The giardia parasite or to be more precise – ‘giardia intestinalis’ - are types of organisms which cause an infection very similar to other forms of food poisoning.

Although the main difference here is that this is caused by drinking infected or untreated water rather than contaminated food. However, salads and vegetables which have been washed in infected water will also cause this illness.

The medical term for this disease is ‘giardiasis’.

This illness can occur in any part of the world which includes the UK but it is more commonly seen in developing countries. This is due to the fact that they have limited supplies of clean water and poor sanitation facilities.

Giardiasis is a particular problem for young children in those countries who are at greater risk of dehydration due to diarrhoea and other symptoms. Prolonged bouts of diarrhoea can lead to dehydration which can be fatal in babies and infants.

This illness is similar to cryptosporidium.

The giardia intestinalis parasite

This is a unicellular parasite which lives within the small intestine of people and animals. It does not invade cells within the lining of the intestinal walls or spread into the bloodstream as happens with other types of food poisoning; rather it remains attached to the intestinal wall.

Once there it reproduces asexually.

Causes of giardiasis

This occurs from any of the following:

  • Drinking water which is untreated or contaminated by infected faeces.
  • Eating foods such as fruit or vegetables which have been washed in contaminated water.
  • Failure to wash the hands properly after visiting the toilet followed by contact with food.
  • Anal sex

Parents and anyone who works in childcare, and who are required to change nappies are also at risk of this illness. If they change the nappy of a baby who has developed giardiasis then they too are at risk. They may come into contact with faeces which have been contaminated and then, unknowingly transmit this infection by touching other objects, food etc.

How is the giardia parasite transmitted?

This parasite lives within the small intestine. When faeces are expelled from the body this parasite is expelled along with them and is able to survive outside the body for a considerable period of time.

These parasites form hard protective shells and are known as ‘giardia cysts’.

They can survive for months in cold water which is why they often occur in mountain streams, ponds, rivers and lakes. This is a particular risk for campers and people who enjoy outdoor activities such as hiking or who swim in rivers and lakes where these bacteria can be found.

They are found in untreated water but even safe sources such as reservoirs can be risky as the giardia parasite can resist water treatment methods such as chlorination.

So, giardiasis is likely to occur in anyone who has come into contact with infected water, e.g. swimming in a lake, or has drunk any water which has been contaminated by infected faeces.

This is one of the reasons why people are advised to boil water when travelling or consume bottled water if necessary.

Symptoms of giardiasis

The incubation period for this illness is between 9 to 14 days or so after initial exposure.

Note: when we say ‘incubation period’ we refer to the period of time between first contact with the parasite and the appearance of the symptoms.

The symptoms include:

  • Fever
  • Loss of appetite
  • Nausea
  • Upset stomach
  • Watery diarrhoea

This diarrhoea is the main symptom of this illness and tends to be frequent and often foul smelling.

Other possible symptoms include belching (burping), bloated stomach and indigestion.

These symptoms usually ease after a couple of weeks but the diarrhoea can persist for much longer. In chronic cases, people suffer repeated bouts of diarrhoea for several years although this is rare.

Interestingly enough, the majority of people who become infected by the giardia parasite do not experience any symptoms at all. This is known as ‘asymptomatic giardiasis’.

However, these people can still transmit the infection to others.

Diagnosing giardiasis

This is done via a stool sample.

A stool sample is a test in which a small sample of faeces is analysed under a microscope to check for signs of the giardia parasite. Several samples may be required.

This test is often performed in other types of food poisoning.

Treatment for giardiasis

Giardiasis is treated with medication called metronidazole. This is available as a tablet and is a week long course of treatment.

Metronidazole works by killing the parasites which are responsible for giardiasis.

Side effects are rare but if you experience anything untoward such as nausea, skin rashes, blurred vision, dizziness or fits then consult your GP.

Complications of giardiasis

The main problem is that of dehydration. Giardiasis causes repeated bouts of diarrhoea which result in large amounts of fluids being lost. These fluids contain essential vitamins and minerals such as sodium which are vital for the functioning of the body.

This is especially dangerous for children as they are less able to tolerate this loss of fluids as compared to an adult. They have smaller bodies than adults which contain smaller amounts of fluids so any loss has a greater effect.

It is important to drink plenty of fluids such as water to prevent this from happening and to add an oral re-hydration powder. These powders are available from a pharmacy and contain replacement vitamins and minerals.

You just add this to a glass of water.

If your child has signs of dehydration then try this before seeking medical advice. But if their symptoms are severe then consult your GP.

Preventing giardiasis

Giardiasis can be prevented by adopting a few common sense measures which include good hygiene and food safety.

They include:

  • Avoid drinking untreated water. Buy bottled water when travelling. Boil your water if you are camping or camping.
  • Do not eat unwashed fruit and vegetables and especially if you are travelling abroad. Wash them first before consumption.
  • Wash your hands after you visit the toilet
  • Wash your hands before you prepare or cook food

These and other precautions are discussed further in our preventing food poisoning section.

If you or your child develops giardiasis then stay away from work/school for at least 48 hours or until the symptoms have eased. Use a separate set of towels, bedding, utensils from the rest of your family and always wash your hands each time you handle food.

Food Poisoning Guide

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