STRAIN VARIATION LIMITS PROTECTIVE ACTIVITY OF VACCINES BASED ON SOLUBLE BABESIA-CANIS ANTIGENS

Groups of five dogs were immunized with vaccines containing soluble pa rasite antigens (SPA) derived from in vitro culture of Babesis canis p arasites, either obtained commercially (Pirodog(R)) or produced at lab oratory scale. Both vaccines generated antibodies that reacted with pa rasitised erythrocytes (PE). Upon challenge infection with homologous parasites, protection was evident from less severe decreases of haemat ocrit values, and reduced morbidity. Vaccinated animals, however, were not protected against challenge infection with heterologous B. canis parasites. Recovery from challenge infection coincided with the produc tion of antibodies against parasitized erythrocytes. The results sugge st that SPA from B. canis carry strain-specific determinants that are crucial for inducing protection in dogs against challenge infection, a nd explain vaccination failures in the field.