Schistosomiasis
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Direct answer
Schistosomiasis is a chronic infection caused by blood flukes of the genus Schistosoma, which live as adults in the venules of the bladder and bowel. The clinical pattern depends on the species and on where its eggs lodge in tissue, and praziquantel is the drug of choice for all major species. Infection follows skin contact with freshwater that contains cercariae released by infected snails.
What you must remember
- Causative species: S. haematobium, S. mansoni and S. japonicum are the main human pathogens, with S. mekongi and S. intercalatum seen less often.
- Intermediate hosts: Bulinus for S. haematobium, Biomphalaria for S. mansoni and Oncomelania for S. japonicum.
- Egg spine: terminal in S. haematobium, lateral in S. mansoni and a small lateral knob in S. japonicum.
- Katayama fever: an acute febrile illness with eosinophilia, typically weeks after freshwater exposure.
- Terminal haematuria: the classic urinary feature of S. haematobium infection, often seen at the end of micturition.
- Malignancy: squamous cell carcinoma of the bladder is linked to long-standing S. haematobium infection.
- Diagnosis: urine microscopy for eggs in urinary disease, Kato-Katz stool examination for intestinal species, and antibody or antigen tests in travellers.
- Drug of choice: praziquantel, which is effective against all major species.
Matching species to egg, host and clinical picture
Schistosomiasis questions usually turn on linking one species to its egg, snail host and organ of damage. The table gives the comparison most often tested in NEET-PG.
| Species | Egg spine | Snail host | Main clinical picture |
|---|---|---|---|
| S. haematobium | Terminal | Bulinus | Haematuria, bladder fibrosis, bladder carcinoma |
| S. mansoni | Lateral | Biomphalaria | Intestinal polyps, periportal fibrosis |
| S. japonicum | Small lateral knob | Oncomelania | Hepatosplenic disease, periportal fibrosis |
Egg morphology is the most reliable clue in a microscopy question, because the spine position identifies the species before any clinical detail is considered. Periportal fibrosis leads to portal hypertension, which is the hepatosplenic complication most often tested. Eggs trapped in tissue provoke granulomas, and it is this granulomatous response, rather than the adult worms themselves, that causes most of the organ damage.
Where the exam tries to catch you
Most schistosomiasis traps come from matching the wrong species to the presenting feature.
- Trap: choosing S. mansoni for a child with haematuria Correct: haematuria with terminal-spined eggs points to S. haematobium, the urinary species.
- Trap: searching for eggs in stool for a urinary complaint Correct: S. haematobium eggs are passed in urine, and a midday urine sample improves the yield.
- Trap: believing Katayama fever is a chronic hepatosplenic stage Correct: it is an acute febrile syndrome early in infection, often with marked eosinophilia.
Frequently asked questions
Which Schistosoma species causes haematuria and bladder cancer?
S. haematobium causes terminal haematuria and is the species linked to squamous cell carcinoma of the bladder in chronic infection. Its eggs have a terminal spine and are found in urine on microscopy.
Why is midday urine used to detect Schistosoma haematobium eggs?
Eggs are released into urine in larger numbers around midday, often after physical exertion, so a midday sample improves the yield. A single negative sample does not exclude infection, so repeated collection may be needed.
What is Katayama fever?
Katayama fever is an acute syndrome of fever, malaise and eosinophilia that develops weeks after exposure to infested freshwater. It reflects the host immune response to early worm antigens and eggs, and it is distinct from chronic hepatosplenic disease.
Which drug is the treatment of choice for schistosomiasis?
Praziquantel is the drug of choice for schistosomiasis and is effective against adult worms of all major species. It is usually given as a short oral course, and follow-up examination of urine or stool confirms clearance.
Is schistosomiasis endemic in India?
India is not generally considered endemic for schistosomiasis, so exam questions usually present it as an imported infection in a traveller from Africa or the Middle East. Diagnosis in such a patient relies on the same urine or stool microscopy, supported by serology.