Foot-and-Mouth Disease Virus Serotype O Exhibits Phenomenal Genetic Lineage Diversity in India during 2018–2022

In India, widespread foot-and-mouth disease (FMD) outbreaks occurred in 2021. The objective of this study was to identify genetic lineages and evaluate the antigenic relationships of FMD virus (FMDV) isolates gathered from outbreaks reported between 2019 and 2022. Our study shows that the lineages O/ME–SA/Ind2001e and the O/ME–SA/Cluster-2018 were both responsible for the FMD outbreaks on an epidemic scale during 2021. This observation is in contrast to earlier findings that suggested epidemic-scale FMD outbreaks in India are often connected to a single genetic lineage. Additionally, we report here the identification of the O/ME–SA/PanAsia-2/ANT10 sub-lineage in India for the first time, which was connected to two intermittent outbreaks in Jammu and Kashmir. The current study demonstrates that the O/ME–SA/ind2001e lineage has a strong presence outside of the Indian subcontinent. Furthermore, the O/ME–SA/Cluster-2018 was observed to have a wider geographic distribution than previously, and like the O/ME–SA/Ind2001d and O/ME–SA/Ind2001e lineages in the past, it may eventually spread outside of its geographic niche. For O/ME–SA/Ind2001e and O/ME–SA/Cluster-2018, the predicted substitution rate for the VP1 region was 6.737 × 10−3 and 8.257 × 10−3 nt substitutions per site per year, respectively. The time of the most recent common ancestor of the O/ME–SA/Ind2001e and O/ME–SA/Cluster-2018 strains suggests that the viruses possibly emerged during 2003–2011 and 2009–2017, respectively. Recent sightings of the O/ME–SA/PanAsia2/ANT10 virus in India and the O/ME–SA/Ind2001e virus in Pakistan point to possible cross-border transit of the viruses. The results of a two-dimensional viral neutralization test revealed that all of the field isolates were antigenically matched to the currently used Indian vaccine strain O INDR2/1975. These results suggest that the serotype O vaccine strain can protect against outbreaks brought on by all three circulating lineages.