Evaluation of the immunogenic activity of a vaccine for the prophylaxis of bovine anaplasmosis

Abstract

The aims of this work were to formulate a cryopreserved vaccine for the prevention of anaplasmosis and to evaluate its immunogenic activity. A monovalent vaccine of 2.5x107 bovine erythrocytes infected with Anaplasma centrale in a dose of 0.5 ml, cryopreserved in glicerol, was used. Twenty calves were selected, ranging from 4 to 10 months-old, free of anaplasmosis, from an establishment located in the Province of Corrientes, Argentina. The batch was divided into two groups, one received the cryopreserved vaccine and the other was not vaccinated (control group). Serum samples were taken at 0, 30 and 60 days after vaccination (dav), and immunity induced by the vaccine was evaluated by ELISA (enzyme-linked immuno sorbent assay). At 15-30-45 and 60 dav, blood samples were analyzed from 3 calves of each group for the identification and differentiation of Anaplasma sp by polymerase chain reaction (PCR). ELISA was negative for the 20 calves analyzed on the day of vaccination; at 30 dav two calves of the vaccinated group were positive while the calves of the control group were negative. At 60 dav, 80% of the calves in the vaccinated group were positive to ELISA and two animals in the control group were suspect. PCR revealed the presence of A. centrale  at 60 dav, not only in the three calves of the vaccinated group but also in three animals of the control group. The latter could be attributed to horizontal transmission by iatrogenesis or through vectors. A. marginale was not identified. The lack of detection of specific antibodies at 60 dav in two vaccinated calves, not analyzed by PCR, could correspond to a longer incubation period, and later controls should have been performed. It is concluded that the cryopreserved monovalent vaccine of A. centrale confers an adequate immunity for the prophylaxis of anaplasmosis in calves, thus being a valid alternative for those establishments of tick-free zones. Absence of A. marginale as well as horizontal transmission of the vaccine strain were confirmed.