Overview

Schistosomiasis, also known as bilharzia, is a parasitic disease caused by flatworms called schistosomes. It primarily affects people in tropical and subtropical regions, especially in areas with poor sanitation and limited access to clean water. Schistosomiasis is considered one of the most significant neglected tropical diseases, impacting millions worldwide. The infection occurs when humans come into contact with freshwater contaminated by schistosome larvae, which penetrate the skin and migrate through the body. While some people experience mild symptoms, chronic schistosomiasis can lead to serious organ damage, particularly to the intestines, liver, bladder, and urinary tract.

Causes

Schistosomiasis is caused by infection with parasitic worms of the genus Schistosoma. The main causes and risk factors include:

• Parasite species: Common species include Schistosoma mansoni (intestinal), Schistosoma haematobium (urinary), and Schistosoma japonicum (intestinal), with other species present in specific regions.
• Contaminated freshwater: Lakes, rivers, and irrigation canals harbor the parasite’s larvae, released by infected freshwater snails.
• Skin penetration: The larvae, called cercariae, penetrate human skin during activities like swimming, bathing, or washing clothes in contaminated water.
• Poor sanitation: Infected individuals release parasite eggs through feces or urine, which contaminate freshwater and continue the transmission cycle.
• Occupational and recreational exposure: Farmers, fishermen, and children in endemic regions are at higher risk due to frequent water contact.

Symptoms

Symptoms of schistosomiasis vary based on the stage of infection and parasite species:

• Initial symptoms (within days): Skin rash or itchy skin, known as “swimmer’s itch,” shortly after cercariae penetrate the skin.
• Acute stage (2-8 weeks): Also called Katayama fever, symptoms include fever, chills, muscle aches, fatigue, cough, and abdominal discomfort.
• Chronic stage (months to years): Long-term infection causes more severe problems:
  • Intestinal schistosomiasis: Abdominal pain, diarrhea, blood in stool, liver enlargement, and portal hypertension.
  • Urinary schistosomiasis: Frequent urination, painful urination, blood in urine (hematuria), and risk of bladder damage or cancer.
  • Genital schistosomiasis: Lesions in reproductive organs, infertility, and increased risk of HIV transmission, particularly in women.

Diagnosis

Schistosomiasis is diagnosed using a combination of clinical evaluation, laboratory tests, and imaging studies:

• Stool and urine examination: Microscopic identification of parasite eggs in stool (intestinal) or urine (urinary) samples is the standard diagnostic method.
• Serological tests: Blood tests can detect antibodies or antigens associated with schistosome infection, useful in low-endemic areas or early infection.
• Polymerase Chain Reaction (PCR): Advanced molecular techniques can detect schistosome DNA, offering high sensitivity.
• Rectal or bladder biopsy: In chronic or difficult cases, tissue biopsies may be performed to detect eggs embedded in tissues.
• Ultrasound: Imaging helps assess organ damage, especially in the liver and urinary tract, in chronic cases.

Treatment

Treatment for schistosomiasis is effective and typically involves antiparasitic medications:

• Praziquantel: The drug of choice for all forms of schistosomiasis. It is administered as a short course and kills adult worms, reducing disease severity.
• Repeat dosing: In high-risk areas or severe infections, repeat doses may be required to clear residual or newly matured parasites.
• Corticosteroids: May be prescribed in cases with severe inflammatory reactions like Katayama fever.
• Supportive care: Management of complications such as anemia, liver fibrosis, or urinary tract damage is essential in chronic disease.
• Surgical intervention: In advanced cases with organ damage, surgery may be necessary to address complications like bladder obstruction or varices from portal hypertension.

Prognosis

With early diagnosis and proper treatment, schistosomiasis has a good prognosis, and most patients recover without long-term consequences. Treatment with praziquantel effectively clears the infection and reduces the risk of complications.

However, untreated or repeated infections can lead to serious health problems, including liver fibrosis, portal hypertension, bladder cancer, kidney failure, and infertility. Regular screening and mass drug administration programs in endemic areas have significantly reduced the disease burden.

Prevention through improved sanitation, health education, snail control, and avoidance of contaminated water are key strategies to control schistosomiasis. Overall, with proper management, long-term outcomes are favorable for most individuals.