Molecular Epidemiology and Evolution of Human Enterovirus Serotype 68 in Thailand, 2006–2011

Abstract

BackgroundPublications worldwide have reported on the re-occurrence of human enterovirus 68 (EV68), a rarely detected pathogen usually causing respiratory illness. However, epidemiological data regarding this virus in particular on the Asian continent has so far been limited.Methodology/FindingsWe investigated the epidemiology and genetic variability of EV68 infection among Thai children with respiratory illnesses from 2006–2011 (n = 1810). Semi-nested PCR using primer sets for amplification of the 5′-untranslated region through VP2 was performed for rhino-enterovirus detection. Altogether, 25 cases were confirmed as EV68 infection indicating a prevalence of 1.4% in the entire study population. Interestingly, the majority of samples were children aged >5 years (64%). Also, co-infection with other viruses was found in 28%, while pandemic H1N1 influenza/2009 virus was the most common co-infection. Of EV68-positive patients, 36% required hospitalizations with the common clinical presentations of fever, cough, dyspnea, and wheezing. The present study has shown that EV68 was extremely rare until 2009 (0.9%). An increasing annual prevalence was found in 2010 (1.6%) with the highest detection frequency in 2011 (4.3%). Based on analysis of the VP1 gene, the evolutionary rate of EV68 was estimated at 4.93×10−3 substitutions/site/year. Major bifurcation of the currently circulating EV68 strains occurred 66 years ago (1945.31 with (1925.95–1960.46)95% HPD). Among the current lineages, 3 clusters of EV68 were categorized based on the different molecular signatures in the BC and DE loops of VP1 combined with high posterior probability values. Each cluster has branched off from their common ancestor at least 36 years ago (1975.78 with (1946.13–1984.97)95% HPD).ConclusionDifferences in epidemiological characteristic and seasonal profile of EV68 have been found in this study. Results from Bayesian phylogenetic investigations also revealed that EV68 should be recognized as a genetically diverse virus with a substitution rate identical to that of enterovirus 71 genotype B (4.2×10−3 s/s/y).

Antigenic and Receptor Binding Properties of Enterovirus 68

“…According to our previous reports, most of the EV68 strains detected in the Philippines belonged to lineage 2, and a few of them belonged to lineage 3 (4,10). The VP1 sequences detected in the Philippines and other countries demonstrated that the amino acid sequence patterns in BC and DE loops were correlated with the categorization of EV68 into the 3 lineages (6,8,10). Generally, loop structures, including BC and DE loops, are located on the viral surface and associated with antigenic epitopes of enteroviruses (11,12).…”

“…This suggests that although each of the antisera generated for three lineages was cross-reactive to the strains of other lineages, there were some antigenic differences between lineages 1, 2, and 3 of EV68, although they belong to the single homologous serotype. Several previous studies have shown that multiple lineages of EV68 were detected in each outbreak (6,8,10). The emergence and cocirculation of strains with various antigenic properties in the same community may be a possible mechanism for the rapid increase of EV68 cases in recent years.…”

“…In one previous study from Finland, it was reported that the mean NT titers of serum from pregnant women against strain Fermon were lower in samples which were collected more recently (26). In addition, some of the previous studies using the Markov chain Monte Carlo approach suggested that EV68 went through extensive genetic evolution in the 1990s and 2000s, which may have resulted in the emergence of three lineages (6,8). It may be possible that those genetic evolutions resulted in the emergence of strains with antigenic differences from previously circulating strains in recent years.…”

“…In an enterovirus surveillance conducted in the United States from 1970 to 2005, only a total of 26 strains were reported over 35 years (2). However, the number of reported EV68 cases increased dramatically in the late 2000s, in different parts of the world (3)(4)(5)(6)(7)(8). The underlying molecular mechanism for this sudden increase of EV68 detections in recent years is still unknown.…”

“…Moreover, it was previously demonstrated that amino acid changes in the BC loop of coxsackievirus B4 resulted in loss of virus neutralization by serotype specific antisera, suggesting that the BC loop has an important role in determining antigenicity of the virus (13). Therefore, it was speculated that amino acid changes in the BC and DE loops of EV68 might also be associated with altered antigenicity of EV68 strains detected in recent years (6,8).…”