Genetic diversity of coxsackievirus A16 associated with hand, foot, and mouth disease epidemics in Japan from 1983 to 2003

Abstract

To clarify the chronologic genetic diversity of coxsackievirus A16 (CV-A16) strains associated with hand, foot, and mouth disease (HFMD) epidemics in a restricted area and their genetic relation with those isolated in other areas, we investigated the genetic diversity of the 129 CV-A16 strains associated with HFMD epidemics in Fukushima, Japan, from 1983 to 2003, and compared their genetic relation to 49 CV-A16 strains isolated in other areas of Japan and in China by using phylogenetic analysis based on the VP4 sequences. Phylogenetic reconstruction of the CV-A16 strains isolated in Fukushima from 1983 to 2003 demonstrated three distinct genetically divergent clusters related to HFMD epidemics that occurred from 1984 to 1994 (including the 1985 and 1991 outbreaks), HFMD epidemics from 1987 to 1998 (including the 1988 and 1998 outbreaks), and HFMD epidemics from 1995 to 2003 (including the 1995 and 2002 outbreaks). CV-A16 strains isolated during each period in Fukushima formed a single cluster with those isolated during essentially the same time period in other areas of Japan and in China. Our results demonstrated that prevalent CV-A16 strains causing HFMD in Fukushima, Japan, genetically changed twice during 21 epidemics, and changes were also observed in the CV-A16 strains causing HFMD epidemics in other areas. We concluded that repeated outbreaks of CV-A16-related HFMD in Japan were caused, in part, by the introduction of genetically changed CV-A16 strains, which might be transmitted overseas.

FIG. 1.

Numbers of CV-A16 isolates in Fukushima Prefecture and in Japan between 1983 and 2003. Numbers of CV-A16 isolates in Fukushima (closed circles and solid line) and in Japan (open circles and broken line) are expressed, as reported to the Infectious Disease Surveillance Center in Japan by prefectural and municipal public health institutes through the Japanese infectious agents surveillance program. A, B, and C refer to genogroups designated based on phylogenetic analysis of the VP4 sequences of CV-A16 strains. Solid bars and broken bars indicate HFMD outbreaks and epidemic periods, respectively, due to corresponding genogroups.

FIG. 2.

Phylogram depicting the phylogenetic relationships on the basis of the VP4 sequence among 129 CV-A16 strains isolated in Fukushima from 1983 to 2003. Bootstrap analysis was performed by resampling the data sets 1,000 times. Bootstrap values greater than 70% were considered to be statistically significant for the grouping and were denoted in the figure. Isolated place, strain name, and isolated year were indicated. The GenBank accession number of one isolate to represent isolates with identical sequences is also indicated in parenthesis. CA-A16/G-10/51 is the prototype CV-A16 strain. The VP4 nucleotide sequence of prototype HEV71/BrCr/71 was used as an outgroup in the analysis.

FIG. 3.

Phylogram depicting the phylogenetic relationships on the basis of the VP4 sequence among representative 54 CV-A16 strains isolated in Fukushima and 50 CV-A16 strains isolated in Japan, China, and United Kingdom taken from international databases (GenBank). Bootstrap analysis was performed by resampling the data sets 1,000 times. Bootstrap values greater than 70% were considered to be statistically significant for the grouping and were denoted in the figure. Isolated place, strain name, and isolated year were indicated. GenBank accession numbers of CV-A16 strains isolated in Fukushima and the strains taken from international databases are indicated in parentheses. CA-A16/G-10/51 is the prototype CV-A16 strain. The VP4 nucleotide sequence of prototype HEV71/BrCr/71 was used as an outgroup in the analysis.

FIG.4.

Alignment of the entire VP4 sequences. Common genetic diversities were observed in each genogroup. Nucleotide differences from the prototype CV-A16/G-10/51 strain observed in genogroup A, genogroup A and B, or genogroup A and C are indicated by shading and those in genogroup B, genogroups B and C, or genogroup C are indicated in boxes.

FIG.4.

Alignment of the entire VP4 sequences. Common genetic diversities were observed in each genogroup. Nucleotide differences from the prototype CV-A16/G-10/51 strain observed in genogroup A, genogroup A and B, or genogroup A and C are indicated by shading and those in genogroup B, genogroups B and C, or genogroup C are indicated in boxes.

FIG.4.

Alignment of the entire VP4 sequences. Common genetic diversities were observed in each genogroup. Nucleotide differences from the prototype CV-A16/G-10/51 strain observed in genogroup A, genogroup A and B, or genogroup A and C are indicated by shading and those in genogroup B, genogroups B and C, or genogroup C are indicated in boxes.