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Q A patient swam in Lake Malawi two weeks ago and came in asking for treatment 'just in case' of schistosomiasis How soon after infection will tests be positive and which is best?

A Exposure in Lake Malawi is an increasingly common source of schistosomal infection and both

S. haematobium and

S. mansoni are endemic, so infection may be with either the urinary or intestinal forms. Like most other helminths, schistosomes cannot reproduce in the human host, so disease presentation depends on infecting dose.

The majority of travellers with infection will be asymptomatic, the most commonly reported symptom being tiredness. A small proportion present with a febrile hypersensitivity reaction to schistosome larval migration called Katayama syndrome, but serological testing and stool and urine sampling will be negative in this phase of the illness.

Given the non-specific nature of early infection in travellers and the possibility of long-term complications, blind treatment is not recommended. Worms take six to 10 weeks to start egg production, so screening should be delayed until about 12 weeks after last exposure.

Serological testing (ELISA for egg antigens) is positive in about 85 per cent of UK cases and ova are detected on microscopy of clinical specimens in about 45 per cent. About 45 per cent will show a peripheral blood eosinophilia and urine dipstick for blood and protein may be positive. None of the tests is sufficient individually to rule out infection. Microscopy of stool will detect S. mansoni eggs and of terminal urine samples, S. haematobium.

Praziquantel is used for treatment of schistosomiasis but there is a 1-2 per cent failure rate and it is recommended that patients are referred to specialist infection departments.

Dr William Newsholme, specialist registrar in tropical and infectious diseases, Hospital for Tropical Diseases, London

Related Seminar: Musculoskeletal Medicine

Clinical Seminar: Musculoskeletal Medicine

What: A one day refresher to update GPs on the hot issues and trickiest dilemmas in rheumatology and orthopaedics.

When: Thursday 5 November 2009

Where: Raddison Hotel, Manchester

Next steps: Find out more and book

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