What is ‘Shigella?’Shigella is a type of food poisoning which is similar to dysentery and tends to affect areas of the developing world such as South East Asia.

However it also occurs in industrialised nations.

It usually develops as a result of drinking contaminated water although it can be contracted by eating foods which have been in contact with infected water. One example of this is salads which are often washed in water before use.

Shigella can affect anyone but like any type of food poisoning, there are certain groups of people who are especially at risk. These include very young children and people who have a compromised immune system, e.g. AIDS sufferers.

This type of food poisoning is known as ‘Shigellosis’ or ‘bacillary dysentery’.

The shigella bacteria

This is a single cell, rod shaped bacterium which is also a known pathogen. This means that it is has the ability to cause disease or infection.

The shigella bacteria are very similar to the campylobacter, E coli and salmonella bacteria in that they all cause a form of food poisoning which is characterised by nausea, vomiting and diarrhoea.

There are 4 subspecies of the shigella bacteria which are:

  • Shigella flexneri
  • Shigella boydii
  • Shigella sonnei
  • Shigella dysenteriae

Flexneri, sonnei and dysenteriae are mainly responsible for outbreaks of shigella in developing countries. Shigella boydii is much less common.

Shigella sonnei accounts for more than 70% of cases in the West but a lesser number of these in the developing world. This type of bacteria appears to be more prevalent in industrialised nations.

Shigella flexneri accounts for around 60% of cases in the developing world.

Shigella dysenteriae tends to occur in areas of the developing world where there are large concentrations of people, for example, refugee camps.

Causes of shigella poisoning

This illness is caused by the consumption of infected food or more commonly, diseased water. It is contracted via the ingestion of contaminated food and/or water but also occurs from person to person contact.

It also occurs if someone who is infected handles or prepares food without proper attention to hygiene and food safety.

These bacteria are found within the waste products of infected individuals and can easily be transmitted to another person. This occurs if the infected individual does not wash their hands properly after visiting the bathroom and then makes contact with food or another, uninfected person.

It only takes a relatively small number of bacteria to cause shigella poisoning. These bacteria enter the digestive system where they attack the cells within the lining of the intestines. They release proteins into these cells which disrupt them and cause the lining to decompose.

This enables these bacteria to invade new cells and repeat the process.

After only a couple of days these bacteria will have destroyed these cells within the lining at the bottom of the large intestine and the rectum. This is often the cause of the bloody, mucus infected diarrhoea.

Symptoms of shigella poisoning

These include:

  • Nausea
  • Stomach upset
  • Vomiting
  • Severe diarrhoea which often contains blood and mucus
  • Fever
  • Rectal spasms

The incubation period –the time from the initial consumption to the appearance of these symptoms is usually 1 to 2 days. However, these symptoms can appear after as little as 12 hours.

Dehydration is a particular problem due to severe diarrhoea.

Diagnosing shigella poisoning

If you suspect that you have contracted shigella poisoning then contact your GP. He or she will examine you; ask you about the types of foods you have consumed recently and if you have been in contact with any water you suspect may be infected.

He or she will take a sample of your faeces –known as a ‘stool sample’which will be sent away to a laboratory for analysis. The results of this will confirm the diagnosis.

Treatment for shigella poisoning

Dehydration is the main problem here so it is important to replace any fluids lost as soon as possible. This means drinking plenty of fluids and including in these fluids, an ‘oral re-hydration’sachet. This sachet contains essential vitamins and minerals which will replace those lost due to vomiting and diarrhoea.

These sachets can be purchased at your local pharmacy or online.

If you have a severe case of poisoning then these fluids will need to be administered intravenously. This is done in hospital and is usually undertaken in high risk cases such as those involving young children or people with a weakened immune system.

This illness usually resolves itself within a set period of time but antibiotics can help to speed up this process. These are given in severe cases which may become potentially life threatening.

Anti-diarrhoeal medicines such as Immodium should be avoided as they can worsen the symptoms of this illness.

What is important to note is that even though this illness clears up after a week or so it often takes several months before your bowel motions return to normal.

Complications of shigella poisoning

These are likely to occur in people who fall into a high risk category, e.g. the elderly. They include severe dehydration, rectal bleeding and seizures.

A small percentage of people develop a condition called ‘Reactive Arthritis’. This is also known as ‘Reiter’s Syndrome’and causes painful swelling of the joints, pain during urination and sore eyes.

This occurs when the body’s immune system attacks its own cells whilst trying to fight off the shigella bacteria. It can last for several months and may result in chronic, long term arthritis.

Find out more about reactive arthritis in our complications of food poisoning section.

Prevention of shigella poisoning

This can be prevented by adopting the following measures:

  • Frequent washing of the hands by the infected individual and anyone who is in close contact with him/her.
  • If your child is infected then keep him/her away from uninfected children until he/she is fully recovered.
  • Anyone who is infected should not prepare or handle food until they are completely recovered.
  • Drink bottled water especially if you are travelling in areas of the developing world.

These are common sense measures which must be adhered to until all signs of the illness have disappeared.

Food Poisoning Guide

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