D1.45 - Selective Anaphylaxis to Salmonids with Tolerance to Other Fish

Fish allergy is usually caused by parvalbumins, small heat-stable calcium-binding proteins that explain the wide cross-reactivity between fish species. However, some patients are sensitized to other muscle proteins, such as aldolase and enolase. This clinical variability makes diagnosis difficult and may lead to underdiagnosis of selective fish-induced anaphylaxis. We describe a patient with severe reactions to salmonids (salmon and trout) but full tolerance to other fish species.

A 66-year-old man experienced two immediate anaphylactic reactions after eating salmon and trout. He regularly tolerated cod, sardine, and tuna. He had no other allergic diseases. Skin prick tests with commercial extracts were performed. Serum IgE levels were measured by ISAC. Also, raw and cooked protein extracts from salmon and trout were prepared following validated protocols. SDS-PAGE and IgE Western blot were performed under reducing and non-reducing conditions using the patient’s serum to identify IgE-binding proteins. Moreover, oral food challenge was realised. 

Skin tests with commercial fish extracts were positive for salmon and trout and negative for fish, cod, flounder, tuna, and swordfish. Skin tests with raw and cooked salmon were also positive. Specific IgE for salmon was positive (0.56 kUA/L) and trout ( 0.59 kUA/L) and negative for the all others. Also, sIgE for Gad c 1 and Cyp c 1 Parvalbumina were negative (<0.3 ISU-E). Western blot revealed a band of approximately 35 kDa in all extracts, compatible with tropomyosin (Sal s 4). In raw trout, several IgE-binding proteins between 40 and 100 kDa were observed, likely corresponding to aldolase and enolase; these bands disappeared after cooking, indicating heat sensitivity. A band around 12 kDa, compatible with parvalbumin (Sal s 1), was detected only under reducing conditions in cooked salmon and trout, suggesting that heating increased epitope exposure.

This case shows selective anaphylaxis to salmonids caused by a combination of heat-stable and heat-labile fish allergens. Standard diagnostic tests were insufficient, while IgE Western blot allowed identification of the relevant proteins. Detailed molecular analysis was essential to explain the species-specific reactions and to provide safe dietary advice, highlighting the value of advanced diagnostic approaches in selective fish allergy.