ABSTRACT
Immunity to Babesia infection depends on the innate resistance of the host in addition to specific responsiveness to Babesial antigens. Exoantigen-containing supernatant fluids from Babesia in vitro cultures are now being used as soluble immunogens for vaccination against bovine babesiosis and are efficacious in the induction of heterologous strain immunity in susceptible cattle. The capacity of the host to overcome a Babesial infection is determined not only by specific immunologic responsiveness, but also by certain innate characteristics of the host. Passive transfer of immune serum into susceptible animals has been shown to confer partial protection against Babesia infections, with immunity predominantly species specific. Studies have focused on the role of the natural killer cell in cellular immune responses to Babesia infection. Much of the humoral immune response to both Babesia and Plasmodium spp. is directed against asexual blood stage antigens, particularly against those of the merozoite.
