Immunogenic Properties of Babesial Serum Antigens

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Abstract
The presence of antigens found in the sera of horses, dogs, and rats with acute babesiosis was correlated with the appearance and persistence of parasitemia. Antibodies against these antigens appeared at the time the infections became latent and persisted for at least 14 months. Decreases in antibody titers were acompanied by transitent parasitemia, slight anemia, and recurrence of the antigens in the serum in dogs infected with Babesia canis and horses with mixed Babesia equi-Babesia cabalii infections, and in rats with Babesia rodhaini. Partially purified antigen of rat-acute B. rodhaini-origin. and beta globulin associated antigen, fraction B of dog-B. canis-origin were both shown to stimulate production of protective antibodies in either immunized rats or dogs against challenging infections of B. rodhaini and B. canis respectively. Antigen fraction A, associated with gamma globulin, of dog-B. canis-and all antigens of horse-B. equi-B. caballi-origin stimulated only partial protection in dogs and rats against challenging infections. Antisera produced in rats or dogs against the partially purified antigens of dog and rat origin both passively immunized either dogs against B. canis or rats against B. rodhaini. Antisera produced in rats or dogs against the antigen of horse origin did not give passive protection to either dogs or rats challenged with Babesia parasites. These serum antigens are probably the significant immunizing substances associated with acute babesiosis. They show a remarkable lack of parasite species specificity in both their serologic and im-munogenic properties.