Some studies on Theileria Annulata with special reference to an attenuated vaccine

The disease, tropical theileriosis, caused by the protozoan parasite Theilerla annulata is assuming greater importance in many tropical and sub-tropical countries because of the improvement in the breeds and productivity of cattle in these countries. Methods of control of the disease are inadequate and a suitable means of immunization would be of great value to the respective livestock industries. The literature dealing with these aspects of the disease relevant to its importance and methods of control is reviewed. Methods of immunization are considered and work is described on the isolation, cultivation, attenuation and use of strains of the parasite. Special attention is paid to the medium used for growing the infected lymphoid cells and the factors contributing to optimum, satisfactory growth. The research described is concentrated on the preparation of vaccines attenuated in tissue culture. Details of the methods of adaptation to and attenuation in, tissue culture of strains of T.annulata. and experiments leading to the development, preservation and use of a definitive vaccine are described, The initial assessment of possible vaccinal value is based on the clinical and haematological response of susceptible bovine animals and the definitive vaccine used is an attenuated strain, initially isolated in Iran. This strain is investigated in respect of its safety in use, its properties as a field vaccine, its ability to withstand deep frozen storage and its immunogenic characteristics. It is shown that the vaccine can "be stored at -70°C. very satisfactorily using glycerol or dimethyl sulphoxide as cryoprotectants, that it is effective when administered subcutaneously and that it causes a readily detectable reaction in susceptible cattle, producing schizonts but not erythrocytic forms; and that' it engenders immunity to a heterologous strain of the parasite. Experiments are described in which an immunity is shown to be produced in cattle which is strong at 1+ months when challenged by a local heterologous strain and still exists, but at a lower level, 12 months after vaccination. Attenuation of T.annulata strains in tissue culture is discussed and a regimen for vaccination of calves and particular care that should be taken for vaccination of adult cattle are suggested. Some suggestions far future investigations are made.