God has blessed Pakistan with a large population of domestic animals which plays a key role to fulfill the ever-augmenting demand of animal protein and milk production. On the other hand, their roles in draft power for agriculture in the country cannot be ignored. The parasitic problem is a serious constraint for the livestock population in most of the developing and under-developed countries of the world because it causes serious economic impact on the livestock and dairy industry through meat and milk reduction and the cost requires as a control measures.
Bovine theileriosis is a protozoan haemoparasitic disease of wild and domestic population over a wide geographic area of the world caused by different members of genus Theileria. This disease is also known as Mediterranean theileriosis, East coast fever, Mediterranean cost fever, Corridor disease, Theileriasis, African coast fever, January disease and Zimbabwean theileriosis in different reigons of the world with respect to different aspects. In our reigon, it has been described as tropical theileriosis caused by Theileria annulata and influencing livestock industry through disturbing the economic of livestock production in global perspective. In comparison with the buffalo, cattle is more proned to the infection. Among different breeds of cattle, exotic and crossbreds are more affected than indigenous breeds (e.g.Sahiwal). Theileriae requires two hosts for the completion of its life cycle which are ticks (invertebrates) and mammals (vertebrates). Sexual reproduction takes place in ticks while asexual reproduction occurs in both vertebrate and invertebrate hosts. Theileriae infects both erythrocytes (RBCs) and leukocytes in the blood during its life cycle. The higher incidence of Theileriasis in exotic and crossbreds might be associated with the higher susceptibility to the tick vectors. Theileriaannulata has been found to be transmitted through bites of Hyalomma spp. of ticks. Other genera of ticks acting as vectors of Theileriaspp include Dermacentor, Rhipicephalus, and Haemaphysalis ticks. As far as the seasonal prevalence in Pakistan is concerned, the disease remains endemic throughout the year and becomes epidemic during summer and peak level is attained during July and August and then it starts descending till winter season where it becomes sporadic and from March onward disease prevalence increases till the summer reaches.
Clinical symptoms and pathogenesis of theileriosis are related to the multiplication of parasites within transformed lymphoblastoid cells. The infection of T. annulata is characteristic for the lympho-destructive processes. As lymphocytes are the cells which are responsible for the cell mediated immunity against specific pathogens; so, theileriosis badly affects animals immune system. Pathogen also invades and causes destruction of erythrocytes resulting in anaemia. The clinical signs of acute infected animals are enlargement of lymph nodes that drain the site or area of tick infestation, anorexia, high heart frequency, inappetence, weakness, ceasing of rumination, decreased milk production, conjunctivitis, nasal and ocular discharge, lacrimation, diarrhea and hemoglobinuria. Infected animals, that suffer from the peracute form of the disease, may die in 3-4 days after the first symptoms are noticed. In the chronic form, irregular fever, clear emaciation, anemia and icterus may persist for one to two months before the animal recovers to normal. According to a recent study conducted in district Khanewal, grazing, tethering of animals and closed housing are the factors that increase the occurrence of theileriosis. Briefly, all those factors which facilitate the settlement and propagation of tick vectors have been found responsible for increase in the prevalence of theileriosis.
Under the field condition theileriosis can be diagnosed tentively on the basis of clinical signs and tick infestation on the infected animals but it can be confirmed through conventional optical microscopy of Giemsa-stained blood films. Methyl green pyronin stain can be used as a useful tool for the epidemiological study of theileria vector through differential staining the salivary glands of the ticks. The advent of the DNA-based diagnostic techniques such as PCR allowed the detection of piroplasms at low parasitemia. For example, PCR is more sensitive for the detection of Theileria spp. in asymptomatic cattle when compared to microscopy. Other diagnostic techniques which can be used for the diagnosis of theileriosis are Complement Fixation Test (CFT), Reverse Line Blotting (RLB) system, Hybridization techniques, Serological test, IFAT (Immunoflourescent Antibody Technique), Latex Agglutination Test, Enzyme Linked Immunosorbent Assay (ELISA) and Loop Mediated Isothermal Amplification (LAMP).
The treatment of theileriosis is primarily done by using Buparvaquone (Butalex) (2.5mg/kg live body weight I/M). Oxytetracyclin (Resomycin-s, Resomycin LA, Nawacin and Nawacinpvp) (20mg/kg live body weight) can also be used for its treatment. Combination of both Buparvaquone and Oxytetracyclin at their above mentioned recommended dose rates is also effective for the treatment of theileriosis. On the whole Buparvaquoneis more effective as compared to Oxytetracyclin.
Following measures could be taken in order to control/prevent this nuisance:
(i) vector control is the best choice to work out. Farm should be free from any cracks and crevices as these are the best places for the tick hiding.
(ii) Separate housing of exotic and crossbred cattle from buffalo is also helpful in vector control as cattle are more prone to tick infestation than the later.
(iii) Rotational grazing is another useful method in vector control programme.
(iv) In case of small farms, ticks can be removed manually at the time of milking.
(v) Grooming has also been found helpful in vector control.
(vi) Chicken can be used as a biological control through tick predation of chickens for 3-4 hours that will reduce the tick infestation on the animal body.
(vii) Now-a-days most widely used method for tick control is the application of acaricides to the animals which includes cypermethrin, ivermactin, carbamate and amitraz. Acaricides can be used by dipping, washes, spraying, pour-on and or by injections. Dipping is desirable in commercial dairy farming or tick eradication programme. However, in order to avoid from any complications of dipping, it is desirable that the animal should not be thirsty while dipping.
(viii) In different parts of the world, the administration of crude extract of ticks have been proved effective for tick rejection from animals but the level of resistance obtained is far less than required.
(viii) Vaccination of the farm before the onset of season (summer) can be done as preventive therapy. Although no work has been done for its vaccination buta lot of work is in progress for vaccination therapy.
Although, some research has been done about epidemiology and diagnostics of this disease in our country but the importance which should be given to this chapter of veterinary parasitology due to its destructive nature is lacking which has made this disease a nightmare for livestock population in the summer seasons.
The writers are associated with the Department of Parasitology, University of Agriculture, Faisalabad, Pakistan.