Norovirus is the group of RNA-containing viruses that belong to the Caliciviridae family. Norwalk virus is the only species of the genus Norovirus. Serotypes, strains and isolates include Norwalk virus; Hawaii virus; Snow Mountain virus; Mexico virus; Desert Shield virus; Southampton virus; Lordsdale virus and Wilkinson virus. The RNA genome in noroviruses easily mutates to produce new norovirus types.
Viruses in Norovirus are non-enveloped, with icosahedral geometries.
Noroviruses are the common cause of gastroenteritis (90% of cases).
The virus is transmitted:
- by fecally contaminated food or water;
- by person-to-person contact (in 62-84% of cases) via aerosolization of vomited virus and subsequent contamination of surfaces.
Norovirus is highly contagious. It was estimated that 20 viral particles are enough to cause the disease. An affected person continues to shed viruses and remains contagious even up to several weeks after the symptoms had vanished.
Norovirus infection usually affecte people in winter, although it may be caught in every season.
According to the U.S. Department of Health and Human Services the most common causes of human norovirus infections are:
- contaminated foods;
- ready-to-eat foods that were handled by infected workers (salads, ice, cookies, fruit, sandwiches etc.);
- any food contaminated with the feces or vomit of an infected person;
Potable water and lake or swimming pool water (when ingested) may also be the source of the infection.
When the virus gets into the body it starts to replicate within the small intestine. 12-48 hours after the exposure occur the first symptoms of the disease. The disease is associated with the damage to the microvilli in the intestine and increased epithelial cells apoptosis. D-xylose and fat malabsorption induce diarrhea. Vomiting is caused by the changes of the gastric motility.
People whose immune system are weakened (for example by AIDS, immunosuppressive therapy) are more likely to get infected. Children are at risk as well as they are visiting childcare centers and usually don’t
follow hygiene procedures. Staying in hotels, cruise ships, vacation resorts where there are lots of people together increases the risk of infection. If the person is not following the food hygiene he/she is at risk of infection.
Symptoms of norovirus infection include:
- nausea – usually the first symptom;
- vomiting – sometimes violent and sudden (more common for children);
- stomachache (abdominal pain);
- abdominal pain or cramps;
- watery or loose nonbloody diarrhea;
- suddenly feeling unwell and lethargic (malaise);
- fever and chills, usually mild;
- myalgias (body aches);
- loss of taste and appetite;
- tachycardia (fast heart rate);
- arterial hypotension;
- the absence of tenderness of the abdominal wall;
Vomiting and diarrhea lead to the loss of the fluids and electrolytes. Symptoms of dehydration include dizziness when standing (due to arterial hypotension), dry mouth, and decreased urination.
The disease usually lasts 2-3 days and resolves without any treatment. Severe illness is not common.
Rarely Norovirus may result in malnutrition, constipation, dyspepsia and reflux.
To determine the cause of gastroenteritis, polymerase chain reaction (PCR) is performed. ELISA is made to estimate the level of antibodies, although this test is neither enough sensitive nor specific.
Noroviruses may be detected in the stool with the help of enzyme-based immunoassays (EIA).
See also Norovirus test.
There is no specific treatment for the norovirus infection. Vomiting and diarrhea cause dehydration and requires oral (Infalyte, Kao Lectrolyte, Naturalyte, Oralyte), and sometimes intravenous fluids along with the electrolyte replacement (Pedialyte or Gatorade).
Antiemetics (promethazine) are used for nausea and vomiting and analgesics (ibuprofen, acetaminophen) to relieve for myalgias and headache. Severe diarrhea is an indication for antiperistaltic agents.
Affected individuals are recommended to follow some dietary restrictions during the course of the disease, they should eat soups; starches and cereals, such as potatoes, noodles, rice or crackers; banana; yogurt and broiled vegetables.