Food poisoning factsheets - Giardia infection

What is Giardiasis and how is it caught?

Giardiasis is the term for an infection with a microscopic single celled animal called Giardia lamblia. You can be infected without knowing it but it can be a long term diarrhoeal illness. Complications are rare and it’s readily treated once recognised.

The main source of the organism is the human intestine and, less commonly, animal intestines. Affected animals and humans may be entirely well.

Giardiasis is easily caught because only a small number of organisms are needed to cause infection. It can be spread directly, for example the hands coming into contact with infected faeces and then touching the mouth, or indirectly whereby a person or animal contaminates a water source and another drinks from that water.

The time between getting the infection and becoming ill is usually between 5 and 25 days; most commonly 7 to 10 days. Giardia can form cysts which survive for a long time. These cysts are more likely to be passed out by people who have been infected for some time but had no symptoms. Someone who is unwell because of Giardia lamblia will be excreting the fragile form of the organism, which will survive less well in the environment. Those that are ‘well’ with Giardia can pose a higher risk of infection than those that are unwell.

What are the symptoms of Giardiasis?

Most people with Giardia remain well. Those that are unwell have abdominal cramps and diarrhoea and may find their uptake of fats is affected, resulting in greasy, pale faeces.

How do you know if you have Giardiasis?

Many different kinds of illness can cause diarrhoea and abdominal cramps so Giardiasis can only be diagnosed by examining a stool sample in a laboratory. If Giardiasis is discovered in someone with no symptoms, then no treatment will be needed.

How is Giardiasis treated?

A short course of antibiotics cures the condition and once treated, it can no longer be passed on. Occasionally problems can arise with the pancreas and bile system.

What can I do to prevent Giardiasis and what can I do if I have it?

There is no vaccine nor do you become immune to it. The best way to avoid infection is by strict hygiene, particularly after dealing with babies and children with diarrhoea and after handling animals. Giardia is resistant to disinfectants such as ammonia and chlorine.

Occasionally, contaminated water is the source of infection and the only way to make it fit to drink is to bring it to the boil as this kills Giardia instantly.