Southeast Asian Foot-and-Mouth Disease Viruses in Eastern Asia

Foot-and-mouth disease (FMD) outbreaks recently affected 2 countries (Japan and South Korea) in eastern Asia that were free of FMD without vaccination. Analysis of viral protein 1 nucleotide sequences indicated that FMD serotype A and O viruses that caused these outbreaks originated in mainland Southeast Asia to which these viruses are endemic.

Foot-and-mouth disease (FMD) outbreaks recently affected 2 countries (Japan and South Korea) in eastern Asia that were free of FMD without vaccination. Analysis of viral protein 1 nucleotide sequences indicated that FMD serotype A and O viruses that caused these outbreaks originated in mainland Southeast Asia to which these viruses are endemic.
F oot-and-mouth disease (FMD) is a highly contagious transboundary disease that affects domesticated animals and wildlife in Africa, Asia and parts of South America. Outbreaks of FMD in these disease-endemic regions continuously threaten livestock industries in countries that are free of FMD (with or without vaccination). The causative agent, FMD virus (FMDV), is a small, nonenveloped, picornavirus (genus Aphthovirus) that has 7 serotypes. This virus is easily transmitted by movement of infected livestock or animal products, contaminated persons, objects, and aerosols.  Figure, wwwnc.cdc.gov/EID/article/18/3/11-0908-FA1.htm). In 1999-2002, extensive outbreaks caused by the PanAsia strain of serotype O were reported in Japan, South Korea, China, Taiwan, and Russia (8)(9)(10). The purpose of this study was to determine the origins of recent FMD outbreaks in eastern Asia.

The Study
FMDVs characterized by antigen ELISA as serotype A were isolated from samples collected from FMD fi eld outbreaks in Hubei Province, China, and in Gyeonggido Province, South Korea. Before FMD cases appeared in China in January 2009, serotype A infections had not occurred in that country China since 1964 (11), and until serotype A appeared in South Korea in January 2010, that country had been free of FMD without vaccination (for all FMDV serotypes) since 2002.
Phylogenetic analysis (12) showed that VP1 sequences  Similar outbreaks occurred during 2010 that were caused by an FMD lineage of serotype O that is endemic to Southeast Asia (online Appendix Figure, panel B). As of 2011, outbreaks caused by this serotype continue to occur across a wide region (online Appendix Figure,  VP1 sequences generated in the United Kingdom, China, Japan, South Korea, and Russia and those available in GenBank were analyzed by using by MEGA5 (12). Analysis showed that FMDVs causing serotype O outbreaks form 2 genetic clusters related to viruses within the Southeast Asia topotype (O/SEA/Mya-98 lineage), which are usually restricted to mainland Southeast Asia (online Appendix Figure, panel B). There was >97.3% sequence relationship between sequences for FMDVs from China and those from outbreaks in Hong Kong, South Korea, and Japan.
Sequences for viruses collected in Mongolia were distinct (differing by 11.9% nt identity) and more closely related to other viruses collected during 2009 and 2010 in Southeast Asia (Thailand, Vietnam and Malaysia) (6). The 2 outbreaks in Russia (July and August 2010), which were caused by viruses from 2 of these sublineages, were located close to the borders with China and Mongolia and separated by ≈250 km. These outbreaks represent 2 distinct introductions of FMD into Russia.

Conclusions
Sequence data implicate regions of mainland Southeast Asia to which FMD is endemic as the source of serotype O and A FMDVs that have caused recent outbreaks in eastern Asia. These events are not unprecedented; a previous instance of spread of FMDV from Southeast Asia into China (Yunnan Province) in 2006 involved the Asia 1 serotype. Furthermore, FMDV O/SEA topotype (Mya-98) was also detected in China in 2003 and in Mongolia in 2004. These fi ndings provide evidence for the porous nature of borders between mainland Southeast Asia and neighboring countries and highlight the continued threat posed by FMD as a transboundary disease in the region. The extent to which viruses have spread into countries that were previously free of FMD (without vaccination) is a cause for concern.
Although VP1 sequence data can be used to characterize the viruses that are causing these outbreaks, further coordination and sharing of sequence data are now urgently required to formally identify transboundary transmission links between affected countries in the region. Complete FMDV genome sequence analyses from these fi eld cases and additional material may provide a suitable approach to reconstruct high-resolution transmission trees and connect clusters of outbreaks (13,14).
This report describes recent incursion of FMDVs from Southeast Asia into eastern Asia. In vitro vaccine matching data (from the Institue of Animal Health) indicate that currently available vaccine strains (A/May/97and O/ Manisa) should protect against representative isolates of these 2 serotypes. However, close monitoring of antigenicity and of the spread of these lineages from Southeast Asia is essential to ensure that risks for further and continued outbreaks can be mitigated.