Grass carp a major source of fish allergy in HK

Grass carp may be the major source of fish allergy in Hong Kong, with Cten i 1 identified as a new allergenic marker and the main contributor to high immunoglobulin E (IgE) reactivity in a recent study by researchers from the Chinese University of Hong Kong (CUHK).

“Most of the standard fish allergy tests nowadays are based on fish models from the West, such as salmon and cod. As Chinese dietary habits are distinct, more fish species, such as freshwater fish, should be included in allergy tests to provide a comprehensive profile for accurate diagnosis and promote appropriate food avoidance,” said Professor Ting-Fan Leung of the Department of Paediatrics, CUHK.

In a double-blind, placebo-controlled food challenge study, 28 patients (average age, 6.9 years; male, 64.3 percent) with a history of immediate allergic reactions ≤2 hours of fish consumption or contact on ≥2 exposures in the past 2 years were offered oral titrated challenges with grass carp, salmon and placebo on 3 separate days in a randomized order, each at least 48 hours apart. [J Allergy Clin Immunol Pract 2020;8:2098-2100.e8]

Results showed that 71 percent (n=20) were challenge-positive to either grass carp or salmon (n=1) or both (n=5), whereas 29 percent (n=8) were challenge-negative to both. Median doses which led to an allergic reaction were significantly lower with grass carp than salmon (lowest observed adverse effect levels [LOAELs], 10 g vs 52.8 g; p=0.021).

“Results of our study showed that grass carp was the major source of fish allergy among our study cohort, and partial tolerance to selected fish species is common in Chinese fish-allergic patients,” said Dr Agnes Leung of the Department of Paediatrics, CUHK.

“The sensitivity of serum IgE [sIgE] measurement of fish allergens based on commercially available diagnostic instruments was only 73.7 percent for cod extract, but 100 percent for grass carp, potentially resulting in cases being undiagnosed due to false negative results. The choice of fish allergens for specific IgE measurements should thus be tailored to individual fish-allergic patients,” she suggested.

Results of an immunology characterization study in 69 patients with history of IgE-mediated allergic reaction to grass carp showed higher allergenicity of grass carp parvalbumin than cod and salmon (specific IgE level, 4.85 kU_A/L vs 1.75 kU_A/L vs 1.34 kU_A/L), despite sharing high sequence homology. [Pediatr Allergy Immunol 2020;31:792-804]

Parvalbumin isoform Cten i 1 was identified with the highest IgE reactivity compared with Gad m1, Sal s 1 and Cyp c 1 following purification. Based on these results, Cten i 1 has been registered in the WHO and International Union of Immunological Societies allergen database.

“Based on this groundbreaking finding, our team is now working on allergy tests based on IgE or basophil activation level. We encourage members of the public to participate in our studies to provide a comprehensive profile of sources of food allergy in Hong Kong,” said Professor Leung.