The most protective T. parva sporozoite antigen identified to date is the surface protein, p67. p67 is recognized by neutralizing antibodies detected in immunized animals with T. parva sporozoites. Moreover, immunized mice with T. parva sporozoites produced neutralizing monoclonal antibodies and most of these antibodies recognized p67 on the sporozoites surface. p67 is essential for host cell recognition and sporozoite entry, and its expression is strictly limited to the sporozoite stage while the kinete, schizont, merozoite, and piroplasm stages of the parasite do not express p67.