VACCINATION OF DOGS AGAINST BABESIA-CANIS INFECTION USING ANTIGENS FROM CULTURE SUPERNATANTS WITH EMPHASIS ON CLINICAL BABESIOSIS

Groups of five dogs were vaccinated with Babesia canis antigens from i n vitro culture in combination with saponin as adjuvant. Protection ag ainst challenge infection was evident as diminished clinical disease, decrease in parasitaemia, and a less marked fall in haematocrit values . Recovery from infection occurred at the time a memory immune respons e became effective (from Days 5 to 6 after challenge infection onwards ). The effect was dose dependent, the highest antigen dose being most effective. A lysate of normal erythrocytes did not have protective act ivity, indicating that a parasite component was responsible for protec tion. Unlike the malaria situation, disease was not associated with el evated levels of tumour necrosis factor in the plasma, nor with hypogl ycaemia. Disease appeared to be the result of the activity of a parasi te product, which could have triggered reactions which led to sequestr ation of erythrocytes from the peripheral venous blood. As a result, t he packed cell volume decreased, and organs such as lymph nodes and sp leen became congested. As soon as immunity had developed there was a r apid increase in the peripheral erythrocyte number, and congestion of the spleen diminished, indicative of restored capillary blood flow. Th e results further suggest that vaccination with a soluble parasite pro duct blocks the trigger of this pathological process.