Trematodes (flukes) !
- Parasites
Leaf-shaped flatworms that need a snail to complete their cycle. They arrive with raw plants, fish or crabs, or through the skin in fresh water.
Updated 2026-11-01
What they are
Trematodes are unsegmented flatworms with suckers. All pass through a freshwater snail, where they multiply. Foodborne flukes are acquired by eating metacercariae on aquatic plants, fish or crustaceans; Schistosoma enters through the skin.
What they share
- Flat, leaf-shaped body with oral and ventral suckers.
- Freshwater snail as the first intermediate host.
- Operculated eggs (except Schistosoma, which has a spine).
- Hermaphroditic, except Schistosoma, which has separate sexes.
Microorganisms in this group
- Fasciola hepaticaA flatworm of livestock that reaches humans through raw watercress or other water plants. It tunnels through the liver and lives in the bile ducts.Exam priority: medium
- Schistosoma mansoni / S. haematobium / S. japonicumA worm that enters through the skin when bathing in fresh water with infected snails. Its eggs damage the liver, bowel or bladder.Exam priority: medium
- Paragonimus spp.A flatworm that comes with raw freshwater crabs or crayfish and settles in the lung. It causes bloody cough and is mistaken for tuberculosis.For completeness
- Clonorchis sinensis / Opisthorchis spp.Liver flukes from raw freshwater fish in Asia. They live for years in the bile ducts and raise the risk of bile duct cancer.For completeness
Test yourself
Think of the answer, then tap the question to see it.
Which intermediate host do all trematodes share?
A freshwater snail.
Which trematode does not respond to praziquantel?
Fasciola hepatica, which is treated with triclabendazole.
Which trematode enters the body through the skin?
Schistosoma, whose cercariae penetrate the skin in fresh water.
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Foodborne trematode infections (WHO, 2021); Schistosomiasis (WHO, 2026); CDC - DPDx - Fascioliasis (CDC, 2019).
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Representative model, for educational purposes only.