Schistosomiasis is a vector borne helminth infection caused by the trematode flatworm. It is highly prevalent throughout the tropics. Infection is usually acquired through exposure to contaminated water, for instance, through bathing, swimming and washing clothes.
There are 3 major, geographically distinct, species responsible for human infection:
- S. mansoni – Africa, Middle East, Caribbean, South America
- S. haematobium – Africa, Middle East
- S. japonicum – China, SE Asia, Philippines
Several minor species that can cause human disease are also recognised:
- S. mekongi – Laos, Cambodia
- S. intercalatum and S. guineensis – Central and West Africa
Acute syndromes:
- Swimmer’s itch (cercarial dermatitis) is a self-limited itchy rash that presents 24 hours after exposure to contaminated water.
- Katayama fever is an acute hypersensitivity reaction to primary infection that occurs 3-12 weeks post exposure. It classically presents with low-grade fever, urticarial rash, abdominal pain and diarrhoea. Lymphadenopathy and hepatosplenomegaly may be present. Laboratory investigations often show an eosinophilia, however serology and stool/urine studies for eggs may be negative.
Chronic syndromes:
- Urinary (S. haematobium) – haematuria, dysuria, epididymitis. May result in scarring/calcification of the bladder and is a risk factor for SCC.
- Intestinal (S. mansoni, S.japonicum) – abdominal pain, diarrhoea, faecal occult bleeding, ulceration and pseudopolyp formation. May mimic inflammatory bowel disease or colorectal cancer.
- Hepatic (S. mansoni, S. japonicum, S. mekongi) – hepatomegaly, pre-portal fibrosis, risk hepatocellular carcinoma.
C.M & N.B 12-12-23
Who to refer:
All those with:
- positive schistosomal serology
- unexplained eosinophilia where parasitic infection is suspected, and advice or review is required
- suspected Katayama fever who may have negative Schistosoma-specific investigations in the early stage for advice and followup.
Patients with fever returning from a malaria endemic region should be discussed with the on-call Infectious Diseases registrar/consultant via the WGH switchboard (0131 537 1000).
How to refer:
To Infectious Diseases at the Western General Hospital via Sci Gateway.
Swimmer’s itch is managed supportively e.g. with antihistamines.
Patients with a history of freshwater exposure in an endemic area (e.g. Lake Malawi) should be screened with serology (5-10mLs clotted blood/serum). This can be ordered via the search button on the GPOC / ICE index: please ensure that symptoms, travel history and date of suspected exposure are documented. Routine bloods (FBC, C&Es, LFTs) are useful.
Please note that serology takes at least 8 weeks to become positive after exposure; please do not send samples before this stage.
If there is concern about schistosomal infection earlier than 8 weeks post exposure e.g. Katayama fever, then patients should be discussed with the Infectious Diseases registrar/consultant on-call via switchboard.
All febrile returning travellers should be risk assessed for the possibility of malaria or high consequence infectious disease.
