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Schistosomiasis in travellers returning from sub-Saharan Africa

^a Hospital for Tropical Diseases, London NW1 0PE

Correspondence to: Dr Wright.

Cases of schistosomiasis seen at this hospital have increased in the past five years (fig 1). Many of these patients were travellers whose only fresh water exposure was in Lake Malawi. We therefore reviewed all cases of proven schistosomiasis diagnosed at this hospital between 1991 and 1994.

View larger version (19K): [in this window] [in a new window]   Fig 1--Schistosoma haematobium and S mansoni infection in travellers attending the Hospital for Tropical Diseases, London, 1967-94

Methods

and results

We used parasitology records to identify patients with proved schistosomiasis (in whom schistosome ova were identified) attending this hospital between 1 January 1991 and 31 December 1994. Patients with an enzyme linked immunosorbent assay (ELISA) positive for schistosomes in whom ova were not found were excluded. Patients' characteristics, travel history, and laboratory data were recorded; cases in "travellers" were distinguished from "indigenous" cases.

A total of 344 cases of schistosomiasis was identified; 222 (65%) cases were in men. Median age was 25 (range 3-65) years; 238 (69%) cases were in travellers and 106 (31%) in "indigenous" patients.

Schistosoma haematobium was identified in 221 cases (64%), S mansoni in 117 (34%), and S intercalatum in six (2%). One patient had mixed infection with S haematobium and S mansoni; in another case it was impossible to speciate the ova. All but one of these patients had been in Africa or the Middle East.

S haematobium ova were isolated from urine (191 patients), rectal snips (20), stool (14), semen (13), bladder biopsy (6), vulval biopsy (3), cervical smears (3), and cervical tissue after hysterectomy (1). S mansoni was isolated from stool (67 patients), rectal snips (49), urine (1), and bladder biopsy (1). Ova were occasionally identified in more than one site in the same indi-vidual. An eosinophil count was performed in 316 of the 344 cases. Eosinophilia (>/=0.4 x 10⁹/l) was present in 205 patients (65%). Schistosome ELISA was performed in 318 of the 344 cases; positive results were found in 258 (75%).

Among travellers, 77 (32.4%) gave Lake Malawi as their only fresh water exposure in an endemic area. Of these, 76 were infected with S haematobium and one with S intercalatum.

Comment

The increase in the number of travellers infected with S haematobium may reflect an increase in travel to Malawi; more than twice as many British residents visited Malawi in 1993 as in 1987 (R Behrens, personal communication). Until recently, Lake Malawi was believed to be the only lake in the Rift Valley free from schistosomiasis.¹

Patients with S haematobium present with haematuria, dysuria, or urinary frequency, whereas abdominal pain, diarrhoea, or rectal bleeding are associated with S mansoni. Most of our patients had light infections, causing minor symptoms or none at all.² Serious complications such as neurological deficit can arise,³ so it is important that those at risk are identified by a detailed travel history and offered appropriate screening tests.

This hospital offers screening to any patient who has been exposed to fresh water in an area endemic for schistosomiasis, regardless of whether they have symptoms. This involves microscopy of stool (after formol ether concentration) and terminal urine (the last few drops of urine produced during micturition); eosinophil count; and schistosome ELISA. Snips of rectal mucosa may be examined when ova are not detected in urine or stool specimens and serology is positive for schistosomes or when the patient has unexplained eosinophilia. Screening should start a minimum of six but ideally 12 weeks after exposure, as schistosome ova begin to be laid 25-31 days after infection.⁴

We thank the staff of the parasitology department for their advice and assistance.

Funding: None.

Conflict of interest: None.

1. Whitworth JAG. Schistosomiasis. BMJ 1993;307:936. [Free Full Text]
2. Harries AD, Walker J, Fryatt R, Chiodini PL, Bryceson ADM. Schistosomiasis in expatriates returning to Britain from the tropics: a controlled study. Lancet 1986;i;86-8.
3. Blanchard TJ, Milne LM, Pollock R, Cook GC. Early chemotherapy of imported neuroschistosomiasis. Lancet 1993;341:959.
4. Jordan P, Webbe G, Sturrock RF, eds. Human schistosomiasis. London: CAB, 1993:16.

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