Determination of the genetypic level of protectiveness in animals vaccined against Theileria annulata

Tropical theileriosis, caused by the protozoan parasite Theileria annulata, transmitted by several species of Ixodid ticks of the genus Hyalomma, is an economically important bovine disease. It is widespread in North Africa, Southern Europe, India, the Middle East and Asia and 200 million cattle are estimated at risk. The disease imposes serious constraints upon both breed improvement programmes and livestock production. Losses which can be directly attributed to tropical theileriosis include mortality, production losses on top of costs associated with veterinary diagnosis/treatment and tick control. Sexual recombination occurring in natural parasite populations plays a significant role in generating genetic diversity. Pharmaceutical applications for treatment and protective vaccination, which make selective pressure on T.annulata populations, can alter the population structure of the parasite and, after transmission to ticks, can cause genetic diversity in the new population. In future, this can give rise to new risk factors (such as drug resistance, reduced vaccine protection, occurance of highly pathogenic isolates) due to altered parasite populations. In this study; protective effect of vaccine at genotypic level and genotipic diversity of non preventive isolates in vaccinated animals, was investigated. For this purpose, blood samples collected from animals vaccinated by attenuated cell line of T.annulata (Ankara) isolate (TeylovacTM, Vetal) during certain periods of time were processed and analysed using polymorphic markers in order to determine protective effect of the vaccine at genotypic level and genotipic diversity of non preventive isolates in vaccinated animals. During field studies routinly carried out by our department in every disease season, it was reported that animals vaccinated with attenuated cell line of T.annulata (Ankara) isolate (TEYLOVACTM, Vetal) were not fully protected against heterologuos isolates of the parasite and vaccinated animals suffered from severe tehileriosis and some were died in Akçaova-Çine region. Based on these data, Akçaova town of Aydın was selected to investigate the effectiveness of the vaccination in this study. As a result, protective effect of vaccine at genotypic level and genotipic diversity of non preventive isolates in vaccinated animals were investigated. Obtained results indicated that risk factors associated with the population dynamics of T.annulata in the fields should be considered. Also, for the effective control of the disease population dynamics, genotipic diveristy and transmission rates of the parasite, animal movements and the proportion of susceptible animals to carriers in that region needs to be determined before vaccinating animals. This obtained data will contribute to development of more effective vaccine control programs against tropical theiloriosis.