The “New Disease” Status of Human Anisakiasis and North American Cases: A Review

Abstract

The first confirmed case of human anisakiasis, i.e., infection with larval anisakine nematodes, occurred in 1955. The practice of holding fish refrigerated for relatively long periods before gibbing and curing, thus enabling larger numbers of anisakine larvae to move from the viscera into edible portions, as well as the increased popularity of raw and semi-raw fish recipes may partially explain the new awareness of human anisakiasis. However, it is probaly not a totally new disease. Presumptive cases are mentioned in the literature as early as 1867. Other cases may have been misdiagnosed because anisakine larvae resemble ascarid larvae in general morphology. To date, Japan (“several hundred cases”) and the Netherlands (about 160 cases) have reported the largest number of human infections. Six confirmed cases have been reported from North America. Human infections are acquired from consumption of raw, underheated, insufficiently frozen or lightly marinated fish dishes. The contained anisakine larvae (presumably belonging to genera such as Anisakis, Phocanema, Porrocaecum, and Contracaecum whose final hosts are mammals or birds) do not mature in humans but can survive long enough to cause pathology. Anisakine larvae remaining free or attached in the human digestive tract may cause irritation, severe inflammation, and ulceration; sometimes the larvae are expelled by coughing or vomiting. Anisakine larvae that penetrate totally into the tissues may stimulate a granuloma formation that surrounds and is thought to kill them. The world incidence of human anisakiasis is just being discovered. Surveys, improved criteria and methods for identifying larval anisakines, and establishment of experimental hosts and culture systems that are practical in the laboratory are needed to determine the extent of infected seafood and to prevent, diagnose correctly, and treat human infections.