Atlas of foodborne infections
transmitted by contaminated food and water

Atlas of Patogens Contents Information sources Glossary Administration

Norwalk Virus

CZ:
EN: Norwalk Virus

Occurrence:
Fish and Fish Products
Water and Beverages
Delicatessen
Cereals


Category:
Viruses


Foodborne Disease:
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Food-borne viruses are generally enteric, being transmitted by the fecal-oral route. However, transmission by person-to-person contact and via contaminated water is common, as with other enteric viruses. Hepatitis A and NLV are more commonly transmitted via foods than other food-borne viruses. The most important food-borne viruses are: hepatitis A, NLV, astrovirus and rotavirus.

acute gastroenteritis - nausea, vomiting, diarrhea and abdominal cramps


Description:
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Norwalk virus is the prototype of a family of unclassified small round structured viruses, which may be related to the caliciviruses. Norwalk and Norwalk like viruses also are referred to as “noroviruses”. Common names of the illness caused by the Norwalk and Norwalk-like viruses are viral gastroenteritis, acute nonbacterial gastroenteritis, food poisoning, and food infection. Norwalk and Norwalk-like viruses have been associated with outbreaks in communities. Foods such as raw oysters, cake frosting and salads, as well as drinking water, have been implicated as a common source of viral infection in several outbreaks.

Infection symptoms include nausea, vomiting, diarrhea and abdominal cramps. The incubation period is between 12 and 48 hours (average of 36 hours, with usual duration of 12-60 hours). Symptoms experienced less often include headache, fever, chills and myalgias. Fluid replacement is the common therapy.

Transmission of Norwalk virus is through the fecal-oral cycle. Although food is an efficient means of transmitting these agents, Norwalk and Norwalk-like viruses can be transmitted via water and by person-to-person contact. Transmission is of special concern for the fishing industry, since molluscan shellfish, being filter feeders, are readily contaminated with the stool-shed viruses present in human sewage. The virus has been identified in clams and oysters by radioimmunoassay.

Norwalk virus was the first gastroenteritis virus reported to be food borne. This group of viruses has recently been classified as members of the calicivirus family. The term "small round structured viruses" (SRSV) was originally applied to these agents owing to their appearance under the electron microscope. NLV are difficult to detect, especially from foods.
Exposure is by contact with infected individuals or fecally contaminated water or other materials.

Shellfish (bivalve molluscs) have been the predominant food vehicle. Shellfish beds may frequently become contaminated with human feces from sewage discharge. Aerosolization of vomitus-containing virus particles.


Pictures:

Norovirus particles in faeces
Source: Norovirus particles in faeces

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