Introduction
Schistosomiasis (bilharzia) is a parasitic disease caused by species of Schistosoma. It is a major public health problem common in many tropical and sub-tropical countries, especially areas with limited access of clean water and proper sanitation. The World Health Organization (WHO) considers schistosomiasis one of the neglected tropical diseases (NTDs), affecting over 200 million people worldwide. https://www.cdc.gov/parasites/schistosomiasis/
Types of Schistosoma
there are several species of Schistosoma that infect human the most common include
Schistosoma haematobium: causes urinary schistosomiasis.
Schistosoma mansoni: causes intestinal schistosomiasis.
Schistosoma japonicum: also causes intestinal schistosomiasis, usually more severe.
Schistosoma mekongi: Southeast Asia; similar to S. japonicum
Schistosoma intercalatum: restricted to certain areas of Central Africa, this species causes intestinal schistosomiasis.
Each species has a specific range of intermediate host snails and causes clinical manifestations varying according to organ involvement.
Causes of Schistosoma
Schistosomiasis is due to infection by Schistosoma parasites. Humans get infected when larval forms of the parasite, which are released by freshwater snails, enter the skin when a person comes into contact with contaminated water. Once they’re inside the body, the parasites develop in the blood vessels and lay eggs that lead to inflammation and damage to different organs.
Mode of Transmission
Transmission of schistosomiasis is a complex process that takes place between humans, freshwater snails and contaminated water:
Humans excrete Schistosoma eggs in urine or feces into freshwater.
Eggs hatch in water, giving rise to miracidia that infect certain species of freshwater snails.
Within the snails, the miracidia multiply into and become cercariae, or infective larvae.
Cercariae are released back into the water and penetrate human skin when contact.
Inside the human host, they develop to become adult worms and move to blood vessels where they lay eggs and life cycle continue.
Life Cycle of Schistosoma
Eggs are released from an infected human in urine (S. haematobium) or feces (S. mansoni, S. japonicum).
In fresh water, the eggs hatch into larvae called miracidia, which are swim and search to find and penetrate an appropriate snail host.
Within the snail, the miracidia develop into sporocysts, where they reproduce asexually.
The cercariae are produced by sporocysts and are freed in the water.
The cercariae are capable of penetrating human skin on contact with water and lose their tails to become schistosomulae.
Schistosomulae enter the bloodstream, travel to the liver, mature into adult worms and mate.
Adult worms travel to their final destination:
S. haematobium (bladder veins)
Mesenteric veins (S. mansoni, S. japonicum)
Worms produce eggs that are passed to the bladder or intestine for excretion, restarting the cycle.
🌍Geographical Distribution
Schistosomiasis is endemic in 78 countries, primarily in:
Sub-Saharan Africa: The most impacted region, especially by S. haematobium and S. mansoni.
Middle East and North Africa: Egypt and Yemen.
South America: Primarily Brazil and Venezuela (S. mansoni).
East and Southeast Asia: Highly China and the Philippines (S. japonicum and S. mekongi).
” The disease thrives in communities that depend on freshwater sources for bathing, washing and agriculture, particularly where sanitation conditions are poor.”
Signs and Symptoms of Schistosoma
Symptoms differ based on the infection stage and the species involved:
Acute Schistosomiasis
Fever
Chills
Cough
Muscle aches
Eosinophilia (increased eosinophils in the blood)
Chronic Schistosomiasis:
Urinary schistosomiasis (S. haematobium):
Blood in urine (hematuria)
Bladder pain
Higher risk of bladder cancer
Intestinal schistosomiasis (S. mansoni, S. japonicum):
Abdominal pain
Diarrhea (possibly bloody)
Hepatosplenomegaly (an enlarged liver and spleen)
fibrosis of liver and portal hypertension)
Diagnosis of Schistosoma
There are several ways to diagnose:
Microscopy: detection of schistosoma eggs in stool or urine samples
Antibody or antigen detection tests: there are serological tests that can detect specific antibodies to Schistosoma species.
PCR testing: Detects Schistosoma DNA in body fluids.
Chronic: Ultrasound or CT scans to evaluate the extent of organ damage.
Cystoscopy: In S. haematobium infections to examine bladder damage and see eggs.
💊Treatment of Schistosoma
The treatment of choice is praziquantel.
Dosage:
Typically, 40–60 mg/kg body weight, in 1 or 2 divided doses.
Mechanism:
It makes parasite cell membranes leaky to calcium, paralyzing and killing the worm.
Effective Against:
all the major species infecting humans:
Schistosoma mansoni
S. haematobium
S. japonicum
🧪 Supportive Measures
Corticosteroids: May be given in cases of severe inflammatory reactions (e.g., spinal cord involvement).
Hydration & Nutrition Significant in heavily infected patients.
Manage any secondary infections (especially S. haematobium in the urinary tract)
📆 Follow-Up
repeat stool/urine exams 6–12 weeks later. to evaluate treatment success
Re-treatment might be required in regions of high transmission, or if infection persists.
Risk Factors
There are a few things that make you more likely to get infected:
Residing in or visiting endemic regions.
Frequent exposure to infected fresh water (e.g swimming, fishing, agriculture)
Lack of sanitation and hygiene practices
No access to clean water.
Occupational (e.g., rice farmers, fishermen)
Children are particularly vulnerable due to frequent water play and less awareness of prevent.
Prevention
Some effective strategies to prevent this are:
Public Health Measures
improving sanitation and clean water access.
Health education campaigns to decrease risky behavior
Snail control to limit the intermediate host population.
Personal Protective Measures:
Refraining from swimming or wading in freshwater in endemic regions.
Of freshwater exposure while wearing protective cloth
Mass Drug Administration (MDA):
Mass drug administration (MDA) program to treat praziquantel at-risk populations. especially school aged children
Regular screening and treatment in endemic areas to reduce transmission.
Conclusion
Schistosomiasis is still a widespread health threat in many parts of the world, particularly where there is limited access to clean water and sanitation. With appropriate preventive measures, community awareness, and access to therapy when necessary, schistosomiasis infection can be controlled and even eliminated in many endemic areas. Sustained investment in public health infrastructure and disease surveillance is the key to long-term success of this neglected tropical disease.
