Contents
Introduction
Schistomiasis, also known as Bilharziasis is a disease caused by parasitic flatworms which infect the urinary tract or intestinal tract. It can cause a wide range of symptoms, including abdominal pain, melaena, diarrhoea and haematuria.
It children it can cause poor growth and developmental delay.
It is often acquired in childhood from swimming in freshwater – the parasites are released from infected freshwater snails.
Diagnosis is with serology, or finding of fresh eggs in the stool or urine.
It is treated with the medication praziquantel. In endemic areas, annual doses of this treatment may be given to entire populations.
Organisms
Blood flukes (schistosoma) 3 species most commonly affecting humans:
- S.mansoni
- S.haematobium
- S.japonicum
Life Cycle
Transmission
Spread by fresh water snails
Epidemiology
- Has huge socio-economic consequences in the tropics
- S. haematobium found in Africa and the Middle East
- S. japonicum found in the Far East
- S.mansoni is the most widespread, found mostly in South Americ the Caribbean, Africa the Middle East
Pathogenesis
- Fresh water snail vectors release cercariae that penetrate skin (during swimming/paddling)
- Causes itchy popular rash
- Cercariae shed their tails to become schistosomules migrate to the lungs and liver where they grow into adult form.
- 2 weeks later ‘Katayma fever’ = initial immune reaction to worm maturation and shedding of eggs.
- Approx 2 months later, flukes are mature and migrate to their resting habitats.
Clinical features
Acute: Katayama fever
Complications
S.mansoni and S.japonicum
- Both favour mesentaeric veins
- Lead to intestinal polyps, blood
- Stained stools, hepatic fibrosis and portal hypertension.
S.haematobium
- Favours bladder veins
- Lead to urinary obstruction, polyps and
- Bladder cancer(squamous cell) Hydronephrosis, pyelonephritis, renal failure.
- Transverse myelitis.
Diagnosis
- Microscopy for eggs in stool, urine or biopsy.
- Serology in non-endemic areas
- Eosinophilia
- Renal tract US may be used to assess for complications
Treatment
Praziquantel. Consider referral to renal specialist – especially if any abnormalities on renal ultrasound.
Prevention
Avoidance of fresh water contact in endemic areas.