ligula intestinalis in aquatic systems: taxonomy, epidemiology, pathology, and control — a concise narrative review

Ligula intestinalis (cestoda: diphyllobothriidae) is a cosmopolitan tapeworm with a three‑host life cycle involving copepods, cyprinid fishes, and piscivorous birds. its plerocercoid stage grows extensively within the fish's body cavity, compressing the viscera and causing profound reproductive impairment. here we synthesize taxonomy and morphology, life cycle, epidemiology (with emphasis on iran), pathology, zoonotic considerations, and control options. molecular data increasingly support the synonym of digramma with ligula and indicate low interspecific divergence within the complex. regionally, prevalence varies widely (≈3–60% in iran, depending on host, season, and locality) and can reach double‑digit levels in african lakes. gross lesions include abdominal distension and gonadal atrophy; histopathology commonly reveals ovarian/testicular degeneration and hepatic vacuolation. despite sporadic claims, confirmed human infection by l. intestinalis has not been documented; risk is minimized by proper cooking and avoidance of raw freshwater fish. effective control requires interrupting the life cycle (reducing copepods, excluding piscivorous birds from aquaculture), routine monitoring, biosecurity in semi‑closed systems, and public education.