Public Health Aspects of "Codworm" Infection: A Review

Abstract

Larvae of the nematode Phocanema decipiens (Ascaridida: Anisakidae), known as "codworm" in the vernacular, occur in the musculature of some cod and other marine fishes in both hemispheres, particularly in the temperate and polar climatic zones. The natural definitive hosts are Pinnipedia (seals, sea lions, walruses). For many years regarded incapable of surviving in man, recent reports from Japan indicate that in certain circumstances codworm larvae may temporarily invade the human gastric mucosa, producing clinical symptoms. Several nonclinical cases, in which the larval worms were expelled orally or in the feces of humans, have been reported from Canada (1), the USA (5), Greenland (1), and the U.K. (1). The source of human infections was raw, lightly marinated, or insufficiently cooked sea fish. The ability of codworm larvae to penetrate the stomach wall of other mammals has been demonstrated experimentally in rabbits, rats, dogs, and pigs. Natural infection of a dog in Hokkaido has been reported. For the human cases, information on age and sex of patients, specific source of infection, symptoms, and gross pathology are reviewed. The name applied to human infections and their diagnosis, treatment, prognosis, prevention, and public health implications are discussed. Cooking at 70 °C for 7 min or 60 °C for 10 min and freezing at −20 °C for 24 h are lethal to codworm larvae in fish flesh, thus providing reliable methods for preventing human infections. Some comparisons are made with larval Anisakis infections in man and future research needs, particularly in relation to the public health question, are discussed.