Foot-and-mouth disease (FMD) is endemic across Asia and three serotypes are in circulation, namely O, A and Asia1. Viruses belonging to O and A serotypes have caused major outbreaks in the South East Asian region, in both endemic and previously disease free countries. Different vaccine strains are used throughout the region and concern exists that some do not match the currently circulating field strains.
This study reports the vaccine matching and genetic characterisation of serotype A and O isolates circulating in SEA, predominantly Thailand, with a view to compare and recommend suitable vaccine strains for use in the region, as well as the vaccine bank of Australia. Antigen matching studies were performed with three vaccine strains each of serotype A and serotype O against viruses collected from South-East Asian countries including Thailand, Vietnam, Laos PDR and Cambodia, and relative homology (r1) values against each of the vaccine strains determined. In addition, phylogenetic trees were drawn using VP1 sequence data. These trees, based on the results from the OIE Reference Laboratory for FMD in SEA, Pakchong, showed the emergence of three variant clusters during 2004–2008, 2010–2013 and 2014–present, for serotype A isolates. Viruses from these clusters showed differential homology to the commercial vaccine strains often present in vaccine banks, but most had satisfactory antigenic relationships with the Thailand vaccine strains.
Continued monitoring for the emergence of variant strains in SEA is required for effective control of the disease in this region. Collection and shipping of samples from remote areas in the region remain challenging and need to be addressed to ensure potential emerging viruses are further characterised in specialised laboratories. Australia is committed to working closely with the countries in the region for management and control of the disease.