Organism The small flagellate Giardia intes-tinalis (lamblia) is a common commensal of the human small intestine, but heavy infections can cause diarrhoea.

Clinical features Faeces are loose and greasy with an unpleasant odour. Bloating and abdominal distension can occur. Chronic infections can produce partial villous atrophy with a resulting malabsorption syndrome. Giardia is one of the causes of traveller's diarrhoea.

Diagnosis The characteristic 'face'-shaped flagellate is occasionally seen in the faeces, easily detected by its high motility, but the cysts are more commonly found (Fig. 9.1). Jejunal biopsy or the duodenal string test may be performed in the differential diagnosis of the malabsorption syndrome.

Transmission is by person-to-person transfer of cysts from the faeces of an infected individual or by contamination of food or water. Infected food handlers are often responsible for infecting people in restaurants, while a poorly maintained water supply disseminates infection more widely. The cysts can survive for several weeks in fresh water and are not killed by normal levels of chlorine. An animal reservoir might also be responsible.

Incubation period 3-25 days; mean 710 days.

Period ofcommunicability The organism can persist in the bowel for many months and during all of this time the infection can be transmitted.

Occurrence and distribution The infection is found worldwide, but is more common in the tropics and where conditions of hygiene are poor, ensnaring the unsuspecting traveller with chronic diarrhoea. Heavy infections occur in children, especially those in institutions or debilitated by other conditions.

Control and prevention Individuals who are rigorous with their personal hygiene can largely avoid infection. Drinking water can be boiled or treated with five to ten drops of iodine per litre of water. Proper food handling and preparation, especially the washing of hands is essential, while long-term prevention is through proper sewage disposal and the protection of water supplies.

Treatment is with tinidazole either as a single dose of 2 g or 300 mg a day for 7 days. Metronidazole can also be used.

Surveillance Giardia is a common infection in travellers and a routine stool examination after travelling to a less-developed area is advisable.

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