Genetic analyses of the fusion protein genes in human parainfluenza virus types 1 and 3 among patients with acute respiratory infections in Eastern Japan from 2011 to 2015.

PURPOSE: To genetically explorer the fusion protein gene (F) in human parainfluenza virus type 1 (HPIV1) and type 3 (HPIV3) strains, we analyzed them in the patients with acute respiratory infections (ARI) in Eastern Japan from 2011 to 2015.

METHODOLOGY: We constructed phylogenetic trees based on the HPIV and HPIV3 F gene using the maximum likelihood method and conducted p-distance, and selective pressure analyses. We also predicted the linear epitopes of the protein in the prototype strains. Furthermore, we mapped the amino acid substitutions of the proteins.Results/Key findings:Nineteen strains of HPIV1 and 53 strains of HPIV3 were detected among the clinical ARI cases. The phylogenetic trees indicated that the HPIV1 and HPIV3 strains were classified into clusters II and III, and cluster C, respectively. The p-distance values of the HPIV1 and HPIV3 F genes were <0.03. Two positive selection sites were inferred in the HPIV1 (aa8 and aa10), and one positive selection site was inferred in the HPIV3 (aa108); but over 10 negative selection sites were inferred. Four epitopes were predicted for the HPIV1 prototype strains, while five epitopes were predicted for the HPIV3 prototype strain. A positive selection site (aa108), or the HPIV3 F protein was involved in the predicted epitope. Additionally, we found that an amino acid substitution (R73K) in the LC76627 HPIV3 strain presumably may affect the resistance to neutralization by antibodies.

CONCLUSION: The F gene of the HPIV1 and HPIV3 were relatively well conserved in the Eastern part of Japan during the investigation period.