Bovine babesiosis live vaccine production: use of gamma irradiation on the substrate.

Gamma irradiation on bovine serum and red blood cells (RBC) allows proliferation and growth of in vitro-cultured Babesia sp., and has potential application to inactivate contaminating viruses and bacteria from the substrate. Gamma irradiation with 25 kGy in a source of (60)Co was able to inactivate infectious bovine rinotracheitis (IBR) and bovine viral diarrhea (BVD) viruses in artificially contaminated serum; besides, bacteria were also eliminated. In vitro culture of Babesia bovis (B. bovis) in modified substrate, by adding irradiated serum with (60)Co at 25 kGy was propagated from 24-well culture plates to 225 cm(2) tissue culture flasks, and percentages of parasitized erythrocytes (PPE) from 2.4% to 8.8% were obtained. Infected RBC adapted to Irrad S were transferred to the irradiated substrate in vitro culture system, by using serum irradiated at 25 kGy and RBC from 10 to 70 Gy. The PPE ranged from 3.1 to 11. Culture of Babesia bigemina (B. bigemina) was established with Irrad S (25 kGy); its propagation was achieved in tissue culture flasks reaching PPE from 0.5 to 4.3 with no statistical difference (P > 0.05) when compared to the nonirradiated control culture (1.2-4.8). B. bigemina-infected RBCs were transferred to the modified culture system by adding irradiated serum and RBC (25 kGy and 70 Gy, respectively). PPE obtained in culture flasks were from 0.8 to 4.2. The results indicate that gamma irradiation is a suitable method to inactivate potential viral contamination and eliminate bacteria from bovine serum, to produce a live attenuated vaccine through the in vitro culture.