Surveillance and genetic characteristics of echovirus 6 strains isolated from environmental sewage and aseptic encephalitis cases

Abstract

Objective To analyze the genetic characteristics of echovirus 6 (E-6) strains isolated from patients with acute meningitis/encephalitis syndrome (AMES) in 2014 and sewage samples in 2013—2014 in Shandong province and to investigate their correlations. Methods Enterovirus strains were isolated from cerebrospinal fluid, stool and throat swab samples collected from 940 cases of AMES and 96 sewage samples used for environmental surveillance. The positive isolates were identified by molecular typing method. Homologous and phylogenetic analyses based on the VP1 sequences of E-6 isolates were performed. Results Altogether 47 E-6 strains were isolated from patients with AMES in 2014, accounting for 29.56% of all isolated enteroviruses (EVs) strains. No E-6 strains were isolated from AMES cases in 2013. Data of the environmental surveillance showed that E-6 virus strains had been frequently detected in sewage samples since the summer of 2013 to the end of 2014. In total, 40 E-6 virus strains were isolated (7.87% of total isolated EVs strains) in 2013 and 139 E-6 virus strains (26.18%) in 2014. Phylogenetic analysis indicated that the E-6 isolates recruited in this study belonged to clusters A and C with high intracluster sequence identities between AMES and environmental isolates. The nucleotide identities were 98.3%-100% among cluster A E-6 virus strains isolated from AMES cases in 2014 and 96.6%-100% among cluster A E-6 virus environmental isolates during the surveillance year 2013—2014. The cluster A E-6 virus strains shared 97.1%-100% nucleotide identities between the AMES and environmental isolates. For cluster C E-6 virus strains, the nucleotide identities were 100%, 98.7%-100% and 99.1%-100%, respectively. Conclusion The epidemic of viral encephalitis in Shandong province in 2014 was associated the transmission of two lineages of E-6 virus. Environmental surveillance revealed the potential epidemic of E-6 virus even before the epidemic of viral encephalitis in Shandong province, indicating the possibility of using environmental surveillance for early warning of related diseases. Key words: Viral meningitis; Viral encephalitis; Environmental surveillance; Human echovirus 6; Sequence homology; Phylogeny