trematod

Trematodes, commonly known as flukes, are a class of parasitic flatworms within the phylum Platyhelminthes. They include species with complex life cycles that typically involve one or more intermediate hosts and a definitive vertebrate host. Most trematodes are endoparasites of mammals, birds, and other vertebrates, and many are hermaphroditic, although some species, such as the blood flukes (Schistosoma), are dioecious with distinct male and female individuals.

Morphology and life cycles are varied but share features such as a leaf-shaped body, a oral sucker, and a ventral sucker or acetabulum used for attachment and feeding. The tegument, a syncytial outer covering, facilitates nutrient uptake and protects against host defenses. Trematodes exhibit diverse life cycles that typically begin with eggs released into the environment, progressing through stages such as miracidium, sporocyst, redia, and cercaria, with metacercariae forming in an intermediate host. Transmission to the vertebrate host often occurs by ingestion of contaminated water or raw or undercooked intermediate hosts, or by skin penetration by cercariae.

Medical and veterinary relevance is significant. Human diseases include schistosomiasis caused by Schistosoma species, liver fluke infections by Fasciola hepatica and Opisthorchis/Fasciola spp., and lung fluke infections by Paragonimus species. Eggs deposited by adults cause tissue inflammation and organ dysfunction. Diagnosis generally relies on detecting eggs in stool or urine, supported by serology or imaging. Praziquantel is the broad-spectrum treatment of choice for most trematodes, with alternatives such as triclabendazole used for fascioliasis. Prevention focuses on improved sanitation, snail control, and avoiding consumption of undercooked aquatic hosts.