Genetic variability of VP7, VP4, VP6 and NSP4 genes of common human G1P[8] rotavirus strains circulating in Italy between 2010 and 2014

Group A rotaviruses (RVA) are the leading cause of acute gastroenteritis (AGE) in young children worldwide. The RVA outer capsid layer is composed of the VP7 and VP4 proteins. The VP7 (G-type) and VP4 (P-type) genotypes are the basis for the binary RVA nomenclature. At least 27 G-types and 37 P-types of RVA are currently known, but most of human infections are related to the five major genotypes G1P[8], G2P[4], G3P[8], G4P[8], and G9P[8].Every year G1P[8] strains cause approximately 50% of all symptomatic RVA infections reported in children in Italy. Fifteen G1P[8] RVA strains identified in different areas of Italy between 2010 and 2014 were selected. Strains were subjected to nucleotide sequencing of the VP7, VP4, VP6 and NSP4 genes to investigate their genetic variability with respect to geographic area and date of detection. Phylogenetic analyses showed that the 15 G1P[8] RVA strains belonged to two different lineages for both the VP7 and NSP4 genes, and showed some intra-lineage diversity in VP4 and VP6 genes. Similarities between strains correlated by either area or date of detection were also evaluated. The results obtained by phylogenetic analyses were confirmed analyzing the deduced amino acid sequences of the VP7, VP4, VP6 and NSP4 proteins of the G1P[8] RVA strains, detecting several substitutions in all proteins. The genetic variability observed between common G1P[8] RVAs highlights the constant evolution of the RVA genome through random point mutations (genetic drift) and intra-genotype reassortment (genetic shift). The evolution and diversity of the G1 RVA strains observed in this study can be related to the naturally acquired herd immunity, which represents the main mechanism of selective pressure in Italy, where mass anti-rotavirus vaccination was missing during the years of the study.