Norovirus , sometimes referred to as winter insects, , is the most common cause of gastroenteritis. Infection is characterized by diarrhea, vomiting, and abdominal pain. Blood usually does not exist. Fever or headache can also occur. It usually develops 12 to 48 hours after exposure. Recovery usually occurs within 1 to 3 days. Complications may include dehydration.
The virus usually spreads through the fecal-oral route. This may be with contaminated food or water or person-to-person contact. It can also spread through contaminated surfaces or through the air. Risk factors include unhealthy food preparation. Diagnosis is generally based on symptoms. Confirmation tests can be performed for public health purposes.
Prevention involves proper hand washing and disinfection of contaminated surfaces. Alcohol-based hand sanitizers are less effective. The vaccine does not exist. No special treatment. Efforts involve supportive care such as drinking enough fluids or intravenous fluids. Oral rehydration solution is the preferred liquid to drink.
Norovirus produces about 685 million cases of illness and 200,000 deaths globally per year. This is common in developed and developing countries. Those under the age of five are most often affected and in this group produce about 50,000 deaths in developing countries. Illness is more common in winter. This often happens in outbreaks, especially among those living close by. In the United States the cause is about half of foodborne disease outbreaks. The disease is named after Norwalk, Ohio, where an outbreak occurred in 1968.
Video Norovirus
Signs and symptoms
Norovirus infection is characterized by nausea, vomiting, watery diarrhea, abdominal pain, and in some cases, loss of appetite. A person usually develops symptoms of gastroenteritis 12 to 48 hours after exposure to norovirus. General lethargy, weakness, muscle aches, headache, and mild fever may occur. The disease is usually self-limiting, and severe disease is rare. Although having a norovirus can be unpleasant, it is usually harmless and the bulk of the contracts make full recovery in two to three days.
Maps Norovirus
Virology
Transmission
Norovirus is passed from person to person (62-84% of all outbreaks are reported) and indirectly through contaminated water and food. They are highly contagious, and fewer than twenty viral particles can cause infection (some studies show at least five). Transmission can become aerosol when they are attacked by vomiting, and can be aerosolized by flush toilets when vomiting or diarrhea is present; Infection may occur after eating food or breathing air near episodes of vomiting, even if cleansed. Viruses continue to be shed after symptoms subside and shedding can still be detected a few weeks after infection.
Vomiting, in particular, transmits infections effectively, and seems to allow air transmission. In one incident, someone who spewed an infection spread in a restaurant, suggesting that many cases of unexplained food poisoning may have their source in vomit. In December 1998, 126 people ate at six tables; a woman vomiting to the floor. The staff was quickly cleaned, and people kept eating. Three days later others began to fall ill; 52 people reported various symptoms, from fever and nausea to vomiting and diarrhea. The cause is not immediately identified. The researchers planned a seating arrangement: more than 90% of the people on the same table with the sick woman were reportedly sick. There is a direct correlation between the risk of infection of people at other tables and how close they are to sick women. More than 70% of visitors at adjacent tables get sick; at the table on the other side of the restaurant, the attack rate is still 25%. The plague was associated with Norwalk virus (norovirus). Other cases of infection with vomiting were then identified.
In one outbreak at the international Scout jamboree in the Netherlands, everyone with gastroenteritis infected an average of 14 people before an increase in hygiene measures was put in place. Even after these new measures are enacted, the sick person still infects an average of 2.1 others. A US CDC study of 11 outbreaks in New York State listed the manner of person-to-person transmission in seven outbreaks, transmitted by food in two, transmitted by water in one, and one unknown. Source of water-borne outbreaks may include water from city supplies, wells, recreational lakes, swimming pools and ice machines.
Shellfish and salad ingredients are the foods most commonly involved in the norovirus outbreak. Consumption of unfilled shellfish - below 75 ° C (167 ° F) - poses a high risk for norovirus infection. Foods other than shellfish can be contaminated by an infected food handler. Many of the norovirus outbreaks have been traced to foods handled by one infected person.
Classification
Noroviruses (NoV) is a genetically diverse group of positive-sense RNAs, viruses without family enrichopes Caliciviridae . According to the International Committee on Virus Taxonomy, the genus Norovirus has one species, called Norwalk virus . Serotypes, strains and isolates include:
- Norwalk virus
- Hawaiian Virus
- Snow Mountain virus
- Mexican virus
- Desert Shield virus
- The Southampton virus
- Lordsdale virus
- Wilkinson Virus
Noroviruses are usually isolated in cases of acute gastroenteritis belonging to two genogroups: genogroup I (GI) including Norwalk virus, Desert Shield virus and Southampton virus; and II (GII), which includes the Bristol virus, the Lordsdale virus, the Toronto virus, the Mexican virus, the Hawaiian virus, and the Snow Mountain virus.
Genetic noroviruses can be classified into five different genogroups (GI, GII, GIII, GIV, and GV), which can be subdivided into different genetic or genotype groups. For example, genogroup II, the most common human genogroup, currently contains 19 genotypes. Genogroups I, II and IV infect humans, while genogroup III infects bovine species, and genogroup V has recently been isolated in mice.
Most noroviruses that infect humans include genomes GI and GII. Noroviruses of Genogroup II, genotype 4 (abbreviated as GII.4) are responsible for the majority of outbreaks of adult gastroenteritis and often sweep across the world. Recent examples include US95/96-US strains, linked to global outbreaks in the mid to late 1990s; Farmington Hills virus-related outbreaks in Europe and the United States in 2002 and in 2004; and Hunter viruses that are associated with outbreaks in Europe, Japan and Australasia. In 2006, there was a large increase in the worldwide NoV infections. Reports have shown an association between human histo-blood group antigen expression (HBGAs) and susceptibility to norovirus infection. Studies have shown the norovirus viral capsid may have evolved from human HBGA selective pressures.
A 2008 study showed that MDA-5 protein may be a major immune sensor that detects the presence of norovirus in the body. Some people have a common variation of MDA-5 genes that can make them more susceptible to norovirus infection.
A 2010 study suggested a specific genetic version of norovirus (which can not be distinguished from other virus types using standard antibody tests) interacts with specific mutations in the ATG16L1 gene to help trigger a symptomatic Crohn's disease in mice that have been exposed to a chemical that causes intestinal injury similar with the process in humans. (There is another similar way to such a disease happening like this, and this study alone does not prove that noroviruses cause Crohn in humans).
Structure
The virus in Norovirus is not enveloped, with icosahedral geometry. Capsid diameter varies greatly, from 23-40 nm in diameter. The larger capsids (38-40m) show symmetry T = 3 and consist of 180 VP1 proteins. The small capsule (23 nm) shows symmetry T = 1, and is composed of 60 VP1 proteins. Viral particles exhibit amorphous surface structures when visualized using an electron microscope.
Noroviruses contain a linear, non-segmented, linear, positive ration of about 7.5 kbp, encode large polyproteins split into six smaller non-structural proteins (NS1/2 to NS7) by protease-like 3C virus (NS6), structural proteins (VP1) of about 58 ~ 60 kDa and minor capsid protein (VP2).
The most variable region of the viral capsid is the P2 domain, which contains antigen-presentation sites and carbohydrate receptor binders.
Estimated rate of mutation (1.21 ÃÆ' - 10 -2 to 1.41 ÃÆ' - 10 -2 per site per year) in this virus is even higher than with other RNA viruses.
In addition, the recombination hotspot is at the ORF1 - ORF2 junction (VP1).
Life cycle
Virus replication is cytoplasm. Entry to the host cell is achieved by attachment to the host receptor, which mediates endocytosis. Replication follows a positive RNA virus replication model. Transcription of RNA-positive stranded virus is a method of replication. The translation takes place with a leaked scan and RNA termination reactivation. Humans and other mammals act as natural hosts. The transmission route is fecal-oral and contamination.
Pathophysiology
When a person becomes infected with norovirus, the virus is replicated in the small intestine. After about one to two days, symptoms of norovirus infection may occur. The main symptom is acute gastroenteritis that develops between 12 and 48 hours after exposure, and lasts for 24-72 hours. The disease is usually self-limiting, and is characterized by nausea, strong vomiting, watery diarrhea, and abdominal pain, and in some cases, loss of appetite. General lethargy, weakness, muscle aches, headache, cough, and mild fever may occur.
Severe disease is rare; Although people are often treated in emergency rooms, they are rarely hospitalized. The number of deaths caused by norovirus in the United States is estimated at about 300 each year, with most occurring in very young people, the elderly, and people with weakened immune systems. Symptoms can be life-threatening in these groups if dehydration or electrolyte imbalance is ignored or untreated.
Diagnosis
Specific diagnoses of norovirus are routinely made by polymerase chain reaction (PCR) or quantitative PCR tests, which give results within hours. This test is very sensitive and can detect at least 10 virus particles.
Tests such as ELISA that use antibodies against a strand of norovirus strain are commercially available, but lack specificity and sensitivity.
Due to the lack of specific therapy, the need for expensive diagnostic stools is questioned by experts if norovirus gastroenteritis has been detected in the environment.
Prevention
After infection, immunity to the same virus strain - genotype - protects against reinfection for 6 months to 2 years. This immunity does not fully protect against infection with other diverse viral genotypes.
In Canada, norovirus is a disease that should be reported. In the UK not informed, and the same applies in the US.
Hand wash and disinfectant
Hand washing with soap and water is an effective method for reducing the transmission of noroviruses. Rubbing alcohol (> = 62% ethanol) can be used in addition, but less effective than hand washing, because norovirus does not have lipid envelope virus. The surface in which the norovirus particles can be present is cleaned with a solution of 1.5% to 7.5% of household bleach in water, or another effective disinfectant against norovirus.
Healthcare facilities
In a health care setting, prevention of nosocomial infections involves routine cleaning and terminals. Non combustible alcohols in CO 2 systems are used in health care settings where medical electronics will be adversely affected by aerosol chlorine or other caustic compounds.
In 2011, the Centers for Disease Control and Prevention (CDC) published a clinical practice guide that addresses strategies for the prevention and control of the outbreak of norovirus gastroenteritis in health care settings. Based on a systematic review of published scientific studies, these guidelines present 51 specific evidence-based recommendations, organized into 12 categories: 1) patient precautions and isolation, 2) hand hygiene, 3) patient transfer and ward closure, 4) food handlers in health care, 5) diagnostics, 6) personal protective equipment, 7) environmental cleanup, 8) leave and staff policies, 9) visitors, 10) education, 11) active case discovery, and 12) communications and notices. It also identifies eight high-priority recommendations, and suggests areas that require future research.
Vaccine trial
Ligocyte announced in 2007 that they are working on a vaccine and have started a phase 1 trial. The company has been taken over by Takeda. In 2011, monovalent nasal vaccines have completed phase I/II trials, while intramuscular vaccines and bivalent noses are at an early stage of development. Both vaccines rely on the use of virus-like particles made from the norovirus capsid protein to mimic the external structure of the virus. Since there is no RNA in this particle, it is unable to reproduce and can not cause infection.
Perseverance
Noroviruses can survive for long periods beyond the human host depending on surface and temperature conditions: it can last for weeks on hard surfaces, and up to twelve days on contaminated fabrics, and can last for months, even probably years in contaminated water still. A 2006 study found the virus remained on the surface used for food preparation seven days after contamination.
Detection in food
Routine protocols for detecting norovirus in oyster and oyster with reverse polymerase chain transcription reactions are being used by government laboratories such as the Food and Drug Administration (FDA) in the United States.
Treatment
There is no specific drug to treat people with norovirus disease. Norovirus infection can not be treated with antibiotics because it is not a bacterial infection. Treatment aims to avoid complications with measures such as dehydration management caused by fluid loss in vomiting and diarrhea, and to reduce symptoms using antiemetics and antidiarrheal.
Epidemiology
Noroviruses account for about 18% of all cases of acute gastroenteritis worldwide. This is relatively common in developed countries and in developing countries low mortality (20% and 19% respectively) compared to developing countries with high mortality (14%). Proportionately cause more disease in people in the community or in outpatient hospitals (24% and 20% respectively) than in hospitalized patients (17%) of whom other causes are more common.
The age and appearance of new norovirus strains do not seem to affect the proportion of gastroenteritis caused by norovirus.
Norovirus is a common cause of epidemic of gastroenteritis on cruise ships. The US Centers for Disease Control and Prevention through the records of the Ship Sanitation Program and investigating outbreaks of gastrointestinal diseases - mostly caused by noroviruses - on cruises with US and foreign travel plans; there are 12 by 2015, and 10 from 1 January to 9 May 2016. Outbreaks can affect more than 25% of passengers, and a smaller proportion of crew members.
Human genetics
Non-functional FUTOSyltransferase FUT2 provides high protection from the most common GIG.4 norovirus.4. Functional FUT2 Fucosyltransferase transfers fucose sugar to Histo-ABO blood group ends (H) precursors in gastrointestinal cells and salivary glands. The resulting ABH antigen is considered to act as a receptor for the human norovirus. The homozygous carriers of all nonsense mutations in the FUT2 gene are called non-secretors, since no ABH antigen is produced. About 20% of Caucasians are non-secretors due to mutations of Nonsense G428A and C571T in FUT2 and therefore have strong but not absolute protection from norovirus GII.4. Non-secretors can still produce ABH antigens in erythrocytes, because the precursors are formed by FUT1. Some norovirus genotypes (GI.3) can infect non-secretors.
Epidemiological studies have shown that individuals with different ABH phenotypes are infected with strains of NoV by specific genotypes. GII.4 includes global epidemic strains and binds to more Histo-blood group antigens than other genogroups. A 2003 study in Japan revealed that children with type AB blood type (19.2%, 5/26) had a lower risk of infection than those with type A or O blood type. This study showed that individuals with AB blood is less susceptible to norovirus people, and type O is the most vulnerable.
History
The norovirus was originally named "Norwalk agents" after Norwalk, Ohio, in the United States, where an outbreak of acute gastroenteritis occurred among children at Bronson Elementary School in November 1968 (although the outbreak was discovered in 1936 in Roskilde, Denmark, at which is commonly known as "Roskilde syge" or "Roskilde disease"). In 1972, electron microscopy of stored human waste samples identified a virus, named "Norwalk virus". Many outbreaks with similar symptoms have been reported since then. The cloning and sequencing of the Norwalk virus genome indicates that the virus has a genomic organization consistent with the virus belonging to the Caliciviridae family. The name "norovirus" ( Norovirus for genus) was approved by the International Committee on Virus Taxonomy (ICTV) in 2002. But in 2011, press releases and newsletters were published by ICTV, which strongly encouraged the media, national health and scientific community to use the Norwalk virus virus name, rather than the genus Norovirus name, when referring to the plague. It is also a public response by ICTV at the request of an individual in Japan to rename the genus Norovirus because of the possibility of negative associations for people in Japan and elsewhere who have the surname "Noro". Before ICTV's position was published, ICTV consulted widely with members of the Caliciviridae Study Group and carefully discussed the case.
In addition to "Norwalk agent" and "Norwalk virus", the virus is also called "Norwalk-like virus", "small, round-structured viruses" (SRSVs), Spencer flu and "Snow Mountain virus". Common names of diseases caused by norovirus are still used including "Roskilde disease", "winter sickness disease", "winter vomiting bug", "viral gastroenteritis", and "nonbacterial acute gastroenteritis". This is also colloquially known as "stomach flu", but this is actually a broad name that refers to gastric inflammation caused by various viruses and bacteria.
See also
- Norovirus cis-acting replication element
References
External links
- NHS Health Options A-Z Norovirus Infection
- The global network and norovirus database
- CDC Viral Gastroenteritis FAQ: Centers for Disease Control and Prevention Factsheet Disease Factsheet
- "Norovirus in Healthcare Facilities Fact Sheet", CDC, released December 21, 2006
- tips from CDC for shipping travelers
- Reference Pathogen Virus and Resource Analysis (ViPR): Caliciviridae
- the Norovirus 3D macromolecular structure of EM Data Bank (EMDB)
- Viralzone: Norovirus
- ICTV
Source of the article : Wikipedia
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