Comparison of two continuous cell lines BHK-21 and IB-IS2 for isolating field serotypes O and A of Foot-and-Mouth disease virus.

Foot-and-mouth disease (FMD) is a highly infectious viral infection that has a significant economic impact on livestock farming worldwide. The adaptability of a field isolate of FMDV virus for rapid isolation and production of a high antigen titer is one of the concerns of vaccine preparation, which can delay and endanger effective control programs. During a period between 2019 and 2020, a total of 63 oral epithelial samples were collected from vaccinated cattle. These samples were first analyzed and typed to identify the virus using ELISA method. Subsequently, the field virus was isolated using two continuous cell lines, BHK-21 and IB-IS2. Cytopathic effects (CPE) were observed under an inverted microscope, and then viral titration of isolated viruses was determined. Of 63 samples received from 2019 to 2020, 50 samples (79.36%) were reported positive by type-specific ELISA and typed as follows: 32 samples (64%) were type O, and 18 samples (36%) were type A. Of 50 positive samples, 38 samples (76%) were isolated in the IB-IS2 cell culture (26 samples type O, 12 samples type A) and 12 samples (34%) were isolated in the BHK-21 cell culture (9 samples type O, 3 samples type A) during three consecutive passages. The mean virus titration of isolated viruses was 10 TCID in the IB-IS2 cell line and 10 TCID in BHK-21 cell line. 26 samples that were initially isolated on the IB-IS2 cell line but not on the BHK-21 cell line were successfully isolated on the BHK-21 cell line after three consecutive passages of culture on the IB-IS2 cell line. In these samples, an average increase of about 10 in TCID50 was observed. Although both studied cell lines are suitable for the culture of Foot-and-mouth Disease virus, the IB-IS2 cell line is particularly suitable for the isolation of field viruses. While according to the virus titer (TCID50) produced in the BHK-21 cell line, this cell line is suitable for large-scale virus culture and appropriate for the production of inactivated vaccines.