An Epidemiological Analysis of Enterovirus 71: Taiwan, 1998-2004
2005 Vol.21 NO.5
Enterovirus 71 (EV71) is one of the major causes of hand, foot, and mouth disease (HFMD). Sometimes a patient infected with EV71 may suffer from serious neurological manifestations including encephalitis and poliomyelitis-like paralysis. Recently isolation of EV71 and small-scale epidemics of disease caused by EV 71 have been continuing to be reported in the Western Pacific Region (WPR). Taiwan had a major outbreak of this virus in the summer of 1998, when a total of 405 suspected cases of EV71 infection with acute complications were reported. Young children and newborns compose the high-risk group of the infection and often the hardest hit victims of such outbreaks. In this study, we took clinical specimens from our stock that had been collected, isolated and identified by the Taiwan CDC and its contract laboratories as EV71 positive, analyzed them by a Reverse Transcription Polymerase Chain Reaction (RT-PCR), followed by a genomic sequencing process by amplifying the VP1 segments of the virus genome, and conducted a phylogenetic tree analysis. Our results concur with the theory that the same B and C subgenotypes of EV71 have been co-circulating throughout Australia, Malaysia, Singapore, Japan, and Taiwan over the past decade. We also found that the major subgenotype causing the 1998 Taiwan epidemic was C2, while the following five years between 1999 and 2003, the prevailing infections were caused by B4 subgenotype instead. It appears that the trend changed to yet another subgenotype C4 in 2004, which proved to be quite similar to the EV71 strain SHZH03-China which was circulating on Mainland China in the previous year. There is a sequential homologous similarity of 97~99% among the various C4 isolates collected in Taiwan, and their average homologous similarity to SHZH03-China is 96.9%.