What are enteric viruses?
Enteric viruses are viruses that enter via the intestinal tract and are usually spread by contaminated food, water, or indirect contact with contaminated faeces. There are two types of enteric viruses:
- True gut inhabitant viruses: These viruses replicate in the enteric tract and cause specific gastrointestinal symptoms such as diarrhoea and vomiting.
- Viruses that spread to other parts of the body: Viruses that are capable of spreading to other parts of the body include poliovirus that destroys motor neurons that causes paralysis and Hepatitis A and E viruses that cause liver disease.
Aetiology
Viruses are responsible for the majority of infective diarrhoeas, and viral gastroenteritis is the second most common viral illness after upper respiratory tract infections. Viral gastroenteritis is the number one killer of undernourished infants. Rotaviral infections alone are responsible for 500,000 deaths per year.
Types of viruses found within the gastrointestinal tract
- Rotavirus
- Caliciviruses e.g. Norovirus
- Adenoviruses 40 and 41
- Astrovirus
This article will look at Rotaviruses and Noroviruses in detail.
1. Rotavirus
Rotavirus is a member of the Reoviridae family and was first found in humans in 1973. Rotavirus accounts for up to 80% of all cases of viral gastroenteritis and occurs at an average of 60 days of diarrhoea per year in developing countries, causing major nutritional deficiencies and stunted growth in children. There is a 30% mortality rate in malnourished children, responsible for half a million deaths a year. Rotavirus causes the highest level of diarrhoea worldwide.
The virus replicates in intestinal epithelial cells, leading to a reduced capacity to absorb water, glucose and salt. This causes problems in secreting intestinal fluid and subsequently the acute onset of vomiting and watery diarrhoea.
Signs and symptoms
Symptoms usually begin within 2 days of infection and can include:
- Abdominal cramps
- Vomiting
- Extremely watery stool diarrhoea
- Low fever
- Large amounts of stool output
The most common sign is dehydration, but other findings can also include:
- Sunken eyes
- Hyperactive bowel sounds
- Fast heartbeat over 100 beats per minute (Tachycardia)
- Diarrhoea-induced dermatitis
- Weight loss
Laboratory Studies
Rotavirus can be detected mostly through a laboratory-conducted enzyme immunoassay, latex agglutination assay and electron microscopy.
Management
A rotavirus infection lasts for three to seven days and medication is usually not required. Oral rehydration therapy is administered to prevent dehydration. In severe cases, intravenous fluids are given to counter the loss of essential nutrients.
Prevention
Rotavirus can be prevented via vaccination immunisation and good hand hygiene to stop transmission of the virus and to prevent risks of ingesting the virus.
2. Norovirus
Norovirus is a highly contagious virus that causes acute gastroenteritis – vomiting and diarrhoea – and is responsible for up to 10 % of serious gastroenteritis cases. The source of this virus is contaminated seafood such as oysters and shellfish, as well as water.
Aetiology
Norovirus is a major cause of food-borne outbreaks of gastroenteritis and affects more than 260 million people per year. Death is usually seen in young children under the age of 5, the elderly and those who are immunocompromised.
Transmission
Large amounts of virus particles are shed through tiny drops of vomit and faecal matter that accidentally ends up in food. Food grown in contaminated water, such as watercress and shellfish, also have high chances of transmitting the virus through contaminated food products.
A small infective dose of less than 10 viral particles is enough to cause serious infection, severe diarrhoea and vomiting.
Signs and symptoms
Symptoms develop between 24 to 48 hours after ingestion of contaminated food products or water. These symptoms include:
- Non-stop vomiting
- Nausea
- Abdominal pain and cramps
- Feelings of discomfort that are difficult to classify (Malaise)
- Body ache (Myalgia)
- Fever
- Tachycardia
Diagnosis
Detection of norovirus can be examined via these studies:
- Immune electron microscopy – a special immune serum media is used to detect the virus in stool samples
- Nucleic acid amplification tests – the most accurate test due to high sensitivity and specificity for virus
- Serum Antibody titres – antibodies (Immunoglobulin M and immunoglobulin G) can be detected in a period of 14 days after initial infection
Management
With large amounts of fluids passed through the stools and vomiting, oral fluids and electrolyte replacements are essential to ensure that the body is not dehydrated and compensates for nutrients being lost.
Antiemetic medications are prescribed to relieve nausea and committing.
Prevention
- Frequent washing of hands, especially before a meal
- Avoid preparing food for others if you have recently been infected, at least for two weeks after symptoms stop.
- Cook seafood and freshwater vegetables thoroughly
- Children, especially, should avoid touching contaminated surfaces as they are more prone to putting their hands in their mouths
- Washing clothing that has been soiled by vomit or faeces
Conclusion
Enteric viruses are primarily transmitted through the faecal-oral route via the ingestion of contaminated food or water and contact with an infected person. It is essential to practice good hygiene and ensure that the food we eat come from clean sources and have been cooked thoroughly, to prevent possible infection.
