Freezing protects against allergy to Anisakis simplex.

BACKGROUND: Allergic reactions to Anisakis simplex have been described following ingestion of fish and were thought to be possible even if seafood is frozen or well-cooked.
OBJECTIVE: This study aimed to confirm, by challenge test, that dead A. simplex larvae are not able to trigger allergic reactions in patients with proven hypersensitivity to this parasite.
METHODS: Simple-blind, placebo-controlled, oral challenge tests with frozen A. simplex larvae were performed in 12 patients who had suffered severe anaphylactic reactions after ingestion of seafood and diagnosed of A. simplex hypersensitivity by skin prick test and specific IgE. If no reaction appeared, they were told to eat frozen seafood. 63 patients who had suffered urticaria or urticaria/angioedema by demonstratred hypersensitivity to A. simplex were also advised to eat frozen seafood. All of them were reevaluated 6 months later.
RESULTS: All patients tolerated the dead larvae challenge test. After eating previously frozen seafood at least two times per week, all patients, including those who had suffered anaphylactic reactions and those who had only presented cutaneous manifestations, remained asymptomatic.
CONCLUSIONS: Anisakis simplex-allergic patients tolerate ingestion of dead larvae. It is probable that these patients can eat frozen fish and that a seafood-free diet is not necessary.