Giardia was, until recently, thought to be a harmless member of the gut flora, because it was sometimes found in the intestines of apparently healthy people. Only within the last few years have doctors begun to realize that this microbe can cause disease. It is found throughout the world, and about 5-15 per cent of people are infected. In Britain, these are usually people who have travelled abroad, especially to the tropics, which is where Giardia probably originated.

Giardia lives in the gut and produces microscopic hard-walled cysts that pass out of the body with the faeces. These can get into food or water, especially in countries with poor sanitary facilities, and thus infect other people. Giardia cysts are resistant to chlorine, at least in the amounts usually used for disinfecting water supplies.

For most people who become infested with Giardia there are no symptoms. Such people are infectious however, and if they are involved in food preparation and are careless about washing their hands, they may be the modern equivalent of ‘Typhoid Mary’, passing Giardia on to others.

Those who do suffer symptoms, when infected by Giardia, experience an acute attack of watery diarrhoea, with bloating, abdominal pain, belching and fatigue. This usually clears up of its own accord after a few days – thereafter the person has no symptoms but may remain infectious. However, some patients continue to suffer milder symptoms. Their main problem is that food is not absorbed from the gut properly. This produces loose, frequent stools, often foul-smelling and frothy. There may also be flatulence, pain, nausea, loss of appetite, weakness and weight loss. Children with this disease – and they are the most susceptible group – are often pale and stunted.

There may also be a milder form of the disease, in which there is no diarrhoea as such – discomfort, wind, belching and nausea are the main symptoms in these cases. Urticaria (nettle-rash), joint pains and feverishness may also be present. Not surprisingly, some of these patients are thought to have food intolerance. Indeed, many do, because Giardia, like Candida, seems to be linked in some way to food sensitivity.

Giardia infection can be diagnosed by looking for the parasite in the stools. It is treated by a short course of drugs, the main one used being metronidazole. This can have some side-effects, such as nausea and vomiting, but only has to be taken for about a week. Unfortunately, it seems to make candidiasis more likely, so anyone taking it would be well advised to adopt a sugar-free diet during the treatment, and for a month or so afterwards.


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