Circulation of GII.4 norovirus strains in children

Abstract

Background: GII.4 norovirus strains have caused the majority of norovirus outbreaks and sporadic cases globally since the mid-1990s. New norovirus GII.4 strains emerge every 2–4 years, circulate widely, and replace older variants. Novel variants emerge through a combination of recombination, genetic drift, and selection possibly driven by population immunity. Variants of GII.4 viruses have caused all the 6 pandemics of acute gastroenteritis caused by noroviruses in the last 2 decades. Methods and materials: In order to study the diversity of circulating norovirus GII.4 strains in Vellore (south India) over a 13 years period, stool samples collected from children <5 years hospitalized for acute watery diarrhea at Christian Medical College, Vellore, from December 2005 to December 2018, were tested for norovirus GI and GII by multiplex one-step real-time PCR (qRT-PCR). Norovirus positive samples were genotyped by performing conventional PCR that amplified the ORF1-ORF2 junction region, followed by Sanger sequencing, and sequence data analysis of the ORF2 (major capsid protein VP gene). Results: A total of 3303 stool samples were tested, of which 13.7% (451/3303) were positive for norovirus. Of the 451 samples positive for norovirus by qRT-PCR, 69.8% (315/451) were genotyped (19 GI and 296 GII genotypes). 63.9% (189/296) of the GII positive samples were GII.4 genotype. During 2005–2006, GII.4 Yerseke (60%) was the most common GII.4 variant, followed by GII.4 Hunter (33.3%). During 2007, GII4 Den Haag (55%) emerged as the predominant strain, followed by GII.4 Osaka (35%). During 2008, GII.4 Osaka was the most common (81.8%), which was replaced by GII.4 New Orleans (50%) in 2009. GII.4 New Orleans continued to be the most common variant in 2011. In 2012, GII.4 Sydney (42.9%) emerged as the most common GII.4 variant, along with GII.4 New Orleans (42.9%). During the successive years from 2013 to 2018, GII.4 Sydney remained the predominant GII.4 variant in Vellore. Conclusion: The circulation of norovirus GII.4 variants in our setting is similar to that reported globally.