Molecular evolution of two asymptomatic echovirus 6 strains that constitute a novel branch of recently epidemic echovirus 6 in China

Abstract

BackgroundEchovirus 6 (E6) infections are associated with aseptic meningitis and acute flaccid paralysis (AFP). But some infections, sometimes most of them, are asymptomatic. The mechanism of E6 virulence is unknown. Analyses of the molecular evolution of asymptomatic E6 may help understand why the infections show different manifestations.MethodsNinety-six stool samples of healthy children in Yunnan, China were collected and two E6 strains were isolated from them. The whole genomes of these two E6 strains were sequenced, and their molecular evolution was analyzed.ResultsThe results showed that the two E6 strains may be derived from KJ7724XX strains, which were predominant in AFP patients in Shangdong in 2011. The evolution was accelerated when the two E6 strains formed, although no positive selection site was found. The 11 exclusive mutations on which selection force significantly changed were found in the 2C, 3AB and 3C genes.ConclusionThere are some E6 strains which did not cause the disease in the children of Yunnan. These E6 strains maybe come from a recombinant E6 strain which was associated with the outbreak of AFP in Shangdong in 2011. However, some new mutations were found in the 2C, 3AB and 3C genes of these asymptomatic strains, and these mutations may be constraint by the natural selection and could be potentially responsible for clinical presentations.Electronic supplementary materialThe online version of this article (doi:10.1186/s12985-017-0809-2) contains supplementary material, which is available to authorized users.

Aseptic meningitis outbreak associated with echovirus 4 in Northern Europe in 2013–2014

“…Long-term surveillance data suggests that E4 outbreaks are followed by irregular intervals of low activity [30]. In addition to E4, meningitis cases caused by other echoviruses have been reported regularly in Europe and Asia [31][32][33][34][35][36].…”

Molecular characterization of echovirus 12 strains isolated from healthy children in China

“…The children were asymptomatic and did not present a fever, cough, or rash and did not have contact with patients recently infected by EVs in the 2 weeks before sample collection. The children’s ages ranged from 3 to 6 years 31 . The cell line, KMB17, was used to isolate viruses from the stool specimens according to the standard procedures 32 .…”

Molecular epidemiological characteristics of echovirus 6 in mainland China: extensive circulation of genotype F from 2007 to 2018

“…Echovirus 6 (E6), a member of the species Enterovirus B, is a common virus that causes a wide range of diseases in humans. Although infection in immunocompetent individuals is often asymptomatic or induces mild fever, E6 is a common etiological agent in nervous system diseases, including aseptic meningitis (AM), encephalitis, and acute flaccid paralysis (AFP) [2][3][4][5], and it can cause persistent and/or widely disseminated systemic infection in immunosuppressed individuals and neonates [6][7][8][9].…”