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 in vitro culture in combination with saponin as adjuvant. Protection against 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 response 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 activity, indicating that a parasite component was responsible for protection. Unlike the malaria situation, disease was not associated with elevated levels of tumour necrosis factor in the plasma, nor with hypoglycaemia. Disease appeared to be the result of the activity of a parasite product, which could have triggered reactions which led to sequestration of erythrocytes from the peripheral venous blood. As a result, the packed cell volume decreased, and organs such as lymph nodes and spleen became congested. As soon as immunity had developed there was a rapid increase in the peripheral erythrocyte number, and congestion of the spleen diminished, indicative of restored capillary blood flow. The results further suggest that vaccination with a soluble parasite product blocks the trigger of this pathological process.