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Bilharziasis – Causes, Symptoms and Treatment

Bilharziasis is a parasitic tropical disease caused by flatworms of the genus Schistosoma, affecting millions of people in Africa, Asia, and South America.

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Things worth knowing about "Bilharziasis"

Bilharziasis is a parasitic tropical disease caused by flatworms of the genus Schistosoma, affecting millions of people in Africa, Asia, and South America.

What is Bilharziasis?

Bilharziasis, also known as schistosomiasis, is a parasitic infectious disease caused by flatworms of the genus Schistosoma. It is the second most prevalent parasitic disease worldwide after malaria, primarily affecting people living in tropical and subtropical regions, particularly in sub-Saharan Africa, South America, the Caribbean, and parts of Asia. The World Health Organization (WHO) estimates that more than 200 million people are infected globally.

Causes and Transmission

Infection occurs through contact with freshwater contaminated with free-swimming larvae called cercariae. These larvae actively penetrate human skin, even through intact skin, without requiring an open wound. The parasite completes its life cycle using freshwater snails as intermediate hosts.

Main species infecting humans: Schistosoma mansoni, Schistosoma haematobium, Schistosoma japonicum
Route of transmission: Contact with contaminated freshwater (swimming, bathing, washing, fishing)
Intermediate host: Freshwater snails of the genera Biomphalaria, Bulinus, and Oncomelania

Symptoms

The disease progresses through several stages, each with distinct clinical features:

Acute Phase (Katayama Fever)

Itchy skin rash shortly after cercariae penetration (cercarial dermatitis or swimmer's itch)
Fever and chills
Cough and muscle aches
Enlarged lymph nodes, liver, and spleen

Chronic Phase

Urogenital schistosomiasis (caused by S. haematobium): blood in urine (haematuria), bladder and kidney damage, increased risk of bladder cancer
Intestinal schistosomiasis (caused by S. mansoni, S. japonicum): abdominal pain, diarrhoea, blood in stool, liver fibrosis, enlarged spleen
Chronic fatigue, malnutrition, and developmental delays in children

Diagnosis

Several diagnostic methods are used to confirm infection:

Microscopic examination: Detection of parasite eggs in urine or stool samples
Serological tests: Blood tests detecting antibodies against Schistosoma (especially useful in travellers and early infections)
Imaging: Ultrasound to assess the liver, spleen, and bladder in chronic disease
PCR testing: Molecular detection of the parasite, increasingly used in modern diagnostics

Treatment

The drug of choice for treating bilharziasis is praziquantel. It is effective against all major Schistosoma species that infect humans and is typically administered orally as a single or divided dose. When diagnosed early, treatment is highly effective.

Standard therapy: Praziquantel (40 mg/kg body weight orally, usually as a single dose or split dose)
In cases with severe complications such as liver fibrosis, additional medical management may be required
Travellers returning from endemic areas should seek medical advice if exposure to freshwater is suspected

Prevention

Since no licensed vaccine is currently available, prevention relies on behavioural measures and public health strategies:

Avoid contact with freshwater in endemic areas
Do not swim, wade, or bathe in potentially contaminated rivers, lakes, or ponds
WHO-supported mass drug administration programmes using praziquantel in endemic regions
Improvement of sanitation facilities and access to clean water

References

World Health Organization (WHO): Schistosomiasis – Fact Sheet. Geneva, 2023. Available at: https://www.who.int/news-room/fact-sheets/detail/schistosomiasis
Gryseels B. et al.: Human schistosomiasis. The Lancet, 2006; 368(9541):1106–1118.
Centers for Disease Control and Prevention (CDC): Schistosomiasis – Parasites. Atlanta, 2023. Available at: https://www.cdc.gov/parasites/schistosomiasis

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