A double-blind, placebo-controlled oral challenge study with lyophilized larvae and antigen of the fish parasite, Anisakis simplex

Background: The third-stage larvae of Anisakis simplex may be a hidden sour ce of allergens in fish. The objective was to determine whether the ingesti on of lyophilized A. simplex larvae, or antigen, induces clinical symptoms in a group of A. simplex-sensitized patients. Methods: Double-blind, placebo-controlled oral challenges were conducted in 11 individuals who had experienced allergic reactions after eating fish. A nother patient had chronic urticaria unrelated to the ingestion of fish. Al l patients had positive skin tests and specific IgE determinations for A. s implex and negative skin tests to a battery of fish species. Conjunctival t ests with A. simplex extracts were conducted in all patients and in five co ntrols. The 12 patients received capsules containing either lactose or one, five, or 25 lyophilized larvae of A. simplex at 2-h intervals in a double- blind fashion. The highest single dose was 100 Larvae. ECP and tryptase lev els in serum were measured before and after the last oral challenge. Lyophi lized antigen was also given to five patients. Results: None of the 12 patients experienced a positive reaction after the ingestion of the placebo, the lyophilized larvae, or the antigen. Tryptase and ECP levels before and after challenges did not change significantly. Co njunctival provocation tests were positive in 11 out of the 12 patients and in none of the controls. Conclusions: The ingestion of 100 lyophilized A. simplex larvae, or its equ ivalent in antigen, does not induce clinical symptoms in individuals with a clinical history and laboratory findings of hypersensitivity to A. simplex The data suggest that only the ingestion of live larvae may be capable of inducing allergic manifestations.