Infection of humans with the nematode worm parasite Anisakis simplex was first described in the 1960s in association with the consumption of raw or undercooked fish. During the 1990s it was realized that even the ingestion of dead worms in food fish can cause severe
hypersensitivity reactions, that these may be more prevalent than
infection itself, and that this outcome could be associated with food preparations previously considered safe. Not only may allergic symptoms arise from
infection by the parasites ("gastroallergic
anisakiasis"), but true
anaphylactic reactions can also occur following exposure to
allergens from dead worms by food-borne, airborne, or skin contact routes. This review discusses A. simplex pathogenesis in humans, covering immune
hypersensitivity reactions both in the context of a living
infection and in terms of exposure to its
allergens by other routes. Over the last 20 years, several studies have concentrated on A. simplex
antigen characterization and innate as well as adaptive immune response to this parasite. Molecular characterization of Anisakis
allergens and isolation of their encoding cDNAs is now an active field of research that should provide improved diagnostic tools in addition to tools with which to enhance our understanding of pathogenesis and controversial aspects of A. simplex
allergy. We also discuss the potential relevance of parasite products such as
allergens,
proteinases, and
proteinase inhibitors and the activation of basophils, eosinophils, and mast cells in the induction of A. simplex-related immune
hypersensitivity states induced by exposure to the parasite, dead or alive.