An Overview of Noroviruses as gastroenteritis viruses in people in all ages

Background and Aim : Noroviruses(NoVs) are recognized as the leading cause of viral acute gastroenteritis in people of all ages worldwide.NoVs are classified within the Caliciviridae family with RNA genome.The genome is organized into ۳ open reading frames (ORFs).ORF۱ encodes a polyprotein,ORF۲ encodes VP۱ and ORF۳ encodes VP۲.Based on sequence differences of the VP۱ protein,NoVs are classified into ۱۰ genogroups(GI-GX) and subclassified into ۴۹ genotypes.The emergence of new recombinant strains are high and these recombinations most frequently occurs between the junction of ORF۱ and ORF۲.The symptoms includes: diarrhea, vomiting, nausea, stomach pain, fever and headache.NoVs are highly infectious and can be spread from person to person through fecal-oral transmission,contaminated food,water,and environmental surfaces.There are no vaccines to prevent norovirus infection,although several candidate vaccines are in clinical and pre-clinical trials.However,WHO highlighted NoVs as a priority for vaccine development,few studies have been conducted in Iran on genetic characteristics and circulating genogroups and genotypes.Methods : In this review,we summarized over ۳۵ different studies on NoVs from ۲۰۱۵ to ۲۰۲۰ in Iran and the rest of the world.The overall protocol is to extract the RNA of virus with special kits and amplify the genome with real-time quantitative RT-PCR, followed by nucleotide sequencing and phylogenetic analysis.Results : According to these studies, ۲۴ of the ۳۵ articles,were included for a norovirus prevalence and genotyping data.The infection causes by norovirus GII is more prevalent than GI.There was a significantly higher proportion of GII.۴ in samples of NoVs.Although in recent years, non-GII.۴ strains such as:GII.۱۷,GII.۳,GII.۶ and GII.۲ have replaced GII.۴ strains in several countries.The prevalence in cases of acute gastroenteritis was estimated at about ۱۸% worldwide.Conclusion : The rapidly expanding infection causes by NoVs shows its contribution with global burden across all settings and age groups. In agreement with previous reports, most infections in these studies, were caused by GII viruses. The prevalence of NoV in European and American countries, because of different feeding patterns may be different with Middle Eastern countries. Although the prevalence of NoV in Iran is lower than other developing countries, promoting public health education and preparation of health care setting for controlling the Norovirus sporadic cases and outbreaks are strongly recommended.