Evolutionary Studies on the Coxsackievirus A-24 Variants Causing Acute Hemorrhagic Conjunctivitis with Emphasis on the Recent Outbreak of 2023 in India

Acute Hemorrhagic Conjunctivitis (AHC) is primarily caused by viral infections, with Coxsackievirus A-24v (CV-A24v) being a significant culprit. Enteroviruses, including CV-A24v, are responsible for global AHC outbreaks. Over time, CV-A24v has evolved, and genotype IV (GIV) has become the dominant strain. This study focused on examining the genetic features and evolutionary trends of CV-A24v responsible for the recent AHC outbreak of 2023 in India. Researchers isolated viral strains from ocular swabs and confirmed the presence of CV-A24v using reverse transcriptase quantitative PCR (RT-qPCR) and whole-genome sequencing. Genomic comparisons between isolates of 2023 and those from a previous outbreak in 2009 were conducted. Phylogenetic analysis revealed that the 2023 isolates formed a distinct cluster within GIV-5 and were related to recent strains from China and Pakistan. The older Indian isolates from 2009 grouped with GIV-3. New subclades, GIV-6 and GIV-7, were also identified in this study, indicating the diversification of CV-A24. Molecular clock and phylogeographic analysis traced the virus's circulation back to the 1960s, with the common ancestor likely to have originated in Singapore in 1968. The 2023 Indian strains probably originated from Thailand around 2014, with subsequent spread to China and Pakistan. This study concluded that the 2023 outbreak was caused by a genetically distinct CV-A24v strain with nine mutations, underlining the virus's ongoing evolution and adaptations and offering valuable insights for future outbreak control.