Ticks are within a member called the phylum (Arthropoda), class (Arachnida), sub class (Acari) and Order (Parasitiformes) [16] . Within the Parasitiformes, ticks belong to the suborder Ixodida, which contains a single super family, the Ixodoidea, which is divided into two major families, Argasidae (soft ticks) and Ixodidae (hard ticks), and the rare family Nuttalliellidae, with a single African species [17] . The family Ixodidae, or hard ticks, contains some 683 species [18] . As adults, Ixodids exhibit prominent sexual dimorphism: the scutum covers the entire dorsum in males, but in females (and immatures) the scutum is reduced to a small podonotal shield behind the capitulum, thereby permitting great distention of the idiosomal integument during feeding [19] .

Ixodidae ticks are relatively large and comprise thirteen genera. Seven of these genera contain species of veterinary and medical importance: Amblyomma, sub genus Rhi. (Boophilus), Rhipicephalus, Haemaphysalis, Hyalomma, Dermacentor and Ixodes [17] .

The family Argasidae, or soft ticks, consists of about 185 species worldwide and have one important genus that infests cattle, Ornithodoros [20] . Adult argasids lack a dorsal sclerotized plate or scutum, their integument is leathery and wrinkled, their mouthparts are not visible from above, and they show no obvious sexual dimorphism. Argasidae are wandering ticks, which only remain on their host while feeding [21] .

Mating in the hard ticks takes place on the host, except with Ixodes where it may also occur when the ticks are still on the vegetation. Male ticks remain on the host and will attempt to mate with many females whilst they are feeding. They transfer a sac of sperm (spermatheca) to the female. The females mate only once, before they are ready to engorge fully with blood. When they finally engorge they detach from the host and have enough sperm stored to fertilize all their eggs. Female hard ticks lay many eggs (2000 to 20,000) in a single batch. Female argasid ticks lay repeated small batches of eggs. Eggs of all ticks are laid in the physical environment, never on the host [23] .

Members of the family Ixodidae undergo either one-host, two-host or three-host life cycles. During the one-host life cycle, ticks remain on the same host for the larval, nymphal and adult stages, only leaving the host prior to laying eggs. During the two-host life cycle, the tick molts from larva to nymph on the first host, but will leave the host between the nymphal and adult stages. The second host may be the same individual as the first host, the same species, or even a second species. Most ticks of public health importance undergo the three-host life cycle. The three hosts are not always the same species, but may be the same species, or even the same individual, depending on host availability for the tick. Argasid ticks have two or more nymphal stages, each requiring a blood meal from a host. Unlike the Ixodidae ticks, which stay attached to their hosts for up to several days while feeding, argasid ticks are adapted to feeding rapidly (about an hour) and then promptly leaving the host [12] .

All feedings of ticks at each stage of the life cycle are parasitic. For feeding, they use a combination of cutting mouthparts for penetrating the skin and often an adhesive (cement) secreted from the saliva for attachment. The ticks feed on the blood and lymph released into this lesion. All ticks orient to potential hosts in response to products of respiration [24] . Important Ixodidae ticks that feed on cattle according to the number of hosts required to complete life cycle are listed on table 1.

Currently tick control depends largely on the use of different chemicals. But the development of resistance against commonly available acaricides has created problem in this regard and animal population is becoming

Source: [25] .

susceptible to both the ticks and diseases they transmit, with disastrous outcomes [26] . Resistance of cattle to tick infestation was reported to consist of innate and acquired components. The defense mechanisms, including tick avoidance, grooming, skin characteristics and more specific immunological responses, are involved in reducing the number of ticks parasitizing cattle. Avoidance was attributed to the sighting of the ticks [19] . Spontaneous or acquired resistance may be following infestations, due to the development of cutaneous hypersensitivity. The mechanism responsible for acquired resistance to ticks has been suggested to be a mast cell-depen- dent eosinophil hypersensitivity [27] . Resistance can be passively transferred with viable lymph node cells but not with serum from resistant hosts. This passage method of tick resistance suggests a delayed hypersensitivity mechanism for the acquisition of resistance [28] . The blood histamine level have been found to be elevated as a result of cutaneous basophiles or mast cells increase in resistant hosts, which degranulate in the region of ticks attachment to produce histamine. The histamine has shown to stimulate detachment of tick larvae. But the infestation rate increases in normally resistant zebus either due to true inhibition by the allergic, or by reduced cutaneous pruritis that halts licking that enables to kill the larvae by resistant cattle [26] .

It has been recognized that various breeds of cattle differ in their response to tick infestations. Bos indicus pure breeds and crossbreeds were reported to be more innately resistant than Bos taurus breeds [27] ). According to the observation of authors, African cattle (Bos indicus) naturally self-groom and groom each other frequently and thoroughly. Significantly fewer ticks were found on those animals that were able to groom. Some breeds have the ability to reduce the number of ticks they carry and are considered resistant while others cannot control the number of ticks they carry and thus are referred to as sensitive breeds [20] . A number of physiological and environmental factors can affect the level of host resistance to ticks or the expression of host resistance. Among which nutrition, sex, pregnancy, lactation, age, exposure to ticks, breed and tick density play key roles [29] . Cattle lose resistance with time, and it seems that the older the animal, the lower the resistance. Pregnant cows were significantly more sensitive than non-pregnant female and carried a higher number of ticks mainly during the late stages of the pregnancy. The stress of lactation causes a marked decline in the resistance of exotic breeds; it also affect Zebu, but to a much smaller extent. Stable resistance is acquired after several months of exposure to the species of tick to which resistance is required [27] .

Direct effects of ticks on cattle are tick worry, blood loss, damage to hides and skins of animals and introduction of toxins [11] . The ecology and physiology of ticks have made them second most important vectors after mosquitoes. Ticks transmit a large variety of intercellular bacteria in the Rickettsia group like Rickettsia, Ehrlichia and Anaplasma. Similarly several piroplasm protozoa like T. annulata, T. parva and Babesiosis bigemmina are also transmitted specifically by ticks. Hard ticks (Acari: Ixodidae) are obligate hematophaguos ectoparasites and important vectors of viruses, bacteria and protozoa. They are considered second only to mosquitoes as the most medically important group of arthropods [24] . Tick worry is a generalized state of unease and irritability of cattle severely infested with ticks, often leading to serious loss of energy and weight. This negative effect on the growth of animals and their production is thought to be due to the effects of a toxin in the saliva of ticks [11] .

Anaemia is another inevitable consequence of heavy infestation by any blood-feeding parasite, and cattle deaths attributable to anaemia as a result of tick infestation are common [28] . Engorging Ixodidae females will increase their weight by 100 - 200 times but the actual amount of blood ingested is much greater than this, as blood meal is concentrated and fluid excreted in saliva. Estimates of the amount of blood removed vary according to the species under consideration [11] . Tick saliva contains toxins which have a specific pathogenic effect. The toxins affect not only the attachment site but also the entire organs of the host. Some ticks produce neurotropic toxins which induce tick paralysis that is characterized by an acute ascending flaccid motor paralysis. Females of the species Hyalomma truncatum produce a dermotropic (epitheliotropic) toxin which causes sweating sickness in calves and some adult cattle [31] .

The aim of tick control campaign is not to control all ticks simultaneously, but a definite species because of its particular role [29] . The successful implementation of rational and sustainable tick control programmes in grazing animals is dependent upon a sound knowledge of the ecology or epidemiology of the tick as it interacts with the host in specific climatic, management and production environments. In most situations, however, efficient and reliable methods for the control of cattle ticks and TBD are based on the use of a chemical treatment (acaricide application), often without a local understanding of appropriate ecology or epidemiology [32] .

The availability of each of these options, their advantages and disadvantages, and the cost benefit of each alternative strategy should be assessed before deciding on a control programme [32] . Ideally, strategies should target the parasitic and free-living phases of the life cycle and the role of the ticks in the transmission of TBDs should not be neglected [13] . It is now generally understood that tick control should not only be based on acaricide use, despite the fact that this remains the most efficient and reliable single method. Complementary approaches have been developed and are being researched to enable integrated control strategies against the tick and its haemoparasites [25] [32] . The following are the most commonly used tick control methods.

The distribution and abundance of tick species infesting domestic ruminants in Ethiopia vary greatly from one area to another area [38] . In Ethiopia, studies on tick fauna have begun early in the 19^th century. Since then, different researchers from abroad and country determine the pattern of ticks and the TBDs; and ticks are common in all agro-ecological zones of the country [39] [40] . The main tick genera found in domestic animals of Ethiopia are Amblyomma, Hyalomma, Rhipicephalus, Haemaphysalis and Rhipicephalus [38] .

Among the genera Rhipicephalus, Rhipicephalus lunulatus species were observed in Central Ethiopia [41] , and Rhipicephalus muhasmae in Borena [42] , in wetter western areas of the country [39] [43] . [44] has recorded Rh. humoralis, Rh. cliffordi, Rh. compositus and Rh. distinctus in Wollo and Northeast areas. Rhipicephalus evertsi evertsi, “Red-legged tick” [12] is the most widespread species of Rhipicephalus [45] [46] . Rhipicephalus pulchellus, “Zebra tick” [12] is distributed widely in the north eastern [44] , eastern [47] and southern rangel [46] , part of the country. Rhipicephalus simus, “Glossy tick” [12] , are found in northern [45] , eastern [47] , central [41] .

Of the genus Amblyomma four species that commonly infest cattle includes Amblyomma variegatum, A. gemma, A. lepidum and A. cohaerens and are known to exist in Ethiopia [48] . [42] in Borena zone showed that A. variegatum, A.gemma and A. lepidum distributed in wider area of southern Ethiopia. From the studies of [49] in Jimma A. variegatum and A. coherense are widely distributed in south western Ethiopia. Amblyomma variegatum and A. cohaerens are the two most prevalent Amblyomma speciesin Awassa areas in decreasing order [50] . In eastern Ethiopia, A.variegatum and A. gemma are the two most widely spread species [51] . Amblyomma gemma, “Gem-like bont tick” [52] , is recorded in eastern and southern Ethiopia [39] [43] . Ambylomma varie- gatum and Ambylomma coherence in was also recorded in Haramaya [53] . It is clearly associated with dry types of vegetation or semi-arid rangelands [39] . Amblyomma lepidum, “East African bont tick” [52] , is most commonly inhabits arid habitats and in open bushed shrub or wooded grassland and its distributions overlap with Ambylomma gemma and that of Ambylomma variegatum [12] .

Two species of Rhipicephalus (Boophilus) sub genus are known to exist in Ethiopia, which include Rhipicephalus (Boophilus) decoloratus and Rhipicephalus (Boophilus) annulatus. The study done by [42] in Borena zone; [41] in central Ethiopia; [54] in Asella; [50] in Awassa; [44] in Asella; [55] in Wollo and Asosa area [56] indicated the distribution of Rhipicephalus (Boophilus) decoloratus. Rhipicephalus (Boophilus) annulatus is known to present in Gambella region and recorded by [39] [43] . In Ethiopia, about eight species of Hyalomma that affect cattle are identified, which includes Hyalomma marginatum rufipes, Hy. dromedarii, Hy. tuncatum, Hy. m. marginatum, Hy. impelatum, Hy. anatolicum excavatum, Hy. anatolicum anatolicum and Hy. albiparmatum [53] .