethanol. Identification was carried out within 5 days of collection using the tick identification keys (Hoogstraal, 1956; Matthysee and Colbo, 1987 and Kaiser, 1987). In addition to ticks, other common biting flies were also collected and identified using the taxonomic keys of Davies (1988) and Kettle (1990).Blood samples were collected from 320 camels from jugular veins in vacuum tubes containing anti-coagulant (EDTA) for blood films and animal inoculation. Giemsa-stained blood films were prepared immediately whereas BALB/c mice were inoculated with 1 ml of blood subcutaneously within 2-3 hr of collection. Two mice were used for each blood sample.

Data Analysis

Analysis of variance (Anova) was used to test levels of significance in tick counts and prevalence of trypanosomosis cases.

Results

In this study, a total of 24,096 ticks representing 11 species were collected from camels (Tables 1 and 2). Out of all the tick species collected, only five were found to be abundant. These are Rhipicephalus pulchellus (59.03%), Hyalomma dromedarii (21.18%), Amblyomma gemma (12.52%), Hyalomma marginatum rufipes (3.49) and Hyalomma truncatum (2.8%). Thus R. pulchellus and H. dromedarii were the most prevalent tick species on camels in the area, followed by A. gemma; H.m.rufipes and H. truncatum. Other tick species collected in small (1.15%) numbers from camels were Rhipicephalus simus, R. evertsi; R. pravus; R. sanguineus and Amblyomma variegatum.

Table 1: Tick species and their relative abundance

Table 2: Tick distribution in study areas

Table – 3 presents the tick species composition at four different attachment sites. H. dromedarii was found all over the body but mainly in the nostrils. H. m. rufipes, H. truncatum, R. pulchellus and A. gemma were found in the perineal (inguinal) region and on switch of tails. R. sanguineus was found mainly around the eyes and ears. R. pravus was found in very small number around the nose and ears. A. variegatum and A. lepidum were found around the inguinal area and R. e. evertsi in the perineal area.

Table 3: Preferred tick attachment sites

Table – 4 shows the ratio of males to females for the main tick species collected during the study period. The results indicate a higher ratio of males to females, especially in the Hyalomma group. T. evansi was detected in camels brought by the owners to veterinary clinics in almost all the study sites. The overall prevalence of T. evansi was 45.9% (147 out of 320 examined).

Table 4: Sex ratios of ticks collected from camels in the study area

Clinically ill animals were found to be positive by both thin and thick blood smears as well as by mice inoculations. The latter method revealed greater numbers of positive cases. In addition to T. evansi 5 camels were found to be infected with other trypanosomes, 3 with T. congolense and 2 with T. brucei. Theileria like organisms were also occasionally observed in the blood smears. Some of the biting flies collected during the study period from the study area were Hippobosca camelina, Phololiche zonata, Pangonia zonata walker and P. magretti Bezzi and Chrysops and Haemotopota spp.

Discussion

In this study, 11 species of ticks were identified on camels, although only five were found in high numbers. In addition to being the most prevalent tick species on camels, R. pulchellus has also been reported to be the most common and abundant tick species on cattle at Didtuyura ranch (Solomon et al., 1998). The common ticks of camels are adapted to the warm climate and their development is greatly influenced by the ambient temperature. Preliminary observation on tick population dynamics on camels indicated that the highest numbers of ticks on animals occurred at the peak of the dry season before the onset of rains.

Immediately after the rainy season, there was a marked decrease in tick burdens. Like all nomads, most camel-owning tribes (Boran, Gabra and Somali) pastoralists move continuously from place to place seeking water and grazing land. The frequency and intensity of camel contact with cattle is likely to influence the presence and abundance of Rhipicephalus and Amblyomma tick species on camels.

The predilection sites of ticks on camels appear some how different from those of other livestock species, perhaps due to differences in their anatomical and feeding habits. For instance, H. dromedarii was collected from all over the body with highest numbers in the nostrils. During high tick infestation season, over 100 ticks per nostril were collected from an adult camel. This information is important for camel tick control since such a site may not be reached by acaricides. Particular attention therefore must be given to this tick species and examination of the immature stages, because the nymphs were also commonly found hiding in the body parts having longer hairs, such as withers, neck, shoulders, hump and ribs areas. The Amblyomma, Hyalomma and some Rhipicephalus species were mostly collected from the inguinal/perineal regions of the animals.

The importance of tick transmitted pathogenic organisms in camels has not yet been thoroughly investigated, although some tick-borne diseases have been reported in the literature (Poccock, 1988). Although ticks are common on camels in Ethiopia in general and particularly in the study area no TBDs were observed except the Theileria like organisms which were occasionally observed in blood smears. The present study has revealed that camel trypanosomosis, especially due to T. evansi, occurs in most parts of the study areas, although the prevalence varies from one place to another. Transmission of these trypanosomes is likely to be through mechanical method by biting flies such as Stomoxys calcitrans, Hippobosca camelina, Philoliche zonata and some species of Pangoniae found in the study area. Disease outbreaks of mechanically transmitted trypanosomoses show a seasonal pattern associated with increasing numbers of biting flies during the rainy season or shortly thereafter, as earlier reported by Dioli and Stimmelmyr (1992). In a study conducted around yabelo area, out of 55 blood samples examined (wet blood films and blood smears), 31% were found to be positive for T. evansi (Tesfaye, 1996). Richard (1979) also reported 12.5% T. evansi infection in camels in Borana province and 21.54% prevalence was later reported in the whole of Borana administrative region (Ketema, 1990). Although T. congolense and T. brucei were identified on morphological basis from the blood smears of sick camels, these species of Trypanosomes were rare in the study areas. The parasites might have been picked up by camels traveling eastwards along the Dawa river and west to the Sagan river to browse in the tsetse-infested gallery forests during the dry season.

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