Trematode

Trematodes, commonly known as flukes, are a class of parasitic flatworms (phylum Platyhelminthes). They inhabit a wide range of vertebrate hosts, including humans, and are characterized by a leaf- or knob-shaped body with a syncytial tegument that resists host digestion and immune attack. Most trematodes are hermaphroditic, but several species, notably the blood flukes of the genus Schistosoma, are dioecious with distinct male and female individuals.

Morphology and attachment: Trematodes typically possess two muscular suckers—a mouth-based oral sucker and a ventral acetabulum—used for feeding and attachment to host tissues. The tegument is thick and multicellular in some forms, with spines or projections in others. The body is usually flattened and unsegmented.

Life cycles are complex and typically involve one or more intermediate hosts, usually freshwater snails. Eggs hatch into free-swimming miracidia, which infect snails and develop into sporocysts and rediae. These give rise to cercariae, which leave the snail and either directly infect the vertebrate definitive host or encyst as metacercaria in second hosts or the environment.

Ecology and disease: Humans acquire infections by ingesting metacercaria in undercooked fish (Clonorchis, Opisthorchis) or via water-borne exposure, or by skin penetration of cercariae (schistosomes). Other significant trematodes include Fasciola hepatica and F. gigantica (fascioliasis) in livestock and humans. They commonly inhabit liver or biliary ducts, intestines, or blood vessels.

Medical and veterinary significance: Diagnosis relies on eggs in stool or urine, serology, or imaging. Treatment typically uses praziquantel, with varying efficacy for different species. Prevention emphasizes snail control, sanitation, safe food handling, and reducing exposure to contaminated water.