Predominance of Recombinant Norovirus Strains in Greece, 2016-2018

GII.4 noroviruses have caused the overwhelming majority of norovirus-related gastroenteritis cases during the past two decades. However, a trend towards the emergence of new genotypes and novel GII.4 variants provided the impetus to explore further the changing patterns in norovirus epidemiology during the present study. Genotyping of 60 norovirus strains detected during a period of 33 months (January 2016-October 2018) was performed on the basis of the capsid VP1-coding ORF2 gene sequence. All norovirus strains detected were classified into seven genotypes, six of which belonged to genogroup GII. GII.2 was the dominant genotype till February 2017, whereas GII.4 prevailed thereafter. Most of the GII.4 strains were of the Sydney_2012 variant, whereas five strains could not be classified. Further recombination analysis at the ORF1/ORF2 gene junction revealed that 23 out of 24 strains were recombinant, thereby showcasing the significant role of genetic recombination in norovirus evolution and epidemiology. Continuous genomic surveillance and molecular characterization are essential for tracking norovirus evolution, which could contribute to the elucidation of new aspects of virus-host interactions that potentially affect host morbidity and epidemiology.