An emerging recombinant human enterovirus 71 responsible for the 2008 outbreak of hand foot and mouth disease in Fuyang city of China

Abstract

Hand, foot and mouth disease (HFMD), a common contagious disease that usually affects children, is normally mild but can have life-threatening manifestations. It can be caused by enteroviruses, particularly Coxsackieviruses and human enterovirus 71 (HEV71) with highly variable clinical manifestations. In the spring of 2008, a large, unprecedented HFMD outbreak in Fuyang city of Anhui province in the central part of southeastern China resulted in a high aggregation of fatal cases. In this study, epidemiologic and clinical investigations, laboratory testing, and genetic analyses were performed to identify the causal pathogen of the outbreak. Of the 6,049 cases reported between 1 March and 9 May of 2008, 3023 (50%) were hospitalized, 353 (5.8%) were severe and 22 (0.36%) were fatal. HEV71 was confirmed as the etiological pathogen of the outbreak. Phylogenetic analyses of entire VP1 capsid protein sequence of 45 Fuyang HEV71 isolates showed that they belong to C4a cluster of the C4 subgenotype. In addition, genetic recombinations were found in the 3D region (RNA-dependent RNA polymerase, a major component of the viral replication complex of the genome) between the Fuyang HEV71 strain and Coxsackievirus A16 (CV-A16), resulting in a recombination virus. In conclusion, an emerging recombinant HEV71 was responsible for the HFMD outbreak in Fuyang City of China, 2008.

Figure 1

Distribution of hand, foot, and mouth disease (HFMD) patients in Fuyang City, Anhui province, by date. By 31 May 2008, the outbreak had affected 6883 children (This study focused on the outbreak between March 1 and May 9 of 2008, which included 6049 reported cases). The bold slipped arrows indicated the death dates of initial 5 fatal cases.

Figure 2

Phylogenetic dendrogram were drawn on the basis of the 891-nt sequence of entire VP1 gene using the Neighbor-Joining method of MEGA software (version 4.0) for 14 selected Fuyang representative isolates and other HEV71 strains of known subgenotypes listed in Table 1. The bootstrap values from 1000 pseudoreplicates for major lineages within the tree are shown as percentages. The prototype CVA16 strain (G-10) was used as outgroup. Solid diamond indicated the fatal cases; Solid triangle indicated the severe cases; Solid round indicated the outpatients; Triangle indicated the HEV71 sequences from other provinces in China between 1997-2008 available in GenBank database.

Figure 3

A: Phylogenetic analysis based on the entire 3D gene. The trees were drawn on the basis of the 1368-nt sequence including the noncoding region using the Neighbor-Joining method of MEGA software (version 4.0). Solid diamond indicated the fatal cases; Solid triangle indicated the severe cases; Solid round indicated the mild cases; Triangle indicated the HEV71 sequences from other provinces in China between 1997 and 2008(available from GenBank). The scale bar indicates the number of nucleotide substitutions per site. B: similarity plot and bootscan identified the recombinant sequences in 3D region of genome of HEV71. The window size of 200-nt slides in increments of 20 nt at a time. The Kimura model with the Jukes-Cantor correction was used. The vertical axis indicates the percent nucleotide identities between strain Fuyang 2008, CV-A16, and HEV71 strain. The horizontal axis indicates the nucleotide positions of the entire genome.