Emergence of norovirus strains: A tale of two genes

Abstract

Noroviruses are a very diverse group of viruses that infect different mammalian species. In humans, norovirus is a major cause of acute gastroenteritis. Multiple norovirus infections can occur in a lifetime as the result of limited duration of acquired immunity and cross-protection among different strains. A combination of advances in sequencing methods and improvements on surveillance has provided new insights into norovirus diversification and emergence. The generation of diverse norovirus strains has been associated with (1) point mutations on two different genes: ORF1, encoding the non-structural proteins, and ORF2, encoding the major capsid protein (VP1); and (2) recombination events that create chimeric viruses. While both mechanisms are exploited by all norovirus strains, individual genotypes utilize each mechanism differently to emerge and persist in the human population. GII.4 noroviruses (the most prevalent genotype in humans) present an accumulation of amino acid mutations on VP1 resulting in the chronological emergence of new variants. In contrast, non-GII.4 noroviruses present co-circulation of different variants over long periods with limited changes on their VP1. Notably, genetic diversity of non-GII.4 noroviruses is mostly related to the high number of recombinant strains detected in humans. While it is difficult to determine the precise mechanism of emergence of epidemic noroviruses, observations point to multiple factors that include host-virus interactions and changes on two regions of the genome (ORF1 and ORF2). Larger datasets of viral genomes are needed to facilitate comparison of epidemic strains and those circulating at low levels in the population. This will provide a better understanding of the mechanism of norovirus emergence and persistence.

Unrevealed genetic diversity of GII Norovirus in the swine population of North East Italy

“…Since the first report of GII NoVs in pigs in the USA, other countries in Europe and Latin America have reported the presence of this genogroup in diseased and healthy pigs 8,14,18,19,25,26 . Detection of GII and GI NoVs in swine fecal samples, retail and imported raw meat samples 7,13,27 , has raised public health concerns about the zoonotic potential of porcine NoVs and the role of swine in the epidemiology of this infection, as a possible source of new viral recombinant strains that can be transmitted directly to humans 7,26,28 . To date, the contribution of swine NoVs to human infections remains unclear and to be elucidated.…”

Diversity of Noroviruses throughout Outbreaks in Germany 2018

“…Antigenic drift variants of GII.4 persist for years until they are replaced by a new variant in a chronological sequential emergence [ 8 ], similar to influenza A viruses (reviewed by G.I. Parra [ 28 ]). Analysis of specific antigenic sites within the capsid protein that interact with human antibodies has given important insights into our understanding how genotype GII.4 strains escape from herd immunity and drive pandemic outbreaks.…”

Metal Nanoparticles: a Promising Treatment for Viral and Arboviral Infections

“…Globally, it is an established etiological agent in acute gastroenteritis outbreaks affecting all age groups. The infection causes a sudden onset of vomiting, diarrhea, abdominal pain, and cramps after contact with contaminated food or infected individuals [151]. Norovirus can be life-threatening to children, especially undernourished children from developing countries [152], infants, older adults, and immunocompromised individuals [151].…”

“…The infection causes a sudden onset of vomiting, diarrhea, abdominal pain, and cramps after contact with contaminated food or infected individuals [151]. Norovirus can be life-threatening to children, especially undernourished children from developing countries [152], infants, older adults, and immunocompromised individuals [151]. There are no clinically approved antivirals and vaccines for norovirus infections [153] since the challenge is that the virus presents with a vast genetic diversity, with over thirty different genotypes infecting humans [151].…”