Norwalk virus
The species of human pathogenic noroviruses are non-enveloped, single-stranded RNA viruses of positive polarity belonging to the family Caliciviridae and the same genus Norovirus. Noro is an artificially formed prefix of Norwalk, which was 2004 official taxonomic designation. The highly contagious ( highly contagious ) Noroviruses cause in humans as well as other numerous viruses, the viral gastroenteritis ( viral diarrhea and vomiting, also colloquially referred to as gastro-intestinal flu). They are responsible for the majority of the non- bacterial induced diarrhea in humans, in addition to the rotavirus from the family Reoviridae. The detection of human noroviruses is especially notifiable disease in Germany according to § 7 of the Infection Protection Act.
First description
As the first human norovirus, the Norwalk virus was characterized in stool samples of a viral gastroenteritis outbreak of 1968 in Norwalk, Ohio by immune electron microscopy for the first time in 1972 morphologically. In order to prove the connection between the found virus and gastroenteritis disease, purified ultrafiltrate was chair ( isolated from human faeces of diseased patients) administered orally to volunteers, who subsequently also infected.
Morphology and classification
Noroviruses have a diameter 35-39 nm, and they have, in the electron microscope on a very fuzzy, round structure. They have an icosahedral (twenty -area ) capsid (T = 3 symmetry ), and an approximately 7.3 to 7.7 kb genome. Like most single-stranded RNA viruses are highly variable in their norovirus genome sequence, which is why a number of different subtypes and isolates are known. Show antigenic drift and antigenic shift a seasonal by genetic recombination between different Norovirusstämmen.
Currently three human pathogenic species norovirus, Norwalk virus, the species and the rarer species Human Norovirus Alphatron and Human Norovirus Saitama within the genus Norovirus are provisionally distinguished. The species Norwalk virus is currently divided into seven subtypes, with four of these subtypes can be again combined to very extensive genogroups 1-4 ( GGI to GGIV ). The isolates and subtypes are named according to an international scheme and classified:
- Subtype Desert Shield virus ( Hu/NV/DSV395/1990/SR )
- Lordsdale subtype virus ( Hu/NV/LD/1993/UK )
- Mexico subtype virus ( Hu/NV/MX/1989/MX )
- Subtype Norwalk virus ( Hu/NV/NV/1968/US )
- Subtype Snow Mountain virus ( Hu/NV/SMV/1976/US )
- Subtype Southampton virus ( Hu/NV/SHV/1991/UK )
Epidemiology
Noroviruses are spread throughout the world and have the typical non-enveloped viruses resistant to environmental influences on. They withstand temperature variations from -20 to 60 ° C and showed their " survivability " in a contaminated carpet even after twelve days. The man is considered to be the only reservoir host for human noroviruses.
Norovirus infection occur in Central Europe seasonal clustered in the months of November to March, but the activity in the summer months is only about ten times lower. The acquired through infection immunity against a viral strain lasts longer than until the next season, so the pathogen is exposed to a high selection pressure through herd immunity. This he dodges through genetic drift and shift.
Endemic Norovirus infection have so far (accumulating in geriatric wards ) demonstrated esp. in hospitals and old people's or nursing homes. In Switzerland, has estimated to be expected by these viruses annually 400000-600000 infections. In Germany 2007 198.992 cases or 1,370 clusters with five or more cases to the Robert Koch Institute were submitted for the reporting year. 75 % of outbreaks with indication of the environment played out in hospitals, retirement and nursing homes, 14% in kindergartens and nurseries. The increasing number of reported cases of infection of recent years are much also due to the improved and more frequent diagnosis. Until the 90s, the norovirus diagnosis was a few specialized laboratories reserved. Since commercially available immunoassays are available, a specific infection can frequently be detected by noroviruses.
In the fall of 2012, over eleven thousand people from East Germany have been infected from eating imported strawberries from China with the Norovirus.
Transmission
With a minimal infectious dose of only 10 to 100 virus particles, the contagiousness of norovirus is extremely high. Transmission occurs from person to person via a contact or smear infection. The viruses are excreted in the stool or vomit and orally transmitted by the faecal -oral route or by inhalation of the aerosol produced during vomiting. The infection with viruses can occur via contaminated objects. In addition, a recording of the pathogen via contaminated water is possible, this can lead to a food and drink, which were prepared with contaminated water, but also by drinking tap water, take place. Human noroviruses are compared to other viruses relatively environmentally stable and can survive several days to weeks in water at 25 ° C.
A direct zoonosis in the pig and cattle could also be shown.
Particularly at risk are the residents and the staff of community facilities of all kinds, because a local outbreak is promoted by using, for example, common toilets. In recent years, cruise ships were affected.
Usually the virus from diseased persons are excreted during the acute illness and up to 48 hours after resolution of clinical symptoms, but thereafter, the patients can be further 7 to 14 days symptomless virus shedders. There are also people who are far more than 14 days shedders and to show no symptoms, the virus can pass. Therefore, the careful attention to the usual hygiene rules even after the disease is of very great importance.
Symptoms and complaints
The incubation period of triggered by the human norovirus disease in humans is approximately 10-50 hours. Disease symptoms develop within a few hours to days and consist primarily of a gastroenteritis with suddenly occurring diarrhea and vomiting that can lead to significant fluid loss (see dehydration ). Therefore, especially children and the elderly are at risk. There is usually a distinct feeling of illness with abdominal pain, nausea, headache and muscle pain.
Consequences and complications
Depending on the severity of the condition of the water loss through the norovirus infection can also lead to death without treatment. The mortality rate is well below 0.1 %, affecting 70 to 80% of the elderly aged 80 years. Since 2001 in Germany reporting requirement for the disease. According to the Robert Koch Institute ( RKI), 12 people died in 2005 in the norovirus, 2006 16, 2007 76, 2008 67, 2009 30, 2010 56 and 2011 43
Proof
In the context of medical diagnosis, it is possible, but not always advisable to confirm norovirus in stool samples. The most commonly used, but also the most expensive method is the RT- PCR ( reverse transcription followed by proof of polymerase chain reaction). It has a high sensitivity and specificity. Other available methods of detection are the ELISA ( lower specificity ) and electron microscopy ( consuming). Of particular importance is the detection of pathogens in the context of outbreaks, as these special hygienic measures require. However, not every illness is examined for the organism, thus corresponds to the number of entries is not the true extent of the disease. Also, due to the lack of specific therapy, the need for an expensive stool diagnostics of professionals is doubted if already gastroenteritis were detected by noroviruses in the environment. A study on noroviruses in each patient is medically unnecessary and therefore very economical when disease cases are known in the area and the classical clinical symptoms are present.
A causative antiviral therapy is not known; the treatment is purely symptomatic and is only to compensate for the fluid and electrolyte loss (eg, sodium, magnesium, potassium, calcium, ... ). In severe vomiting, the use of nausea -reducing drugs ( anti-emetics ) may be considered. Especially in the elderly or small children may need a short hospital stay.
A preventive vaccine is not yet available. First experimental vaccines are under development.
Copper alloys with a copper content of at least 60 % show a toxic effect against noroviruses. Doorknobs, railings or handles such copper alloys in hospitals or nursing homes could therefore help to inhibit the spread of viruses in these environments.