trematódeos

Trematodes, commonly known as flukes, are a class of parasitic flatworms within the phylum Platyhelminthes. They are characteristically leaf- or lanceolate-shaped, unsegmented in adults, and covered by a syncytial tegument. Most trematodes are hermaphroditic, possessing both male and female reproductive organs, though some species, notably the blood flukes (Schistosoma), are dioecious with separate sexes.

Their life cycles are complex and typically require a mollusk (usually a snail) as the first intermediate host, and at least one vertebrate host as the definitive host in which sexual reproduction occurs. The life cycle stages commonly include eggs, miracidia, sporocysts, rediae, cercariae, and metacercariae. Transmission to humans or other animals occurs when cercariae penetrate the skin in water or when metacercariae are ingested with undercooked aquatic organisms or contaminated vegetation.

Medical relevance: human trematode infections include schistosomiasis caused by Schistosoma mansoni, S. haematobium, and S. japonicum; fascioliasis caused by Fasciola hepatica and Fasciola gigantica; clonorchiasis and opisthorchiasis caused by Clonorchis sinensis and Opisthorchis spp.; and paragonimiasis. Diseases range from intestinal and biliary disorders to liver, lung, and systemic manifestations, contributing to morbidity in many regions with limited sanitation and freshwater exposure.

Diagnosis and treatment: diagnosis is based on detection of eggs, larvae, or parasite antigens in stool, urine, or tissue samples; serology and imaging may support diagnosis in some cases. Treatment typically uses praziquantel as first line for most trematodes; triclabendazole is preferred for Fasciola infections, and Schistosoma infections are commonly treated with praziquantel as well. Prevention focuses on sanitation, snail control, safe cooking of fish and aquatic plants, and avoiding contact with contaminated water.