Contact urticaria caused by heat-sensitive raw fish allergens

Patients allergic to fish usually present with skin reactions after handling raw fish. Less frequently, these reactions are seen without symptoms after oral intake, often in chefs and food handlers. We have attempted to explain the skin selectivity of such reactions in a 36-year-old woman with contact urticaria after handling raw fish. We obtained aqueous extracts of raw and cooked fish (sole and hake) for in vivo (prick test) and in vitro (SDS-PAGE, IgE Immunoblot) tests. Prick-by-prick test, 20-min closed patch test, rub test with fresh and cooked fish (sole, hake and cod) and specific IgE (CAP-system) to sole, cod and hake were performed. The strength of positive reaction to raw fish was greater than to cooked fish on both prick and prick-by-prick testing. Rub tests showed positive responses only to raw fish. Specific IgEs to sole (45 KU/l), hake (66.9 KU/l) and cod (18.7 KU/l) were obtained. IgE immunoblot recognized 3 antigens of 25, 48, 56 kDa in raw sole and 1 of 42 kDa in raw hake extracts. No IgE binding was observed with the cooked extracts or control sera. Our findings strongly suggest a Type-I hypersensitivity to fish. Immunoblot analyses demonstrated a loss of specific IgE binding to cooked extracts. We have reported a case of contact urticaria caused by heat-sensitive raw-fish allergens in a patient who probably became sensitized via the cutaneous route.