Reduced infectivity of Theileria annulata in ticks fed on calves immunized by purified tick antigen

Three cross bred calves were made resistant to Hyalomma anatolicum anatolicum ticks by immunizing with an afrmity purified larval antigen. These three calves together with three non-immunized calves were inoculated with stabilate of Theileria annulata. Very low erythrocytic parasitaemia resulted in all the calves. Hundred forty nymphs were then released on each of the calves. Theileria sp. free immunity against ticks was manifested in calves as impairment of feeding and reproductive performances in nymphs used in challenge infestation. A partial loss of infectivity of sporozoites of T. annulata, harvested from ticks fed on tickresistant calves was recorded in in vitro infectivity test to bovine mononuclear cells.