Molecular Evolution of Enterovirus 68 Detected in the Philippines

Background
Detection of Enterovirus 68 (EV68) has recently been increased. However, underlying evolutionary mechanism of this increasing trend is not fully understood.
Methods
Nasopharyngeal swabs were collected from 5,240 patients with acute respiratory infections in the Philippines from June 2009 to December 2011. EV68 was detected by polymerase chain reaction (PCR) targeting for 5′ untranslated region (5′UTR), viral protein 1 (VP1), and VP4/VP2. Phylogenetic trees were generated using the obtained sequences.
Results
Of the 5,240 tested samples, 12 EV68 positive cases were detected between August and December in 2011 (detection rate, 0.23%). The detection rate was higher among inpatients than outpatients (p<0.0001). Among VP1 sequences detected from 7 patients in 2011, 5 in lineage 2 were diverged from those detected in the Philippines in 2008, however, 2 in lineage 3 were not diverged from strains detected in the Philippines in 2008 but closely associated with strains detected in the United States. Combined with our previous report, EV68 occurrences were observed twice in the Philippines within the last four years.
Conclusions
EV68 detections might be occurring in cyclic patterns, and viruses might have been maintained in the community while some strains might have been newly introduced.

研究背景
近期肠道病毒68型（Enterovirus 68, EV68）的检出率呈上升趋势，但该趋势背后的潜在进化机制尚未完全阐明。

研究方法
2009年6月至2011年12月间，从菲律宾5240例急性呼吸道感染患者中采集鼻咽拭子样本。采用针对5′非翻译区（5′ untranslated region, 5′UTR）、病毒蛋白1（viral protein 1, VP1）及VP4/VP2的聚合酶链反应（polymerase chain reaction, PCR）对EV68进行检测，基于获取的序列构建系统发育树。

研究结果
在所检测的5240份样本中，2011年8月至12月间共检出12例EV68阳性病例，检出率为0.23%。住院患者的EV68检出率高于门诊患者（p<0.0001）。2011年从7例患者体内检出的VP1序列中，5株属于谱系2，与2008年菲律宾地区检出的毒株存在遗传分化；另有2株属于谱系3，与2008年菲律宾检出的毒株无遗传分化，但与美国检出的毒株亲缘关系密切。结合本团队此前的研究报告，近四年内菲律宾地区已两次出现EV68感染事件。

研究结论
EV68的检出可能呈现周期性循环模式，病毒或可在社区中持续维持传播，同时亦有部分毒株为新近引入的外来毒株。