Virus foodborne disease

Viruses are frequent causes of foodborne disease in the US and other countries. Food borne viruses infect through ingestion and are passed through the feces.

Any virus that is excreted in feces in sufficiently large numbers and manages to survive outside the body of the host long enough to contaminate food has the potential to spread through this route.

Viruses differ from bacteria in that they are smaller, require a living animal or human host to grow and reproduce, do not multiply in foods and are nor complete cells.

Viruses involved in foodborne disease outbreaks include, but are not limited to norovirus, hepatitis A virus, human rotavirus, hepatitis virus, astrovirus, sapovirus, aichi virus and adenovirus, as well as human enteroviruses such as echoviruses, polioviruses, group A and B coxsachieviruses.

The great majority of these are RNA viruses, often small and containing single-stranded RNA. They infect via the intestinal lining, but some are transported to the over (and occasionally other organs) before causing disease.

Norwalk and Norwalk-like viruses are the leading reported cause of foodborne viral illness. A member of the Calicivirus family of viruses, Norwalk virus particles are 27 to 38 nm in diameter and consist of a single positive strain of RNA.

Norwalk virus was first discovered following an outbreak of epidemic gastroenteritis in a Norwalk, Ohio, elementary school in 1968.

Outbreaks of ‘food poisoning’ or foodborne gastroenteritis over the years have been assumed to be caused by bacteria, whether or not such organisms are identified.

Washing hands and cooking foods are probably the two measures that contribute the most to preventing foodborne viral disease.
Virus foodborne disease

Calicivirus or Norwalk-like Virus

Calicivirus or Norwalk-like Virus
Diagnosis

• Diarrhea occurring in an outbreak especially in a closed environment
• Tends to infect older children and adults rather than infants
• Nausea and vomiting are common; bloody stools are rare
• Incubation period 1 – 2 days; illness: 1- 4 days
  

Epidemiology
Even in developed countries, antibodies to calicivirus are nearly universal by age 5. Infections tend to occur in family or community outbreaks. In undeveloped countries, infection by these viruses occurs presumably as a result of poor sanitation. In developed countries, outbreaks that occur year round have been describe in school, resorts, hospital , nursing homes, restaurants and cruise ships.

The primary method of spread is fecal-oral but contaminated water or shell fish has accounted for common source of outbreak. A measure of the importance of these agents is that – 10% of all gastroenteritis outbreaks and up to 90 – 95% of those that are non-bacterial are attributed to them. In contrast to infants, who are more often infected by rotavirus, calicivirus cause disease primarily in older children and adults. Immunity is probably short lived at best, suggesting that humoral antibody is not adequately protective. The incubation period is 1 – 2 days, and shedding can persist for 1- 2 weeks.

The Norwalk agent and related viruses are classified as caliciviruses, although they are also similar in appearance to parvoviruses and hepatitis A virus. Among the other human enteric caliciviruses which are named for where these strains were first detected. The human enteric calicivirus are now divided into two genera, provisionally named “Norwalk like virus” and “Sapporo like virus”.

Symptoms
Although calicilike viruses are typically associated with diarrheal illness, nausea and vomiting may occur frequently, especially in children. Bloody stools do not occur. Fever may be present in up to one third of patients. The incubations period in 24 – 48 hrs and the illness lasts 1 – 4 days.
Calicivirus or Norwalk-like Virus