Comparison of propagation and continuous passages of Neospora caninum tachyzoites in Vero and TLI cell lines

Neospora caninum causes major bovine abortions and neonatal mortality in cattle, sheep, goat and horse. Vero cells are the most frequently used cell line for culture of Neospora caninum but problems are with propagation and required level of nutritional components for the media persist. In this study the tachyzoite yields of N. caninum were compared in two cell lines: Vero (African Green Monkey Kidney) and suspension culture Theileria lestoquardi-infected lymphoblastoid (TLI) cell lines. Then, N. caninum were continuously passaged in these cell lines for 3 months and the effect of host cells on virulence of tachyzoites was assessed by broiler chicken embryonated eggs. Inoculation was performed in the chorioallantoic (CA) liquid of the embryonated eggs with different dilutions (0.5× 104, 1.0× 104, 1.5× 104) of tachtzoites isolated from these cell cultures. The mortality pattern and pathological changes of the dead embryos and hatched chickens were noted. Tissue samples of brain, liver and heart were examined by histopathological and detection of DNA of parasite by polymerase chain reaction (PCR). Also, consecutive sections of the tissues examined histologically were used for immunohistochemical (IHC) examination. Results of the present study did not show any significant differences in number of tachyzoites harvested from both cell line and also in mortality rate of inoculated embryonated eggs. Attenuation of virulence after 3 months continuous passages of suspension culture of TLI cell line was not different with Vero cell line which the results were confirmed by histopathology, IHC and PCR.Continuous passage of Neospora caninum in both cell lines were similar suggesting that TLI cells could be used for vaccine production.