Anisakiasis is a zoonotic nematode infection that causes acute and chronic gastrointestinal granulomatous disease in humans. For most patients, the causative agents are larvae of nematodes of the genera Anisakis and Pseudoterranova, and the source of infection is marine fish or squids harboring these larvae (1). Within 8–12 hours after infected fish are ingested, the larvae penetrate into the person’s stomach or intestinal wall, causing acute abdominal pain, indigestion, nausea, and vomiting; pathologic findings are edema, hyperemia, and bleeding in the surrounding mucosa (1,2). The diagnosis is usually based on morphologic identification of the larvae or on histopathologic identification of sectioned larvae (1). However, molecular techniques have recently been developed as effective tools not only for the diagnosis of individual cases but also for studies of taxonomy and evolution of anisakid nematodes (3,4).
Anisakiasis in humans was first reported in the Netherlands; since then, it has been reported extensively in Japan (≈2,000 cases annually), South Korea (≈200 cases annually), and some European countries (≈500 cases annually) where people eat raw or undercooked fish (1,2). In the United States, up to 50 human cases are reported each year (1). Most infections in humans have been caused by Anisakis simplex sensu stricto and Pseudoterranova decipiens nematodes (1); however, since 1999, a few human infections with Anisakis pegreffii larvae (a sibling species of A. simplex s.s.), originally recovered from a Mediterranean monk seal (5), have been reported in Italy (6–9) and Japan (10,11). The larvae of A. pegreffii are morphologically distinguished, with difficulty, from those of A. simplex s.s. (both are Anisakis type I); however, molecular techniques can easily distinguish the 2 types of larvae (3,4).
In South Korea, Anisakis type I larvae recovered from humans and fish have been assigned to A. simplex s.s., on the basis of morphologic appearance (1,12). We performed molecular analyses of 26 Anisakis type I larvae recovered from 16 humans in South Korea by using DNA sequencing of the nuclear internal transcribed spacer (ITS) genes.