Molecular detection and isolation of foot-and-mouth disease virus from gayal and crossbreed cattle in two recent outbreaks in Bangladesh

Foot-and-mouth disease (FMD) is a significant threat to the livestock industry, causing severe economic losses, especially in enzootic countries like Bangladesh. Despite regular immunization, managing FMD remains challenging due to the continuous mutation and generation of new genotypes of the FMD virus (FMDV). Two recent outbreaks of FMDV have occurred in several districts of Bangladesh, including Gazipur, Pabna, and Noakhali, even though cattle farms in these districts were regularly immunized with commercially available FMDV vaccines. This suggests the emergence of new FMDV strains. Thus, we aimed to molecularly identify and isolate the circulating FMDVs in these three districts, for which we collected 35 tongue epithelium samples from FMD-suspected gayal ( Bos frontalis ) and crossbreed cattle. Among the 35 samples, 80.00% (28/35) were positive by uRT-PCR. Further serotyping of the positive samples (28) using gsRT-PCR revealed three serotypes: O (35.71%), the most predominant one, A (32.14%), and Asia-1 (10.71%). Mixed infections of A + O (14.28%) and A + Asia-1 (7.15%) were also detected. Mixed infections of A + O (14.28%) and A + Asia-1 (7.15%) were also detected. Serotypes A, Asia-1, and O + A contributed equally (each 27.27%) to disease occurrence in the Gazipur district. On the other hand, the leading causes for disease were serotype O (66.67%) and A (62.50%) in Pabna and Noakhali districts, respectively.We then isolated FMDV by inoculating RT-PCR-positive samples into BHK-21 cells, and we observed successful virus propagation in 71.42% (20/28) of the positive samples. Our data indicate that, despite regular immunization, several FMDV serotypes are circulating in Bangladesh, suggesting that continuous monitoring of circulating FMD strains is crucial in implementing a strategic FMD control program.