Schistosomiasis (Bilharzia) – Causes, Symptoms, Treatment
Schistosomiasis, also known as bilharzia, is a parasitic tropical disease caused by flatworms of the genus Schistosoma, primarily affecting the liver, intestines, and urinary tract.
Things worth knowing about "Schistosomiasis"
Schistosomiasis, also known as bilharzia, is a parasitic tropical disease caused by flatworms of the genus Schistosoma, primarily affecting the liver, intestines, and urinary tract.
What is Schistosomiasis?
Schistosomiasis, also commonly referred to as bilharzia, is one of the most widespread parasitic infectious diseases in the world. It is caused by parasitic flatworms (trematodes) of the genus Schistosoma. The disease is endemic in tropical and subtropical regions of Africa, Asia, and South America, affecting an estimated 200 to 250 million people worldwide. The WHO classifies schistosomiasis as a neglected tropical disease (NTD).
Causes and Transmission
Infection occurs through direct skin contact with contaminated freshwater containing free-swimming larvae known as cercariae. These larvae actively penetrate human skin within minutes of contact. Freshwater snails serve as intermediate hosts, in which the larvae develop before being released into the water.
- Schistosoma mansoni and Schistosoma japonicum: Cause the intestinal and hepatic (liver-intestinal) form of the disease
- Schistosoma haematobium: Causes the urogenital form, primarily affecting the bladder
At-risk populations include people who live or work near freshwater bodies in endemic regions, including farmers, fishermen, and children who swim or bathe in infested water.
Symptoms
Early Phase (Acute Schistosomiasis)
- Itching and skin rash at the site of larval penetration (cercarial dermatitis, also known as swimmer's itch)
- Fever, chills, and general malaise
- Cough, muscle aches, and fatigue
- Katayama syndrome: an acute serum sickness-like reaction with fever and elevated eosinophils, occurring 4 to 6 weeks after initial infection
Chronic Phase
- Intestinal form: Abdominal pain, diarrhea, blood in the stool, hepatomegaly (enlarged liver), splenomegaly (enlarged spleen), and liver fibrosis
- Urogenital form: Blood in the urine (hematuria), painful urination, bladder fibrosis, and an increased risk of bladder cancer
- Long-term complications: malnutrition, anemia, and growth retardation in children
Diagnosis
Schistosomiasis can be diagnosed using several approaches:
- Microscopic examination: Detection of Schistosoma eggs in stool or urine samples
- Serological tests: Detection of antibodies against Schistosoma antigens in the blood
- Imaging: Ultrasound to assess changes in the liver, spleen, or bladder
- Blood count: Elevated eosinophil levels (a type of white blood cell) are a common indicator of a parasitic infection
Treatment
The drug of choice for treating schistosomiasis is praziquantel. This antiparasitic medication is effective against all Schistosoma species pathogenic to humans and is typically administered as a single oral dose or over two days. Praziquantel is most effective against adult worms but less active against immature larvae.
- Supportive treatment may be required for patients with severe organ damage
- Corticosteroids may be used in cases of acute Katayama syndrome
- Mass drug administration (MDA) programs with praziquantel are a key component of the global control strategy in endemic regions
Prevention
As there is currently no licensed vaccine against schistosomiasis, prevention relies on behavioral and environmental measures:
- Avoid contact with potentially contaminated freshwater in endemic regions
- Do not swim, wade, or bathe in slow-moving or stagnant water in at-risk areas
- Improve access to safe drinking water and sanitation facilities
- Control of snail intermediate host populations
- Travelers to tropical regions should seek medical advice before departure
References
- World Health Organization (WHO): Schistosomiasis Fact Sheet. Geneva, 2023. Available at: https://www.who.int/news-room/fact-sheets/detail/schistosomiasis
- Gryseels B, Polman K, Clerinx J, Kestens L: Human schistosomiasis. The Lancet. 2006;368(9541):1106-1118.
- Centers for Disease Control and Prevention (CDC): Schistosomiasis. Atlanta, 2023. Available at: https://www.cdc.gov/parasites/schistosomiasis/
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