Genetic characteristics of the coxsackievirus A24 variant causing outbreaks of acute hemorrhagic conjunctivitis in Jiangsu, China, 2010

Abstract

During September 2010, an outbreak of acute hemorrhagic conjunctivitis reemerged in Jiangsu, three years after the nationwide epidemic in China in 2007. In total, 2409 cases were reported, 2118 of which were reported in September; 79.8% of those affected were students or teachers, with a median age of 16 years. To identify and demonstrate the genetic characteristics of the etiological agent, 52 conjunctival swabs were randomly collected from four different cities. After detection and isolation, 43 patients were positive for coxsackievirus A24 variant according to PCR and 20 according to culture isolation. Neither adenovirus nor EV70 was detected. A phylogenetic study of the complete 3Cpro and VP1 regions showed that the Jiangsu isolates clustered into a new lineage, GIV-C5, with two uniform amino-acid mutations that distinguished them from all previous strains. Another new cluster, GIV-C4, formed by Indian isolates from 2007 and Brazilian isolates from 2009, was also identified in this study. Interestingly, our isolates shared greatest homology with the GIV-C4 strains, not with the isolates that were responsible for the nationwide acute hemorrhagic conjunctivitis epidemic in China in 2007. Although all our isolates were closely related, they could be differentiated into two subclusters within GIV-C5. In conclusion, our study suggests that a new cluster of coxsackievirus A24 variant that had already evolved into diverse strains was associated with the acute hemorrhagic conjunctivitis outbreaks in Jiangsu in September 2010. These viruses might have originated from the virus isolated in India in 2007, rather than from the epidemic strains isolated in China in 2007.

Figure 1. Distribution of the reported AHC cases in Jiangsu Province during the outbreak of September 2010.

Figure 2. Phylogenetic analysis based on the 549-nucleotide 3Cpro gene of CA24v.

All Jiangsu CA24v isolates identified in this study, marked with black triangles, were compared with strains available in GenBank. Strains for which the complete sequences of both the 3Cpro and VP1 regions were available are indicated with **. The MEGA 4.0 software was used for the phylogenetic analysis. The stability of the nodes was assessed using neighbor-joining cluster analysis with 1000 bootstrap replications, and only bootstrap values >70% are shown at the nodes.

Figure 3. Phylogenetic analysis based on the 915-nucleotide VP1 gene of CA24v.

All Jiangsu CA24v isolates identified in this study, marked with black triangles, were compared with strains available in GenBank. Strains for which the complete sequences of both the 3Cpro and VP1 regions were available are indicated **. The MEGA 4.0 software was used for the phylogenetic analysis. The stability of the nodes was assessed using neighbor-joining cluster analysis with 1000 bootstrap replications, and only bootstrap values >70% are shown at the nodes.