Reemergence of enterovirus 71 in 2008 in taiwan: dynamics of genetic and antigenic evolution from 1998 to 2008

Abstract

In recent years, enterovirus 71 (EV71) has been a cause of numerous outbreaks of hand-foot-and-mouth disease, with severe neurological complications in the Asia-Pacific region. The reemergence in Taiwan of EV71 genotype B5 in 2008 resulted in the largest outbreak of EV71 in Taiwan in the past 11 years. Phylogenetic analyses indicated that dominant genotype changes from B to C or C to B occurred at least three times between 1986 and 2008. Furthermore, antigenic cartography of EV71 by using neutralization tests revealed that the reemerging EV71 genotype B5 strains formed a separate cluster which was antigenically distinct from the B4 and C genotypes. Moreover, analyses of full-length genomic sequences of EV71 circulating in Taiwan during this period showed the occurrence of intra- and interserotypic recombination. Therefore, continuous surveillance of EV71 including the monitoring of genetic evolution and antigenic changes is recommended and may contribute to the development of a vaccine for EV71.

FIG. 1.

Phylogenetic analysis of the VP1 protein coding region of EV71. Phylogenetic analysis of the VP1 protein coding regions of EV71 isolates from 1986 and from 1998 to 2008 from Taiwan and from reference strains from the GenBank based on the VP1 protein coding region (nucleotides 2439 to 3278; 840 bp). The phylogenetic tree was estimated under the general time reversible model with the program PAUP*, version 4.0b. Bootstrap values (percentage of 1,000 pseudoreplicate data sets) of over 75% supporting each cluster are shown at the nodes. CA16 was included as an outgroup. AUS, Australia; SAR, Sarawak, Malaysia; KOR, Korea; SIN, Singapore.

FIG. 2.

Antigenic map of EV71 isolates from 1998 to 2008 isolated in Taiwan. The relative positions of strains (colored shapes) and antisera (uncolored shapes) were adjusted such that the distances between strains and antisera in the map represent the corresponding neutralization assay measurements (see Table S2 in the supplemental material) with the least error. The periphery of each shape denotes a 0.5-unit increase in the total error; thus, size and shape represent a confidence area in the placement of the strain or antiserum. The vertical and horizontal lines represent antigenic distance, and because only the relative positions of antigens and antisera can be determined, the orientation of the map within these axes is free. The spacing between grid lines is 1 unit of antigenic distance, corresponding to a twofold dilution of antiserum in the neutralization assay. Isolate number and genotype of viruses or serum numbers and genotype of infected viruses are indicated.

FIG. 3.

Dynamic analysis of EV71 genetic recombination from 1998 to 2008. Complete genome sequences of EV71 isolates of various genotypes were analyzed by bootscan analysis, including 1998 viruses (A), N7008-TW99 (B), N2838-TW03 (C), and S0584-TW04 (D). This analysis was calculated by SimPlot, version 3.5.1, using the neighbor-joining tree algorithm (Kimura distance model) in a sliding window of 500 bp with a 20-bp step. The EV71 genetic map is shown at the top of each panel.

FIG. 3.

Dynamic analysis of EV71 genetic recombination from 1998 to 2008. Complete genome sequences of EV71 isolates of various genotypes were analyzed by bootscan analysis, including 1998 viruses (A), N7008-TW99 (B), N2838-TW03 (C), and S0584-TW04 (D). This analysis was calculated by SimPlot, version 3.5.1, using the neighbor-joining tree algorithm (Kimura distance model) in a sliding window of 500 bp with a 20-bp step. The EV71 genetic map is shown at the top of each panel.