Anisakis

Anisakis is a genus of parasitic nematodes in the family Anisakidae. Several species are associated with marine life, including Anisakis simplex and Anisakis pegreffii, among others. The genus is of medical and veterinary importance due to its role in human disease and its complex life cycle in marine environments.

The life cycle involves marine mammals as definitive hosts, where the parasites mature and reproduce. Eggs released in feces hatch into free larvae, which are consumed by crustaceans (first intermediate hosts). Fish or squid ingest infected crustaceans, and the larvae migrate into the flesh as third-stage larvae (L3), which are infectious to other animals. Humans become incidental hosts by eating raw or undercooked fish or squid containing L3 larvae. In humans, the larvae cannot complete their life cycle and may migrate through the gastrointestinal tract, causing anisakiasis or triggering allergic reactions.

Clinical features in humans range from acute gastrointestinal symptoms, such as severe abdominal pain, nausea, vomiting, and sometimes vomiting blood, to milder or delayed reactions. Allergic sensitization to Anisakis proteins can occur with or without parasitic infection. Diagnosis may involve endoscopic visualization and removal of larvae, histopathology, and serologic tests. Imaging can be supportive in complicated cases. Treatment typically focuses on endoscopic or surgical removal of larvae; antiparasitic drugs are not reliably effective against established anisakid infections.

Prevention centers on avoiding raw or undercooked fish and seafood or processing it to kill the larvae. This includes proper cooking and freezing of fish prior to consumption, according to applicable guidelines. Anisakis species are distributed worldwide in marine environments and are a concern particularly in regions with diets that include raw or lightly processed seafood.