Construction of Full-length Infectious Clone for Encephalomyocarditis Virus BJC3 and Identification of the Rescued Virus

The objective of this study was to construct the infectious clone of encephalomyocarditis virus (EMCV) BJC3 strain.The genomic cDNA of the virus was amplified by three overlapping segments using RT-PCR,and cloned into low-copy plasmid pWSK29 to construct the full-length cDNA clone pWSKBJC3/ w.The pWSKBJC3/w was in vitro transcribed and transfected into BHK-21 cells to rescue the virus.The results showed that the full-length cDNA clone was infectious and the virus could be rescued in BHK-21 cells.The rescued virus designated RvBJC3W was identified by RT-PCR and indirect immunofluorescence assay(IFA).The rescued virus had similar growth characteristics to its parental virus BJC3 and retained pathogenicity for mice.Our results indicate that the first infectious cDNA clone of EMCV in China has been successfully established and provides an essential tool for investigating the molecular basis of pathogenicity of EMCV.

Isolation, Molecular and Phylogenetic Analysis of Porcine Encephalomyocarditis Virus Strain HLJ in China

Encephalomyocarditis virus(EMCV)is a positive single-stranded small RNA virus without envelope,which can infect a variety of mammals.Swines are the most susceptible animals,which can cause acute myocarditis and respiratory failure in piglets and reproductive failure in pregnant sows.Diseases caused by EMCV have a wide range of effects on the global swine industry.In this study,a strain of EMCV was isolated from a swine aborted fetus in northeast China.It was identified by reverse transcriptase polymerase chain reaction(RT-PCR),electron microscopic observation and indirect immunofluorescence assay.The subsequent results showed that the virus titer of HLJ strain grew to 8.3 lgTCID50 on baby hamster kidney 21(BHK-21)cells.And HLJ strain caused the specific cytopathic effect(CPE)on BHK-21 cells and severe pathological changes in mice.Complete genome sequencing and multiple sequence alignment showed that the homology between HLJ strain and other isolates worldwide was 71.5%-99.7%.Phylogenetic analysis showed that EMCV isolates fell into five clusters:lineageⅠ,Ⅱ,Ⅲ,ⅣandⅤ,based on the nucleotide sequences of the entire open reading frame(ORF)and VP1 gene.HLJ isolate was grouped into lineage I.The analyses of amino acid mutation sites of VP1 protein showed that the amino acids at positions 20 and 54 in VP1 junction were unique to HLJ strain.The isolation of HLJ strain enriched the epidemiological database of EMCV.

Alteration of encephalomyocarditis virus pathogenicity due to a mutation at position 100 of VP1

Encephalomyocarditis virus (EMCV) infection leads to many diseases including encephalitis,myocarditis and diabetes in its natural host,the mouse.In this study,we generated four cDNA clones with a point mutation at position 100 of VP1.The amino acids isoleucine,alanine,serine and proline were substituted with threonine in the four different clones of EMCV strain BJC3 by site-specific mutagenesis,and viable viruses were rescued.Although all mutants and wild-type viruses display different plaque morphologies,they replicate comparably in BHK-21 cells.The pathogenicity of the mutated viruses was systematically analyzed to investigate the importance of this amino acid in the viral pathogenicity and disease phenotype of EMCV infection in mice.The results showed that the isoleucine(T1100I) and proline-mutated viruses (T1100P) exhibited a reduced mortality,lower cerebral virus loads and alleviated brain damage while the viruses with serine (T1100S) and alanine (T1100A) substitutions displayed similar properties as the wild-type virus.These findings indicate that the amino acid at position 100 of VP1 is important for EMCV in vivo infection,and its mutation alters the pathogenicity of viral infection in mice.