| In 2010-2011, foot-and-mouth disease(FMD) outbreaks caused by O/SEA/Mya-98 lineage have affected Eastern Asia and these outbreaks caused serious economic consequences to affected countries. During this endemic, 337 FMD outbreaks have been reported only in China, Japan, South Korea, Mongolia and Russia. Among these outbreaks, strains with distinctive S-fragment were isolated in two outbreaks and the representative strains were O/HKN/20/2010 isolated in Hong Kong and O/GSLX/CHN/2010 isolated in Linxia, Gansu Province, China. Compared with other Mya-98 lineage epidemic isolates, these two isolates have obvious characteristics: an unexpected 70-nucleotide(nt) deletion in the middle of the S-fragment and several base mutations in the latter half of the S-fragment. The distinctive S-fragment has been noticed by a number of scientists.In this work, a reverse genetics approach was used to identify the influence of the distinctive S-fragment on virus replication and virulence in suckling mice. First, the infectious c DNA clone of foot-and-mouth disease virus(FMDV) strain O/GSLX/CHN/2010 has been constructed and the genetically engineered virus r GS has been rescued. Second, based on two existing full-length infectious c DNA clones with the same lineage to O/GSLX/CHN/2010, two chimeric foot-and-mouth disease viruses bearing the S-fragment of O/GSLX/CHN/2010 were constructed and rescued using reverse genetics manipulation. Then, the viral replication and virulence in suckling mice of these two chimeric viruses have been evaluated.The results showed that the viral replication of O/GSLX/CHN/2010 as well as r GS were slow and the virulence in suckling mice of this strain was low, while the viral replication of chimeric viruses were not as slow as O/GSLX/CHN/2010 and the virulence in suckling mice of chimeric viruses were not as low as O/GSLX/CHN/2010 either. The results indicated that the whole S-fragment of O/GSLX/CHN/2010 could not determine the weak phenotype of O/GSLX/CHN/2010 alone and mutations along the genome of O/GSLX/CHN/2010 might contribute to the weak phenotype. Among these mutations, the influence of the unusual insertion of an amino acid into the L protease on virus biological characteristics is worthy of attention. And we speculate that the deletion in the middle of the S-fragment is cleaved at one time by a kind of ribonuclease. These studies lay the foundation for futher researches of the S-fragment function and the mechanism behind the low-level replication of FMDV O/GSLX/CHN/2010. |
