Variant GII.4 noroviruses in Italian children

Abstract

Objectives: Among human noroviruses (NoVs), a few genogroup II strains of genotype 4 (GII.4) are dominant worldwide. GII.4 NoVs evolve rapidly and in 2006 two new epidemic variants have been identified. To investigate the circulation of GII.4 NoV variants in Italy a sequence analysis was performed on NoV strains obtained from children hospitalized for sporadic viral gastroenteritis in Palermo. Methods: A total of 465 faecal specimens were collected from children (< 5 years) hospitalized from January 2005 to December 2006. The presence of NoVs was detected by RT-PCR using primers JV12/JV13, targeting the region A of the RNA-dependent RNA-polymerase (RdRp) gene. NoV strains were genotyped by RdRp restriction fragment length polymorphism (RFLP) with XmnI, BstXI and sequence analysis of region A and of the ORF1/ORF2 junction region obtained with primer pair GIISKR/GIIFBN1-2-3. Phylogenetic analysis including isolates from the 2002-2004 surveillance was carried out using the software MEGA version 4. Results: Viral gastroenteritis surveillance resulted in the detection of NoV strains in 20.9% of the patients admitted to hospital. RFLP and sequence analysis of the RdRp gene allowed to successfully characterise 59 NoV strains. Eighty-one % of the strains were characterized as GII.4, 14% as GIIb/Hilversum and 5% as GI.1. Phylogenetic analysis of region A and of the ORF1/ORF2 overlapping region of the GII.4 strains recovered in Palermo in the years 2002-2006 revealed the sequential emergence of four variants, GII.4 2002, 2004, 2006a and 2006b. The variant GII.4 2006a was detected in June and July, 2006, while the variant 2006b first appeared in August, 2006, becoming predominant thereafter. Conclusion: The high detection rate of GII.4 NoVs in Italian children with gastroenteritis confirms their prominent role as human enteropathogens. At least four distinct GII.4 NoV variants appeared in Palermo in the last years and their dynamics of replacement and circulation in 2005-2006 appear to have matched the temporal pattern observed in Europe during the same period.