Thank you for your inquiry.
The first question is easier to answer than the second. You are correct that tropomyosin is the major allergen in shrimp and in prawn as well. However, the situation is not as simple as that. As you can see from the abstracts copied below, there are other allergens in prawn that may not be present in all shrimp. And, even though tropomyosin is relatively well preserved, there are clearly different species of tropomyosin. Thus, it is not uncommon to see patients who may react to one species of crustacean and not another even though tropomyosin is a common allergen in many. If you would like to read further about this, the full article by Woo and Bhana is available to you free of charge online. You can access it by copying and pasting the link below in your web browser.
Unfortunately I have no ready explanation for your second question. Although the lay literature does contain references to delayed reactions to shrimp (as well as other foods), I could find nothing on a search of the scientific literature citing a reference to this. For your interest, however, here is a link to a lay website that discusses patients' observations of delayed reactions to shrimp, listing it as "one of the top 20 foods to which delayed reactions occur." But, as noted, I have no explanation for this phenomenon and could find no reference to it in the scientific literature. Therefore any explanation I could offer you would only be conjecture.
Thank you again for your inquiry and we hope this response is helpful to you.
Not all shellfish “allergy” is allergy!
Chee K Woo and Sami L Bahna*
Clinical and Translational Allergy 2011, 1:3
The popularity of shellfish has been increasing worldwide, with a consequent increase in adverse reactions that can be allergic or toxic. The approximate prevalence of shellfish allergy is estimated at 0.5-2.5% of the general population, depending on degree of consumption by age and geographic regions. The manifestations of shellfish allergy vary widely, but it tends to be more severe than most other food allergens.
Tropomyosin is the major allergen and is responsible for cross-reactivity between members of the shellfish family, particularly among the crustacea. Newly described allergens and subtle differences in the structures of tropomyosin between different species of shellfish could account for the discrepancy between in vitro cross-antigenicity and clinical cross-allergenicity. The diagnosis requires a thorough medical history supported by skin testing or measurement of specific IgE level, and confirmed by appropriate oral challenge testing unless the reaction was life-threatening.
Management of shellfish allergy is basically strict elimination, which in highly allergic subjects may include avoidance of touching or smelling and the availability of self-administered epinephrine. Specific immunotherapy is not currently available and requires the development of safe and effective protocols.
Malays J Med Sci. 2011 Jul-Sep; 18(3): 27–32.
Identification of Major and Minor Allergens of Black Tiger Prawn (Penaeus monodon) and King Prawn (Penaeus latisulcatus)
Background: Prawns and shrimp are a frequent cause of seafood allergy mediated by IgE antibodies. Penaeus monodon and Penaeus latisulcatus, commonly known as black tiger prawn and king prawn, respectively, are among the most frequently consumed prawns in Malaysia. The aim of this study was to identify the IgE-binding proteins of these 2 prawn species.
Methods: Raw and boiled prawn extracts were prepared and then resolved by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). IgE-immunoblotting was then performed using sera from patients with positive skin prick tests to the raw prawn extracts.
Results: SDS-PAGE analysis of the raw extracts of both prawn species revealed 23 protein bands; the boiled extracts yielded fewer protein bands. The bands in the range of 40 to 100 kDa were sensitive to heat and therefore were not found in the boiled extracts. Immunoblot of raw extracts of black tiger prawns and king prawns yielded 14 and 11 IgE-binding proteins, respectively, with molecular weights of between 15 and 200 kDa. Proteins at 36, 42, and 49 kDa were detected as the major allergens in both species of prawns. A protein of 75 kDa was also identified as a major allergen in black tiger prawns. Other potential allergens were also observed at various molecular masses.
Conclusion: Proteins of 36, 42, and 49 kDa were identified as the major allergens of both species of prawns. The 36 and 42 kDa proteins are hypothesised to be tropomyosin and arginine kinase, respectively. A high molecular weight protein of 75 kDa was found to be an additional major allergen in black tiger prawns.
Keywords: allergens, allergy and clinical immunology, hypersensitivity, Penaeus, immunoblotting, tropomyosin
Int Arch Allergy Immunol. 2008;146(2):91-8. doi: 10.1159/000113512. Epub 2008 Jan 18.
Sarcoplasmic calcium-binding protein: identification as a new allergen of the black tiger shrimp Penaeus monodon.
Shiomi K, Sato Y, Hamamoto S, Mita H, Shimakura K.
Department of Food Science and Technology, Tokyo University of Marine Science and Technology, Tokyo, Japan.
Background: Tropomyosin and arginine kinase have been identified as crustacean allergens. During purification of arginine kinase from black tiger shrimp Penaeus monodon, we found a new allergen of 20-kDa.
Methods: A 20-kDa allergen was purified from the abdominal muscle of black tiger shrimp by salting-out, anion-exchange HPLC and reverse-phase HPLC. Following digestion of the 20-kDa allergen with lysyl endopeptidase, peptide fragments were isolated by reverse-phase HPLC, and 2 of them were sequenced. The 20-kDa allergen, together with tropomyosin and arginine kinase purified from black tiger shrimp, was evaluated for IgE reactivity by ELISA. Five species of crustaceans (kuruma shrimp, American lobster, pink shrimp, king crab and snow crab) were surveyed for the 20-kDa allergen by immunoblotting.
Results: The 20-kDa allergen was purified from black tiger shrimp and identified as a sarcoplasmic calcium-binding protein (SCP) based on the determined amino acid sequences of 2 enzymatic fragments. Of 16 sera from crustacean-allergic patients, 8 and 13 reacted to SCP and tropomyosin, respectively; the reactivity to arginine kinase was weakly recognized with 10 sera. In immunoblotting, an IgE-reactive 20-kDa protein was also detected in kuruma shrimp, American lobster and pink shrimp but not in 2 species of crab. Preadsorption of the sera with black tiger shrimp SCP abolished the IgE reactivity of the 20-kDa protein, suggesting the 20-kDa protein to be an SCP.
Conclusions: SCP is a new crustacean allergen, and distribution of IgE-reactive SCP is probably limited to shrimp and crayfish.
Phil Lieberman, M.D.