Norovirus (NoV) is one of the leading causes of acutegastroenteritis and responsible for more than 212,000 deaths annually worldwide.Currently,there is no vaccine to prevent NoV diarrhea. Development of a suitable vaccineis challenging since the viruses are difficult to culture and undergo rapidgenetic diversification through antigenic shift. Bangladesh is a denselypopulated low-income country with high burden of diarrheal diseases.
Despite therecognition of NoV as a leading cause of gastroenteritis, the virus is leaststudied and poorly understood in low-income countries. This study aimed toelucidate genomic features of NoVs identified in hospitalized patients.International Centre for Diarrhoeal Disease Research,Bangladesh (icddr,b) has been running its hospital based diarrhea etiologysurveillance for last 40 years but NoV has never been included to thissurveillance.
During 2015-16, we tested NoV RNA in a sub-sample of stools fromhospitalized patients by using multiplex one step real-time RT-PCR. Genotypingand recombination of NoV capsid and polymerase genes were determined by sangersequencing.Overall, NoV RNA was identified in 83 (18%) out of 450stool specimens. Majority of the NoV positives were genogroup GII (89%) andremaining were GI (7%) and mixed GI and GII (4%). Among 56 NoV strains whichwere successfully genotyped, more than half were recombinants consisting ofdifferent genotypes of GII which include GII.P16/GII.
4 (16%); GII.P16 /GII.3 (16%);GII.P16/GII.
2 (5%); GII.Pe/GII.17 (4%); GII.P7/GII.6 (7%); GII.Pm/GII.1 (5%);and GII.Pg/GII.
12 (2%). Other major genotypes were GII.P4/GII.4 (27%) andGII.P7/GII.6 (7%).
No recombinant GI was identified. Remarkably, higherproportion of recombinant strains (90%, 19/21) were detected in 2016 comparedto 2015 (34%, 12/35). Our phylogenetic analysis reveals that most of theserecombination events might be due to the incorporation of the polymeraseGII.P16 component into the mainstream of NoV strains i.e. GII.2, GII.3, andGII.
4 resulting in generation of the emerging strains.Our study reveals high incidence of recombinant NoV genotypeswhich were facilitated by recombination between capsid and polymerase genesfrom distinct GII genotypes. Although their pandemic potential is yet to beinvestigated, the identification of the emerging variants as well ascontemporary global strains in this study is an illustration of the enormousdiversity of NoV strains in Bangladesh.