Noroviruses are non-enveloped (naked) viruses with a positive, single-stranded RNA genome. They are the main cause of acute nonbacterial human gastroenteritis. Transmission of the virus occurs by food or by person to person via a fecal-oral route.
Noroviruses belong to the family Caliciviridae and are grouped into five genogroups ranging from GI through GV. These groups are further divided into at least 34 genotypes. GI and GII genogroups are the primary cause of human disease by noroviruses. Most outbreaks are caused by GII.4 strains.
Viruses with RNA as their genetic material can quickly adapt to changing environments and conditions. RNA viruses demonstrate genetic variation by mutation (due to the high error rates of viral polymerases that replicate their genomes), recombination, and reassortment. This ability to rapidly adapt to changing conditions leads to the emergence of new strains, often leading to an increase in outbreak activity. New GII.4 strains have been emerging every 2–3 years, replacing previously predominant GII.4 strains.
In March 2012, a new GII.4 norovirus strain, GII.4 Sydney, was identified in Australia and has since caused acute gastroenteritis outbreaks in multiple countries. During September–December 2012, a total of 141 (53%) of the 266 norovirus outbreaks were reported to CaliciNet—an electronic laboratory surveillance network maintained by the CDC—were caused by GII.4 Sydney. The other reported outbreaks were caused by 10 different GI and GII genotypes— including GII.4 New Orleans, which emerged in 2009.
The preferred method of detection of noroviruses is through molecular assays. Norovirus is detected by our FDA-cleared xTAG® Gastrointestinal Pathogen Panel (GPP). This assay is a multiplexed nucleic acid test intended for the simultaneous qualitative detection and identification of multiple viral, parasitic, and bacterial nucleic acids in human stool specimens from individuals showing signs and symptoms of infectious colitis or gastroenteritis.
Emerging noroviruses present an ongoing challenge to methods used to detect noroviruses. How do you know for sure that your norovirus assay will detect these emerging strains?
Norovirus primer sequences in our GPP panel are queried against the sequences of emerging strains, including GII.4 Sydney and GII.4 New Orleans, as they become available in the sequence databases. Our norovirus primers show 100% alignment to these 2 strains. A clinical specimen that was confirmed positive for GII.4 Sydney by a public health lab tested positive for Norovirus GII by the GPP panel.
Proactive monitoring of emerging strains will ensure consistent and reproducible detection of norovirus year after year by our GPP assay.
To learn more about noroviruses, see our Norovirus Infectious Information Sheet and the references below.
References:
CDC. Notes from the field: Emergence of new norovirus strain GII.4 Sydney—United States, 2012. Morbidity and Mortality Report Weekly Report. January 25, 2013. 62(03): 55-55.
Karst, S., M. Pathogenesis of noroviruses, emerging RNA virues. Viruses. 2010 March; 2(3): 748–781.
van Beek J, Ambert-Balay K, Botteldoorn N, Eden JS, Fonager J, Hewitt J, Iritani N, Kroneman A, Vennema H, Vinjé J, White PA, Koopmans M, on behalf of NoroNet. Indications for worldwide increased norovirus activity associated with emergence of a new variant of genotype II.4, late 2012. Euro Surveill. 2013;18(1):pii=20345.
Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20345
Also, see these recent Norovirus communications for more information:
http://www.ncbi.nlm.nih.gov/pubmed/23514289
http://afludiary.blogspot.com/2013/03/cdc-norovirus-now-leading-cause-of.html
http://www.cdc.gov/media/releases/2013/p0321_norovirus_children.html