Viruses

Summary

Norovirus is a highly infective human virus that can be passed from person-to-person or by contaminated food. Food vehicles for it include foods contaminated by an infected handler, contaminated during irrigation or washing and sewage-contaminated bivalve shellfish. These filter feeders can accumulate viruses if the waters they inhabit are polluted with human sewage. They can also be a source of hepatitis A and E. Hepatitis E has also been found in meat from pigs, wild boar and deer. 

Norovirus, sometimes called the ‘winter vomiting bug’, is a common cause of gastroenteritis (stomach flu) affecting 600,000-1 million in the UK every year. It is a highly contagious virus that can infect anyone. You can get it from an infected person, contaminated food or water, or by touching contaminated surfaces. Globally, the virus affects around 267 million people and causes over 200,000 deaths each year – usually in less developed countries in the very young, elderly and immunosuppressed (Debbink et al,. 2012). Outbreaks often occur in closed communities such as hospitals, schools and cruise ships, where infection spreads rapidly by person-to-person transmission or through contaminated food. Norovirus is shed in huge quantities in the faeces and vomit of infected people and as few as ten viral particles can cause infection (Matthews et al., 2012).

Norovirus outbreaks can also occur from bivalve shellfish such as oysters, infected by sewerage-contaminated water. Bivalve shellfish are commonly involved in outbreaks of foodborne viral diseases and can carry norovirus as well as other viruses (hepatitis A and E). Oysters and mussels are filter feeders and if the waters they inhabit are polluted with human sewage, they can accumulate viruses. This gives another meaning to the term ‘bottom-feeder’! Other sources include foods contaminated during irrigation or washing and foods contaminated by an infected handler. Most people who are infected can look after themselves at home; antibiotics don’t help because the infection is caused by a virus. Some evidence suggests the presence of noroviruses in pigs and cattle, but there is no evidence yet for direct transmission to humans.

Other foodborne viruses (such as hepatitis E) have been found in meat from pigs, wild boar and deer (EFSA, 2011). Although foodborne transmission of hepatitis E may be relatively rare, the virus can be transmitted through consumption of undercooked meat. Several studies suggest the following food items as risk factors for infection: pork pies, liver pâté, wild boar, under-cooked or raw pork and sausages (EFSA, 2011). The European Food Safety Authority say that high risk groups (people with underlying liver disease, immuno-compromised people and pregnant women) should be discouraged from eating meat and liver derived from wild boars and domestic pigs without proper cooking for prevention of hepatitis E (EFSA, 2011).