spargana

Spargana are the plerocercoid larval stage of Spirometra tapeworms. In humans they cause sparganosis, a tissue-invasive zoonosis. The larvae migrate through subcutaneous tissue and can reach muscle, the eye, and the central nervous system.

Life cycle: definitive hosts such as cats and dogs shed eggs in feces; eggs release coracidia that infect copepods. Second intermediate hosts—including fish, amphibians, and reptiles—acquire spargana after ingesting infected copepods. Paratenic hosts such as frogs and snakes may harbor spargana without further development. Humans become infected by drinking water containing infected copepods, by eating raw or undercooked second-intermediate or paratenic hosts, or through exposure to poultices made from infected tissues.

Clinical features vary by location. Most infections are subcutaneous with migratory nodules. Ocular sparganosis can affect the conjunctiva or orbit and impair vision; cerebral sparganosis can cause headaches, seizures, or focal deficits. Diagnosis relies on imaging (ultrasound, CT, MRI), serology, and, when feasible, histology after removal of the larva.

Treatment is mainly surgical removal of the sparganum; praziquantel has limited proven efficacy.

Prevention includes avoiding raw or undercooked second-intermediate or paratenic hosts, not using raw frog or snake tissues as poultices, and ensuring safe drinking water. Sparganosis is most frequently reported in East and Southeast Asia, though cases occur worldwide.