A molecular epidemiological study of human respiratory syncytial virus in Croatia, 2011-2014

Human respiratory syncytial virus (HRSV) causes common respiratory tract infections in infants, young children and the elderly. The diversity of HRSV strains circulating in Croatia was investigated throughout a period of four consecutive years from March 2011-March 2014. The analysis was based on sequences from the second hypervariable region of the G gene. A predominance of HRSV group A was observed in the first three years of the study, while group B became slightly predominant during the first few months of 2014. Overall, 76% of viruses belonged to group A including the genotypes NA1, ON1 and GA5. NA1 was by far the most common genotype within group A in 2011-2013; however, only ON1 and a few GA5 viruses were detected in the first three months of 2014. The majority of group B strains were of genotype BA9 (97%), and a few BA10 genotypes were detected. BA9 had the highest substitution rate of all the detected genotypes, followed by ON1. Multiple analyses showed that HRSV group A strains were more diverse than group B strains. Gly at residue 232 (previously described to be specific for ON1) was also detected in three NA1 strains, which were phylogenetically placed on separate branches within the NA1 genotype. For all genotypes, the diversity was higher at the amino acid level than at the nucleotide level, although positive selection of mutations was shown for only a few sites using four different methods of codon-based analysis of selective pressure. More codons were predicted to be negatively selected. The complexity of the HRSV pools present during each epidemic peak was determined and compared to previous epidemiological data. In addition to presenting genetic versatility of HRSV in this geographic region, the collected sequences provide data for further geographical and temporal comparative analyses of HRSV and its evolutionary pathways.