Norovirus (formerly Norwalk agent) is an RNA virus (taxonomic family Caliciviridae) that causes approximately 90% of epidemic nonbacterial outbreaks of gastroenteritis around the world, and may be responsible for 50% of all foodborne outbreaks of gastroenteritis in the United States.
Norovirus affects people of all ages. The viruses are transmitted by fecally contaminated food or water, by person-to-person contact, and via aerosolization of the virus and subsequent contamination of surfaces.
Ligocyte announced in 2007 that it was working on a vaccine and had started phase 1 trials. As of 2011, a monovalent nasal vaccine has completed phase I/II trials, while bivalent intramuscular and nasal vaccines are at earlier stages of development.
Routine protocols to detect norovirus (norovirus RNA) in clams and oysters by reverse transcription polymerase chain reaction are being employed by governmental laboratories such as the FDA in the USA. However, routine methods to detect the virus on other food items are not readily available because of the variable nature of different food items affecting concentration and extraction of the virus and presence of factors that make polymerase chain reaction analysis techniques ineffective.
Epidemiological data from developing countries about the importance of norovirus in pediatric diarrhea are limited. Recently, in Nicaragua, it has been observed that norovirus is responsible for 11% of the diarrhea cases occurring in children less than five years of age at community level and 15% of the moderate to severe cases requiring intravenous rehydration.
This transmission electron micrograph (TEM) revealed some of the ultrastructural morphology displayed by norovirus virions, or virus particles.
In the Guangdong province of the People's Republic of China, the Provincial Health Department said on December 17, 2010, that it had confirmed 429 cases of norovirus infection in the November 2010 outbreak in Conghua, Guangzhou, but no one died from it.
Outbreaks of norovirus infection often occur in closed or semiclosed communities, such as long-term care facilities, overnight camps, hospitals, prisons, dormitories, and cruise ships, where the infection spreads very rapidly either by person-to-person transmission or through contaminated food. Many norovirus outbreaks have been traced to food that was handled by one infected person.
Norovirus is rapidly inactivated by either sufficient heating or by chlorine-based disinfectants, but the virus is less susceptible to alcohols and detergents, as it does not have a lipid envelope.
The norovirus was originally named the "Norwalk agent" after Norwalk, in the United States, where an outbreak of acute gastroenteritis occurred among children at Bronson Elementary School in November 1968.
In 1972, electron microscopy on stored human stool samples identified a virus, which was given the name "Norwalk virus." Numerous outbreaks with similar symptoms have been reported since. The cloning and sequencing of the Norwalk virus genome showed these viruses have a genomic organization consistent with viruses belonging to the family Caliciviridae. The name was shortened to "''norovirus''" after being identified in a number of outbreaks on cruise ships and receiving attention throughout the United States. The name "norovirus" (''Norovirus'' for the genus) was approved by the International Committee on Taxonomy of Viruses in 2002.
In addition to "Norwalk agent" and "Norwalk virus," the virus previously has been called "Norwalk-like virus," "small, round-structured viruses" (SRSVs), and "Snow Mountain virus."
Common names of the illness caused by noroviruses still in use include "winter vomiting disease," "winter vomiting bug," "viral gastroenteritis," and "acute nonbacterial gastroenteritis." It also colloquially is known as "stomach flu," but this actually is a broad name that refers to gastric inflammation caused by a range of viruses and bacteria.
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