Cod
Summary
Cod (family Gadidae) is an economically important fish distributed in the northwest Atlantic Ocean found in Canadian waters, Greenland, and North Carolina. It is a cold-water fish, which can survive in nearly freezing to 20oC temperature and found in both fresh and marine water. Cod protein content is usually between 15-20% of their body weight. In codfish, the major allergen is the muscle protein parvalbumin, which is a calcium-binding protein. Parvalbumin is also known as “Gad c 1”, and it is the first calcium-binding allergen characterized from codfish, which cannot be destroyed by heat or cooking. Hence, if the individual or sensitized person is exposed to the cod allergen through oral, nasal or occupational route, the allergen triggers an allergic reaction. Detection of codfish allergy is based on clinical history, skin prick test, and specific IgE and immunoblotting tests.
The codfish cross reactivity was closely related to mackerel (Perciformes), herring (Clupeiformes), and plaice (Pleuronectiformes). Also, cods parvalbumins (Gad c 1) cross react with parvalbumins from salmon (Sal s 1), and pollack (The c 1).
Epidemiology
Worldwide distribution
Prevalence rates of fish allergy are 0.7 % in the global population. Higher prevalence was observed in the pediatric groups and in long coastline countries with fish as a staple food and fish-processing industries. A cross-sectional, random telephonic national survey conducted in the USA reported 3.3% of the general population has a seafood allergy.
Route Of Exposure
Main
The route of exposure is mainly an oral route through consumption, but touch and inhalation of fish and related products can as well trigger allergic reactions.
Clinical Relevance
In cod allergic patients, incomplete digestion of cod can lead to anaphylaxis. While in non-allergic subjects, fish allergens are identified within 10 min and reach a peak in 1-2 hrs. after ingestion. Digestive enzymes cause protein fragmentation, which reduces biological activity. However, increasing pH to 3.0 for digestion leads to reactivity patterns comparable to undigested extracts.
Codfish allergy symptoms can affect single or multiple organs, ranging from mild to severe anaphylaxis. Clinical symptoms start in less than 1 min after fish exposure. This can lead to cutaneous (urticaria, angioedema), GI (oral allergy syndrome, laryngeal edema, spasm, diarrhea, vomiting), and respiratory (rhino-conjunctivitis, bronchospasm) and severe anaphylaxis in some cases.
Diagnostics
Detection of allergy is based on clinical history, skin prick test, specific IgE tests, histamine release test, and immunoblotting, followed by oral fish challenge. Serum IgE antibodies levels are estimated along with the clinical reactivity to predict fish allergy.
Prevention And Therapy
Prevention strategies
Avoidance
Fish allergic individuals should strictly avoid fish in any form including fish-derived products.
Cross-Reactivity
A study by Hensen in 1997, showed that all clinically codfish-sensitive adults have serological cross-reactivity to other fish species.
The parvalbumins from salmon (Sal s 1), pollack (The c 1) showed high identity indices with the amino acid sequence of cod (Gad c 1), which supports the cross-reactivity between these fish species. The identity indices of Gad c 1 amino acid sequence were similar to parvalbumins from Sal s 1 (68%) and the c 1 (62%), which highlights the cross-reactivity.
References
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- Gadusmorhua. Integrated Taxonomic Information System (ITIS) 2020.
- FAO. The Composition of Fish 2020 [2020-10-15]. Available from: http://www.fao.org/3/x5916e01.htm#Introduction.
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- Hansen TK, Bindslev-Jensen C, Skov PS, Poulsen LK. Codfish allergy in adults: IgE cross-reactivity among fish species. Ann Allergy Asthma Immunol. 1997;78(2):187-94.
- Untersmayr E, Vestergaard H, Malling HJ, Jensen LB, Platzer MH, Boltz-Nitulescu G, et al. Incomplete digestion of codfish represents a risk factor for anaphylaxis in patients with allergy. J Allergy Clin Immunol. 2007;119(3):711-7.
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- Van Do T, Elsayed S, Florvaag E, Hordvik I, Endresen C. Allergy to fish parvalbumins: studies on the cross-reactivity of allergens from 9 commonly consumed fish. J Allergy Clin Immunol. 2005;116(6):1314-20.