Babesia organisms are hemoprotozoa isolated from people and animals. Their in vitro cultivation supplies information about the morphology and ultrastructure of these parasites. They make it possible to obtain the genetic material for diagnostic elaborations and for detections of phylogenetic relationships between various species of Babesia. Protozoa cultivated on red blood cells can be a source of parasite antigen or attenuated strains of protozoa which can be used for vaccinations. The cultures of Babesia species are kept in an erythrocytes host, taken from the animals from which Babesia is most frequently isolated, suspended in tissue culture media with the addition of sera, in microaerophil conditions at 37°C. The specific circumstances and factors that are needed to obtain an effective Babesia culture are very often the reason of the failure of these investigations.
It was found that M-PI3 virus could be propagated both in MDBK and FLK cells. TCID₅₀ in the MDBK cell line was 10⁶‧³⁵—10⁷‧⁵ per 0.2 ml in the course of 10 consecutive passages and haemagglutination titer ranged from 80 to 320 using a 0.75 per cent solution of goose erythrocytes. There was observed many mitotic divisions of cells revealed by Pappenheim’s staining. The M-PI3 virus passaged through FLK cells displayed changed biological properties compared with that propagated in MDBK cells. TCID₅₀ and haemagglutination titers of M-PI3 virus depended on the number of passages and infective dose. In the first four passages its TCID₅₀ titer was 10⁵‧³³—10⁶‧⁶⁰ per 0.2 ml, in the 5th — 10³‧³² and in the 6th — 10¹‧⁵. The virus was not found in the next four passages. Similar observations were done with respect to haemagglutination titer; in the first passage its titer was 320, in the 4th — 20 and later no virus was stated. By means of Pappenheim’s method the FLK cells formed syncytia containing 20—40 nuclei. The mean geometric titer of antibodies in sera taken from calves infected with BLV and M-PI3 viruses were 507 and in the group II i.e. infected only with M-PI3 virus — 226. The highest titer of HI antibodies in the group I was found at week 3 p.i. and in the group II at week 4 p.i.