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Questions and Answers
What is the primary host of Fasciola hepatica?
Which of the following trematodes is not acquired through ingestion of infective metacercariae?
What is the primary habitat of the adult Fasciolopsis buski trematode?
Which of the following Schistosoma species is most prevalent in Africa and the Middle East?
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How do cercariae penetrate the host in Schistosomiasis?
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Where do Schistosoma eggs become trapped in the host?
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What is the number of people infected with Schistosomiasis worldwide?
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What is the percentage of Schistosomiasis cases in sub-Saharan Africa?
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What is the result of Schistosoma infection?
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What is a common symptom of Urinary Schistosomiasis?
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Which test is used for diagnosis of all species of Schistosoma?
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What is the effective treatment against all species of Schistosoma?
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How can the transmission of Schistosomiasis be prevented?
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What is a consequence of untreated Intestinal Schistosomiasis?
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Study Notes
Trematodes (Flukes)
- Fasciolopsis buski: a common intestinal parasite of humans and pigs in South-east Asia, 8cm in length, causes inflammation, ulceration, and hemorrhage of the small intestine.
- Fasciola hepatica (liver fluke): primarily infects sheep, but humans become infected by ingesting metacercariae on watercress, leading to "fascioliasis" and severe anemia.
- Clonorchis sinensis (liver fluke): widespread in China, Japan, Korea, and Taiwan, acquired by ingesting metacercariae in raw or pickled fish.
- Paragonimus westermani (lung fluke): widespread in the Far East and South-east Asia, acquired by ingesting metacercariae in raw or pickled crustaceans.
Schistosomiasis (Bilharzia)
- 200 million people infected in 74 countries, with 85% living in sub-Saharan Africa.
- Three main species: S. haematobium, S. mansoni, and S. japonicum.
- S. haematobium: most prevalent in Africa and the Middle East.
- S. mansoni: found in Africa and Latin America.
- S. japonicum: found in the Pacific region.
Life Cycle
- Transmission occurs through fresh water.
- Infective cercariae released from snails of the genera Bulinus, Biomphalaria, and Oncomelania.
- Cercariae penetrate human skin through contact with infected water.
- Adult worms live in veins that drain the urinary system (S. haematobium) or mesenteric blood vessels (S. mansoni, S. japonicum) and release eggs into water in urine or feces.
- Eggs develop into miracidia, which infect snails.
Pathology
- Schistosoma eggs become trapped in tissues of the urinary tract (S. haematobium) and intestines (S. mansoni, S. japonicum).
- Inflammatory response and tissue damage occur.
Symptoms and Signs
- Urinary Schistosomiasis:
- S. haematobium: gross hematuria, dysuria, bladder, ureters, and kidney damage, and increased risk of bladder cancer.
- Intestinal Schistosomiasis:
- S. mansoni, S. japonicum: gradual liver and spleen enlargement, hypertension, bleeding of abdominal blood vessels, and blood in stools.
Diagnosis
- Microscopy for eggs: urine sediment for S. haematobium, concentrated stool samples for S. mansoni, S. japonicum.
- Serology: effective for all species.
- Rectal biopsy: effective for S. mansoni, S. japonicum.
Treatment
- Praziquantel: effective against all species.
- S. haematobium: single dose (40 mg/kg).
- S. mansoni, S. japonicum: 2-3 doses of 30 mg/kg.
Prevention and Control
- Educate people to avoid urinating or defecating in fresh water supplies.
- Eliminate snail vectors by making water habitat unsuitable (increased water flow, removing vegetation).
- Provide piped water to avoid direct contact with cercariae.
- Mass drug treatment of communities to reduce reservoir of infection.
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Description
Learn about Fasciolopsis buski and Fasciola hepatica, two common types of trematodes that infect humans and animals, causing inflammation, ulceration, and hemorrhage in the small intestine and liver. Understand their life cycles and habitats.
