Herring Worm

• GeneralIt is the reason the law requires fish to be frozen before it is eaten raw or salted.
• If someone eats raw or undercooked fish carrying live larvae, they can bore into the wall of the stomach or intestine and cause anisakiasis, with severe abdominal pain within a few hours.
• Beyond the infection, its proteins cause allergy, and in sensitised people the reaction can occur even if the parasite is dead and the fish thoroughly cooked.
• It causes anisakiasis, contracted by eating raw or undercooked fish carrying live larvae. In Spain it is a problem best known from anchovies in vinegar.
• The larva cannot complete its cycle in a human, but it tries to bore through the wall of the stomach or intestine, causing severe pain, nausea and vomiting hours after eating.
• As well as infection, it causes allergy: some people react to its proteins even when the parasite is dead and the fish cooked.
• Prevention is thermal. Freezing the fish at minus twenty degrees for at least five days, or cooking it above sixty, kills the larvae. European law requires fish intended to be eaten raw to be frozen.
• Its presence has increased in recent decades, partly because of the recovery of cetacean populations, which are its definitive hosts.

Habitat & environment

A parasite: the digestive tract of fish, squid and cetaceans

Sources consulted: Rudolphi (1809); Autoridad Europea de Seguridad Alimentaria; Agencia Española de Seguridad Alimentaria y Nutrición