Molecular characterization of genotype G6 human rotavirus strains detected in Italy from 1986 to 2009

Group A human rotavirus (HRV) strains with a bovine-like (G6) major outer capsid protein VP7 were first detected in Palermo, Italy, in the late 1980s, and subsequently worldwide. During a 25-year rotavirus surveillance period, additional HRV G6 strains, associated with either a P[9] or P[14] VP4 genotype, have been detected sporadically, but repeatedly, in Palermo. Whether these G6 HRVs were transmitted to humans directly from an animal reservoir or could have circulated at low prevalence in susceptible individuals is uncertain. Upon sequence analyses of the VP7, VP4, VP6, NSP4 and NSP5 gene segments, all the Italian HRV strains displayed a conserved genotype constellation, G6-P[9]/[14]-I2-E2-H3. Intra-genotypic lineages and/or sub-lineages were observed among the various HRV strains, with some lineage/sublineage combinations being retained over time. Interestingly, two epidemiologically unrelated G6P[9] viruses, collected in the same rotavirus season, were found to have a clonal origin. In conclusion, our results indicate not only diverse origin of animal derived G6 HRVs in Palermo but also suggest human-to-human transmission of certain strains.