Phylogenetic Characterization and Pathogenicity in Cattle and Pigs of Foot‐and‐Mouth Disease Viruses Circulating in Myanmar Between 2016 and 2022

Foot-and-mouth disease (FMD) is a highly contagious and serious transboundary disease affecting cloven-hoofed animals. Myanmar is a critical area for FMD outbreaks in Southeast and East Asian regions because of its geographical location bordering South Asian countries and its cattle industry. Phylogenetic characterization and pathogenicity in susceptible animals of circulating viruses in Myanmar are essential to prepare the rapid and accurate diagnosis and implement effective FMD prevention. This study analyzed a total of 34 vesicular epithelial samples collected from FMD cases in northern, central, and southern Myanmar between 2016 and 2022. Phylogenetic analysis of VP1 nucleotide sequences revealed multiple serotypes and topotypes between 2016 and 2019, including serotype O/Middle East-South Asia (ME-SA) topotype (O/ME-SA/Ind-2001e) and Southeast Asia (SEA) topotype, and serotype A/ASIA topotype. Subsequently, all viruses across Myanmar detected from 2019 to 2022 belonged to O/ME-SA/Ind-2001e. Phylogenetic analysis of the whole genome sequence showed that O/ME-SA/Ind-2001e viruses detected after 2019 were classified into a different genetic group with those of 2016 isolates in Myanmar. Based on phylogenetic analysis, one representative strain from 2019 that was genetically similar to viruses detected from 2019 to 2022 and to a 2022 Indonesian isolate was selected for pathogenicity testing in comparison with a 2016 strain closely related to viruses from neighboring countries. Both strains were used for experimental infection in pigs and showed similar pathogenicity. The 2019 strain was additionally tested in cattle and caused typical FMD pathogenicity, including vesicular development and virus excretion. Viral genes and antibodies in infected animals were detectable using existing diagnostic methods, which are considered useful for identifying currently circulating viruses. These results elucidate the subtypes of FMD viruses (FMDVs) circulating in Myanmar, their phylogenetic relationships with viruses from neighboring Asian countries, their pathogenicity, and the applicability of available diagnostic methods. It offers insights into appropriate control strategies against FMD in Southeast and East Asian regions.