Molecular identification of coxsackievirus A24 variant,isolated from an outbreak of acute hemorrhagic conjunctivitis in Singapore in 2005

Summary An outbreak of acute hemorrhagic conjunctivitis (AHC) was reported in Singapore military camps in the year 2005. A total of 103 conjunctival swab specimens were collected from military personnel diagnosed clinically with AHC. PCR testing on these conjunctival specimens revealed the presence of an enterovirus, and this was confirmed by virus isolation. Molecular typing using a partial VP1 gene confirmed a variant of coxsackievirus A24 (CA24v) as the most likely etiological agent for the outbreak. Full-length genome sequencing was carried out on 2 selected virus strains, DSO-26SIN05 and DSO-52SIN05. Sequence comparison and phylogenetic analyses of the VP4, VP1 and 3Cpro gene regions were performed, clustering the Singapore CA24v strains with viruses originating from Asia in the post-2000 era. In addition, we report evolution rates of 4.2 × 10⁻³ and 1.0 × 10⁻³ nucleotide/year, respectively, for the VP4 capsid and 3Cpro gene regions. Our result shows a focal evolutionary point around 1965–1966, suggesting that the CA24v virus has been evolving constantly since its emergence in Singapore, nearly 40 years ago.