Vaccination of calves with an attenuated cell line of Theileria annulata and the sporozoite antigen SPAG-1 produces a synergistic effect

The sporozoite surface antigen, SPAG-1 and the attenuated schizont infected Tunisian line CL1 of Theileria annulata have been shown, in previous studies, to induce variable levels of protection against homologous and heterologous sporozoite challenge, respectively. We report here the result of a vaccination trial comparing the protection level induced by the SPAG-1 antigen (as a recombinant full length His tagged protein) and the attenuated cell line, used singly or in combination. The results, after challenge of immunised calves with a lethal dose of sporozoites, show that SPAG-1 provides limited protection (one out of seven calves surviving), while the attenuated cell line provides moderate protection (three out of seven calves recovered). The combination of SPAG-1 and the attenuated cell line induced the best protection as indicated by the survival of all the vaccinated calves. These results, together with a range of parasitological and clinical parameters, demonstrate the enhanced protection provided by combining sporozoite and schizont antigens in vaccination against tropical theileriosis.