Schistosomiasis Life Cycle: Stages & Prevention

vcxSchistosomiasis is a parasitic disease caused by flatworms that belong to the Schistosomatidae family. The life cycle of schistosomes includes asexual reproduction in snails and sexual reproduction in mammals.

• It is spread by contact with contaminated freshwater.
• The disease was first discovered by Theodor Bilharz in the 1850s.
• Schistosomiasis is common in areas with poor hygiene and infrastructure.
• This disease is also known as snail fever, Bilharzia, and Katayama fever.
• Symptoms of this infection include abdominal pain, diarrhoea, bloody stool, and blood in the urine.
• A long-term infection can lead to kidney failure, infertility, liver damage, and cancer.
• Diagnosis of schistosomiasis can be done using the Kato-Katz and miracidium hatching test (MHT).
• Control measures include vaccines, drugs, and genetic manipulation techniques.
• Schistosomiasis is a global epidemic affecting over 200 million people annually, in Asia, Africa, South America, and the Caribbean.
• The Schistosomiasis Life Cycle is a complex process that involves both the human host and a freshwater snail.

Read Also:- Human Health and Diseases

Key terms: Flatworm, Snail fever, Bilharzia, Katayama fever, Kidney failure, Infertility, Liver damage, Cancer, Schistosomes

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Life Cycle of Schistosomiasis

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The Schistosomiasis Life Cycle takes about 4 to 6 weeks to complete, depending on the species of schistosome involved. Schistosomes have a complex life cycle. There are three species of Schistosoma that are parasitic on human beings.

1. S. haematobium
2. S. japonicum
3. S. mansoni

The different stages of the schistosome life cycle are – 

1st stage: The Egg stage

• Female fluke, up to 25mm in length, releases around 3500 eggs daily into the bloodstream.
• The number of eggs depends on the species of the worm.
• Eggs are released into freshwater through human urine or feces.
• This marks the beginning of the life cycle of schistosomiasis.
• The eggs hatch, giving rise to larvae known as miracidia.
• These miracidia play a crucial role in the continuation of the life cycle.

Life Cycle of Schistosomiasis

2nd stage: The larval stages

The second stage of the Schistosomiasis Life Cycle is further divided into three steps:

A. Miracidium

• Eggs hatch, releasing miracidia larvae under the appropriate conditions.
• Miracidia are ciliated larvae that swim to intermediate hosts, freshwater snails.
• The specific snail species depends on the Schistosoma species

B. Cercarie

• Two successive sporocysts develop within snails.
• Sporocysts generate cercariae, which is a fork-tailed larvae.
• Cercariae leave snails to enter the water.
• Upon contact with humans, cercariae lose tails, becoming schistosomula.
• Schistosomula feeds on the host's blood.
• Miracidia transform into cercariae within snails.
• Cercariae actively seek a human host when released in water.

C. Schistosomulae

• Schistosomula travel through the lungs, heart, and liver for development through venous circulation.
• Maturity is achieved in the liver, forming separate male and female adults.
• Cercariae enter human skin through contact with contaminated water.
• Cercariae transform into schistosomulae inside the human body.

3rd stage: Adult stage

• Adult worms, male and female, mate in the intestines.
• Females require the presence of male worms to mature.
• Adult worms move within the human body, changing locations.
• Fertilized female worms produce eggs.
• Eggs are released through faeces and urine.
• Schistosomulae migrate through the bloodstream.
• They mature into adult worms, completing the life cycle.

Life Cycle of Schistosomiasis

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Symptoms of Schistosomiasis

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While many infected individuals may remain asymptomatic, those who do develop symptoms typically experience them 4-7 weeks post-infection. 

• Initial symptoms include a general feeling of weakness and minor skin irritation or rash (swimmer rash) when cercariae enters the skin.
• Subsequent symptoms, appearing 2 to 10 weeks later, may include aching, fever, cough, diarrhoea, chills, or gland enlargement.
• The movement of adult worms and their eggs through the body can lead to severe complications.
• Eggs reaching the brain or spinal cord may cause seizures, paralysis, or spinal cord inflammation.
• Symptoms of chronic schistosomiasis include abdominal pain, swelling, bloody diarrhoea, blood in stools or urine, chest pain, and lesions in the vulva or perianal area.

Symptoms of Schistosomiasis

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Prevention of Schistosomiasis

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To prevent Schistosomiasis following measures can be followed – 

• Avoid contaminated water bodies where schistosomiasis is present.
• Practice good hygiene, including washing hands thoroughly.
• Use proper sanitation facilities to prevent contamination of water sources.
• In endemic areas, individuals may take prescribed medications to prevent infection.
• Raise awareness about the disease and its preventive measures in affected communities.
• Implement strategies to reduce the population of snails, the intermediate hosts of the parasite.

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Things to Remember

• Schistosomiasis is caused by parasitic flatworms, leading to symptoms like abdominal pain, diarrhoea, and blood in urine or stool.
• The life cycle begins with eggs released in human stool or urine, entering water.
• In water, eggs hatch into miracidia larvae, which swim and enter a snail.
• Inside the snail, miracidia transform into cercaria larvae.
• Cercariae are released into water, penetrating human skin and becoming schistosomula.
• Schistosomula travel to the liver, mature into adults, and pair up in veins of the intestine or bladder.
• Females lay eggs, which are released through faeces or urine, continuing the life cycle of schistosomiasis.

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