56. Genus Schistosoma. Sch. haematobium. Sch. japonicom, Sch. mansoni · Human Biology · MU Plovdiv

Genus Opisthorchis

The genus Opisthorchis includes parasitic flatworms that belong to the Class Trematoda and the Phylum Platyhelminthes.
Two major species of medical importance are:
Opisthorchis viverrini, which is found mainly in Southeast Asian countries such as Thailand, Laos, Cambodia, and Vietnam.
Opisthorchis felineus, which is found in parts of Europe and Central Asia, including Italy, Germany, Belarus, Russia, Kazakhstan, and Ukraine.
These two species are very similar in both structure and behavior.

Adult Opisthorchis flukes are small and flattened, measuring between seven millimeters and twelve millimeters in length.
They inhabit the bile ducts of their definitive hosts.

Adult worms lay eggs that are passed out of the host through feces.
These eggs are ingested by a snail, which serves as the first intermediate host.
Inside the snail, the parasite undergoes several stages of development:
The egg hatches into a miracidium.
The miracidium becomes a sporocyst, which develops into rediae, and eventually into cercariae.
The cercariae exit the snail and penetrate freshwater fish, which serve as the second intermediate host.
Inside the fish, the cercariae form metacercariae, which encyst in the muscles or beneath the scales.
These metacercariae represent the infective stage for mammals.
Mammals, including humans, cats, and dogs, become infected by eating raw or undercooked fish containing these metacercariae.
Once ingested, the parasites excyst in the duodenum and migrate into the bile ducts, where they mature into adults.

Most infections in humans are asymptomatic.
In some cases, pathology occurs due to inflammation and obstruction of the bile ducts, which may result in abdominal pain, liver dysfunction, or secondary bacterial infections.
The geographical range of opisthorchiasis overlaps with that of fascioliasis in some regions, particularly in parts of Europe and Asia.