Schistosomiasis

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Schistosomiasis is caused by blood flukes whose lifecycle requires freshwater snails. Free-swimming cercariae penetrate exposed skin, mature through hepatic migration and pair within venous plexuses. Adult worms can persist for years. Disease is driven mainly by immune granulomas and fibrosis around eggs retained in tissues rather than by the adult worms themselves.

Species predicts anatomy. S. haematobium adults inhabit pelvic venous plexuses and eggs traverse the urinary or genital tract. S. mansoni and S. japonicum primarily affect bowel and portal circulation; japonicum produces many smaller eggs and can disseminate more widely. Travel geography, timing and clinical phenotype guide which samples to collect.

Low-intensity infection is often asymptomatic but still deserves assessment because chronic injury is preventable. Eosinophilia supports helminth infection but is neither universal nor specific. Serology is particularly useful in travellers, whereas microscopy demonstrates active egg excretion and allows species recognition but lacks sensitivity after light exposure.

Screening and management of eosinophilia across all helminths follows the BIA returning-traveller pathway. The focus here is schistosome exposure, organ pattern, diagnostic timing, praziquantel use and surveillance of urinary, intestinal, hepatic and neurological consequences.

Key points

Schistosome cercariae penetrate intact skin during contact with contaminated freshwater containing infected snails; properly chlorinated pools and seawater do not transmit infection.
An itchy cercarial rash can occur within days, while Katayama fever with urticaria, cough, diarrhoea and eosinophilia usually appears weeks later during early egg production.
S. haematobium causes urogenital disease with terminal haematuria, bladder and ureteric fibrosis and squamous-cell bladder-cancer risk; S. mansoni and S. japonicum cause intestinal and hepatosplenic disease.
First-line assessment combines a precise freshwater history, FBC with eosinophils, schistosome serology and targeted urine or stool microscopy after sufficient time for maturation.
Definitive parasitological evidence is characteristic eggs in urine, stool or tissue, but low-burden traveller infection often requires serology and repeated concentrated specimens.
Collect S. haematobium urine near midday, ideally terminal urine after activity; collect multiple stool samples for intestinal species because egg excretion varies.
Praziquantel is the treatment of choice for mature worms: commonly 40 mg/kg orally in two divided doses during one day for S. haematobium or S. mansoni.
For S. japonicum or S. mekongi, specialists may use a 60 mg/kg total oral dose in two or three divided doses over one day; species and local protocol must be confirmed.
Praziquantel has limited activity against immature worms, so very early treatment can fail and repeat therapy after maturation may be required.
Prevention is avoidance of untreated freshwater in endemic areas; there is no licensed vaccine or dependable pre-exposure tablet for travellers.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Freshwater cercariae

Larvae released from infected aquatic snails penetrate intact human skin during swimming, washing, wading or occupational water contact.

Urogenital species

S. haematobium adults reside mainly in pelvic venous plexuses and release eggs toward bladder and genital tissues.

Intestinal species

S. mansoni, S. japonicum and related species occupy mesenteric veins, directing eggs through bowel or into portal circulation.

Sustained transmission cycle

Human urine or faeces contaminates freshwater with eggs, miracidia infect suitable snails, and amplified cercariae emerge to infect another person.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Skin penetration
Cercariae shed their tails, cross skin and become schistosomula, sometimes provoking a local itchy immune reaction.
2
Systemic maturation
Larvae migrate through lungs and liver before adult pairing; early egg production can trigger immune-complex Katayama fever.
3
Egg granulomas
Egg antigens provoke eosinophil-rich granulomatous inflammation that helps tissue passage but also injures bladder, bowel and ectopic sites.
4
Progressive fibrosis
Repeated egg deposition and healing produce ureteric obstruction, calcified bladder, genital scarring or periportal Symmers pipe-stem fibrosis.
5
Ectopic deposition
Venous shunts or aberrant migration carry eggs to spinal cord, brain or lungs, where confined inflammation causes disproportionate damage.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Cercarial dermatitis

An itchy papular eruption or prickling develops at freshwater-exposed skin within hours or days and usually settles without proving established infection.

Katayama syndromeRed flag

Fever, chills, urticaria, cough, myalgia, abdominal pain or diarrhoea with eosinophilia several weeks after first heavy exposure reflects systemic immune-complex disease.

Urinary disease

Terminal haematuria, dysuria, frequency, pelvic discomfort or calcification suggests S. haematobium egg deposition in bladder and distal ureters.

Genital schistosomiasis

Vaginal bleeding, discharge, dyspareunia, infertility, seminal symptoms or genital lesions can arise from chronic pelvic egg inflammation.

Intestinal disease

Intermittent abdominal pain, diarrhoea, blood in stool, polyps or protein loss can accompany mansoni or japonicum egg passage through bowel.

Hepatosplenic diseaseRed flag

Firm hepatosplenomegaly, thrombocytopenia, varices or ascites indicates periportal fibrosis and portal hypertension, often with relatively preserved synthetic function.

NeuroschistosomiasisRed flag

Myelopathy, radicular pain, cauda-equina symptoms, seizure or focal cerebral signs arise when eggs lodge in spinal or cerebral tissue.

Red flags requiring action

Acute weakness, saddle sensory change, urinary retention or incontinence after endemic freshwater contact requires emergency spinal imaging and specialist treatment.
Seizure, focal neurological deficit, severe headache or altered consciousness may represent cerebral schistosomiasis and needs urgent neuroimaging.
Fever, urticaria, cough, diarrhoea and marked eosinophilia several weeks after a heavy first exposure suggests acute Katayama syndrome, which can worsen around treatment.
Haematemesis, melaena, splenomegaly or thrombocytopenia can indicate portal hypertension from chronic hepatosplenic disease despite preserved hepatocyte function.
Visible haematuria, obstructive uropathy, hydronephrosis or a bladder lesion requires urological evaluation because chronic urinary schistosomiasis causes fibrosis and cancer risk.
A negative early serology or single urine or stool microscopy does not exclude infection; testing sensitivity depends on timing, burden, species and specimen collection.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
First-line exposure and eosinophil assessmentFirst stepFirst line
Why
Establish whether schistosomiasis is plausible and identify systemic or organ injury.
Interpretation and limitations
Record exact water body, country and date, then request FBC with differential, renal and liver profiles and urinalysis; normal eosinophils do not exclude chronic infection.
02
Schistosome serology
Why
Detect infection in travellers whose egg burden is too low for routine microscopy.
Interpretation and limitations
Test after the laboratory-recommended window, commonly at least eight weeks after last exposure; antibodies may persist after cure and do not identify species or active egg excretion.
03
Midday terminal urine microscopy
Why
Demonstrate S. haematobium eggs and assess urogenital infection.
Interpretation and limitations
Collect terminal urine around late morning to early afternoon, preferably after exercise, and use filtration or concentration; repeated specimens increase sensitivity.
04
Concentrated stool microscopy
Why
Find and speciate intestinal schistosome eggs while identifying other helminths.
Interpretation and limitations
Send at least three specimens collected on separate days when suspicion persists; a negative series does not fully exclude low-burden traveller infection.
05
Reference PCR or antigen assay
Why
Support active-infection assessment when microscopy and serology are discordant or species is uncertain.
Interpretation and limitations
Availability and validated specimen type vary; discuss with a tropical or reference laboratory rather than treating an unvalidated molecular result as a universal gold standard.
06
Urinary tract imaging and cystoscopy
Why
Assess obstruction, calcification, bladder-wall disease or malignancy in urogenital schistosomiasis.
Interpretation and limitations
Ultrasound identifies hydronephrosis and bladder abnormalities; persistent haematuria or a focal lesion needs urology and tissue diagnosis rather than attribution to parasites alone.
07
Liver and portal assessment
Why
Stage periportal fibrosis, splenomegaly and portal-hypertension complications.
Interpretation and limitations
Ultrasound with portal evaluation, FBC, synthetic function and endoscopy when indicated distinguishes presinusoidal schistosomal portal hypertension from primary cirrhosis.
08
Urgent MRI brain or spine
Why
Locate inflammatory granulomas, cord swelling or compressive mimics in neurological disease.
Interpretation and limitations
MRI patterns are not pathogen-specific; combine imaging with exposure, eosinophilia and serology, and avoid unsafe lumbar puncture when mass effect or cord compression is possible.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Strongyloidiasis

Eosinophilia, rash and gastrointestinal symptoms overlap, but larva currens, autoinfection risk and serology or stool larvae distinguish Strongyloides.

Urinary tract pathology

Bacterial infection, stones, glomerular disease and bladder cancer also cause haematuria and require urine culture, renal assessment and imaging.

Inflammatory bowel disease

Chronic diarrhoea, bleeding and abdominal pain resemble intestinal schistosomiasis; endoscopic biopsy may reveal eggs or an alternative inflammatory pattern.

Chronic liver disease

Viral, metabolic and alcohol-related cirrhosis can cause portal hypertension, usually with a different parenchymal and synthetic-function profile.

Spinal compression

Tumour, epidural abscess, tuberculosis and disc disease can cause acute myelopathy and must be excluded urgently by MRI.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01SCREENEvaluate freshwater exposureFirst stepA traveller or migrant reports skin contact with untreated freshwater in a schistosomiasis-risk region.

1Record the country, water body, exposure date and duration, then ask about rash, fever, cough, bowel, urinary, genital and neurological symptoms.
2Request FBC with eosinophils and plan serology after the appropriate post-exposure interval; symptomatic or eosinophilic patients need earlier specialist assessment.
3Add repeated targeted urine or stool microscopy when maturation time, species geography and symptoms make egg excretion plausible.
4Investigate organ symptoms directly rather than assuming that a future serology result will explain haematuria, bleeding, neurological deficit or portal signs.

02ACUTEManage Katayama syndromeSystemic febrile illness and eosinophilia develop weeks after a substantial first freshwater exposure.

1Exclude malaria, bacterial sepsis and other travel infections while assessing respiratory, neurological, cardiac and hepatic involvement.
2Discuss urgently with tropical medicine because praziquantel kills mature worms poorly and antigen release can temporarily intensify inflammatory illness.
3Use specialist-directed systemic corticosteroids for clinically significant Katayama disease, particularly organ involvement, with a defined taper and infection-risk assessment.
4Time praziquantel and any repeat dose to parasite maturation and response; do not regard one early course as guaranteed eradication.

03TREATClear mature schistosome infectionTesting and exposure support established infection without an acute neurological emergency.

1Confirm likely species, pregnancy status, weight, interacting anticonvulsants and organ complications before selecting the total praziquantel dose.
2For S. haematobium or S. mansoni, commonly give 40 mg/kg orally in two divided doses during one day with food under a specialist-informed plan.
3For S. japonicum or S. mekongi, use the service protocol, often 60 mg/kg in two or three divided doses over one day, rather than extrapolating blindly.
4Consider repeat treatment after four to eight weeks when exposure was recent, egg burden high, symptoms persist or post-treatment tests remain positive.

04ORGANSAddress chronic complicationsHaematuria, genital symptoms, bowel bleeding, portal hypertension or focal organ abnormalities accompany infection.

1Refer haematuria, obstruction or bladder-wall abnormality to urology; exclude stones, glomerular disease and malignancy even when eggs are demonstrated.
2Coordinate hepatology and endoscopy for varices or portal-hypertension complications while preserving awareness that synthetic function may remain normal.
3Use sexual-health, gynaecology or fertility services for genital disease, including assessment for HIV and other infections where clinically appropriate.
4Treat parasites but explain that established fibrosis, varices or malignant change may require continuing organ-specific surveillance and intervention.

05NEURORespond to neurological diseaseA compatible exposure is followed by cord, cauda-equina, seizure or focal cerebral features.

1Arrange emergency MRI of the relevant neuraxis and involve neurology, tropical infection and spinal or neurosurgical teams according to findings.
2Begin specialist-directed high-dose corticosteroid therapy promptly when inflammatory neuroschistosomiasis is likely; delay can leave permanent disability.
3Give praziquantel within the coordinated plan, usually with steroid cover, recognising that parasite antigen release can worsen inflammation.
4Monitor respiratory function, bladder and bowel function, pressure injury, thrombosis and rehabilitation needs while confirming the diagnosis.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Treatment of choice for mature urinary or intestinal schistosome infection and prevention of further egg-mediated organ damage.

Praziquantel for S. haematobium or S. mansoni

Give a total of 40 mg/kg orally with food over one day, commonly divided as 20 mg/kg followed by 20 mg/kg four to six hours later.

Dizziness and gastrointestinal or inflammatory symptoms are common; anticonvulsants can lower exposure, immature worms respond poorly, and neurological or acute Katayama disease needs steroid-covered specialist timing.

Species-adjusted treatment for Asian schistosomes with higher egg output and a greater potential for disseminated disease.

Praziquantel for S. japonicum or S. mekongi

Use a specialist-confirmed total of 60 mg/kg orally with food over one day, divided into two or three doses separated by approximately four to six hours.

Confirm species and local protocol because published schedules vary; review pregnancy, interacting enzyme-inducing medicines and possible cerebral involvement before treatment.

Suppresses dangerous host inflammation in acute Katayama syndrome and neuroschistosomiasis while definitive antiparasitic treatment is coordinated.

Systemic corticosteroid for inflammatory disease

Use a tropical-infection and neurology-directed oral or intravenous regimen matched to Katayama severity or neurological involvement, followed by a planned taper rather than an unsupervised fixed course.

Exclude or cover competing infection, assess Strongyloides risk before prolonged steroid exposure, monitor glucose and gastrointestinal risk, and avoid abrupt withdrawal after extended use.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Obstructive uropathy

Ureteric and bladder fibrosis causes hydroureter, hydronephrosis, recurrent urinary infection, stone formation, progressive pressure damage and eventual renal impairment.

Bladder carcinoma

Long-standing S. haematobium inflammation increases squamous-cell carcinoma risk, so persistent haematuria or a lesion demands tissue assessment.

Portal hypertension

Periportal fibrosis produces splenomegaly, hypersplenism, abdominal collateral vessels and life-threatening variceal haemorrhage despite initially preserved hepatocellular synthetic function.

Neurological disability

Cord, cauda-equina or cerebral granulomas can leave weakness, sensory loss, epilepsy, pain and permanent bladder or bowel dysfunction.

Genital and reproductive disease

Egg fibrosis can cause infertility, ectopic pregnancy, dyspareunia, bleeding and lesions that may facilitate sexual transmission of HIV.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Review symptoms and eosinophil count after therapy, recognising that transient inflammatory worsening can follow praziquantel and that eosinophils may fall slowly.
When eggs were demonstrated, repeat targeted urine or stool examination at a specialist-defined interval, often one to three months, to assess ongoing excretion.
Consider repeat serology only for a defined laboratory question; antibodies can remain positive long after cure and are not a simple test-of-cure.
Re-image hydronephrosis, bladder lesions, periportal fibrosis or splenomegaly according to the organ pathway rather than ending care when antiparasitic tablets finish.
After neurological disease, track power, sensation, mobility, continence, pain and rehabilitation goals, with repeat MRI when the specialist team expects it to change management.
Document advice to avoid future endemic freshwater exposure and ensure any similarly exposed companions receive individual risk assessment rather than shared empirical treatment.
Persistent haematuria, gastrointestinal bleeding or genital symptoms after parasitological treatment warrants renewed structural and malignant-disease evaluation.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Eggs cause most damage

Adult worms can remain clinically quiet while retained eggs provoke granulomas, fibrosis and progressive urinary, bowel, hepatic or neurological injury.

Testing has a maturation clock

Serology and egg detection may be negative soon after freshwater contact, so the last exposure date determines when screening becomes reliable.

Terminal urine improves yield

S. haematobium eggs are most likely in a concentrated terminal midday specimen, especially after activity, rather than an arbitrary early-morning sample.

Portal hypertension is presinusoidal

Severe varices and splenomegaly may coexist with preserved albumin and clotting because periportal obstruction precedes hepatocyte failure.

Early praziquantel can miss worms

Activity is greatest against mature parasites, making planned repeat therapy important after very recent exposure or treatment during Katayama illness.

Scope boundary

Schistosome-specific testing and organ patterns are emphasised here; evaluation of eosinophilia for Strongyloides, filariae and other helminths remains a parallel pathway.

11Common pitfallsFrequent interpretation and management errors.

01
Do not screen immediately after swimming and declare infection excluded; record the date and arrange testing after the diagnostic window.
02
Do not request one generic stool sample for suspected S. haematobium; collect targeted midday terminal urine and repeat appropriately.
03
Do not interpret eosinophilia as mandatory or specific; chronic schistosomiasis may have a normal count and many other conditions elevate eosinophils.
04
Do not give praziquantel alone without urgent imaging and steroid planning when spinal or cerebral schistosomiasis is suspected.
05
Do not assume haematuria is benign because exposure occurred; urinary malignancy, stones and renal pathology still require standard investigation.
06
Do not use persistent antibody as proof of active treatment failure, because serology can remain reactive after parasite clearance.
07
Do not forget Strongyloides assessment before substantial corticosteroid therapy in someone who has lived in or travelled through endemic regions.