Review of the regulatory management of food allergens

5.2 Collective term: ‘fish’

The current list of substances subject to mandatory declaration requirements (clause 4 of Standard 1.2.3 – Mandatory declaration of certain substances in food) includes fish and crustacea. The term ‘fish’ is defined in the Code⁴ to mean aquatic vertebrates and invertebrates including shellfish. Based on this definition, the term fish in Standard 1.2.3 is interpreted to include finfish and shellfish (i.e. crustaceans and molluscs). However, Standard 1.2.3 is inconsistent in that it requires crustacea to be declared separately from fish, but does not specify the declaration of molluscs. Also, clause 4 of Standard 1.2.4 sets out the conditions for the use of generic names including ‘fish’ requiring crustacea to be declared by their specific name in the list of ingredients, but does not have specific provisions for finfish or molluscs. Consumer and industry stakeholders have raised concerns with FSANZ regarding the inconsistency and lack of clarity in relation to the declaration of molluscs.

The purpose of allergen declaration is to alert allergic consumers to the presence of food or food groups which they need to avoid. The term ‘fish’ as defined in the Code includes the three main groups of aquatic animals commonly consumed as food, i.e, finfish, crustacea and molluscs. These three food groups are also collectively referred to as ‘seafood’⁵. In the context of allergen declaration, such generic terms do not provide adequate information to allergic consumers to identify the specific food or food group of concern to them. This is particularly the case for food groups which represent different allergens; i.e., where there are likely to be consumers who need to avoid one food group (such as crustaceans or molluscs), but not another (such as finfish). Therefore, the relevant information to consider is whether finfish, crustaceans and molluscs represent allergenically distinct groups.
Seafood is an important source of human nutrition in many countries around the world. The three main groups in this food category, i.e. finfish, crustacea and molluscs, cause severe allergic reactions, including anaphylaxis. Most information on the prevalence and incidence of severe reactions to seafood is based on studies on patient materials and selected groups (Sampson, 2000; Sicherer et al., 2004;Taylor, 2008). Only a few population-based epidemiological studies are available in the literature. Two such studies from the USA estimated the prevalence of seafood allergy in adults to be between1.3% and 2.8% (Sicherer et al., 2004; Vierk et al. 2007).
The term ‘shellfish’ is commonly used to refer to a diverse group of species of crustaceans and/ or molluscs representing the two Phyla – Arthropoda and Mollusca. Crustaceans, a Class within Arthropoda, include prawn, crab, lobster, crayfish and barnacles. The Mollusca Phylum includes abalone, oyster, mussel, scallop, squid and octopus.
Shellfish allergy is an important cause of food induced anaphylaxis around the world for both children and adults (Kandyil and Davis, 2009). Studies from Europe and the USA estimate that shellfish allergy affects around 2% of the population, four times higher than the estimated prevalence of allergy to finfish (Rona et al. 2007, Sicherer et al., 2004, Vierk et al. 2007). Ben-Shoshan et al., 2010) reported that the prevalence of physician-confirmed shellfish allergy to be 0.73% in the Canadian population. In Australia, 5.9% of households participating in an internet survey perceived that at least one family member has shellfish allergy (Allen et al., 2009).
The following is a summary of the scientific and clinical information available on the allergenicity and cross-reactivity of finfish, crustaceans and molluscs.

5.2.1 Allergy to finfish

Allergy to finfish is estimated to affect 0.4% of the USA population (Sicherer et al., 2004; Vierk et al. 2007). A similar estimate was reported in the European population (Rona et al., 2007). In Canada, the prevalence of physician-confirmed fish allergy was reported to be 0.1% (Ben-Shoshan et al., 2010). Based on an internet questionnaire, the prevalence of self-reported perceived allergy to fish in Australia was 2.5% of households surveyed (Allen et al., 2009).

The majority of fish-allergic individuals are sensitised to parvalbumins, a subfamily of closely related 12 kDa calcium-binding proteins present in high amounts in the white muscles of fish and other lower vertebrates. There is a high degree of sequence homology of the parvalbumins in multiple fish species, which probably accounts for most of the clinical cross-reactivity seen in fish allergic patients (Helbling et al., 1999; Poulsen et al., 2001; Swoboda et al., 2002; Van Do, 2005). Up to 50 % of individuals allergic to one species of fish are at risk for reacting to a second species (Sicherer, 2001; Torres Borrego, 2003).
Parvalbumin, however, was not involved in a clinical case of cross-reactivity between tuna and marlin reported by Kondo et al. (2006); and species-specific allergens have been reported (Yamada et al., 1999; Rosmilah et al., 2005). Recently published studies suggest that variations in the expression levels of parvalbumin in different fish species may determine their allergenicity (Griesmeier et al., 2009; Kuehn et al., 2010).
The major fish allergen parvalbumin is resistant to boiling and to enzymes of the gastrointestinal tract (Elsayed and Asa,1971). A number of other fish allergens are temperature sensitive which may explain why cooked or canned fish can be tolerated by some allergic consumers (Yamada et al., 1999). Cross-reactivity between fish and shellfish has not been reported.

5.2.2 Allergy to crustaceans

More than 30,000 species of crustaceans have been identified, but only a few are commonly consumed as food including prawn, lobster, and crab. Crustaceans are reported in the medical literature to be the most common seafood allergen (Lopata and Jeebhay, 2001; Zhang et al., 2006). In a multi-centre study of the causes of food-induced anaphylaxis in Italian adults, the second most common anaphylactic episodes occurred in patients sensitised to shrimp.

The major allergen in crustaceans has been identified as the 34 kDa muscle protein tropomyosin (Daul et al., 1991; Shanti et al., 1993; Leung et al., 1994; Motoyama et al., 2007). Tropomyosin sequence homology and serological cross reactivity between crustaceans has been reported (Leung et al., 1998a; Leung et al., 1998b; Leung and Chu, 1998).

Cross-reactivity between a number of crustacean species including prawn, lobster, crayfish and crab is documented (Ayuso et al., 2002, Zhang et al., 2006). Evidence suggests that allergy to one species of crustacean presents a 75% risk of allergic reaction to another species (Sicherer, 2001; Torres-Borrego, 2003).

Closely related tropomyosins have also been identified in molluscs (Miyazawa et al., 1996; Ishikawa et al., 1998). Interestingly, tropomyosin has also been identified as an important allergen in other invertebrates including dust mites and cockroaches. Many shellfish-allergic children have sensitivity to dust mite and cockroach allergens (Ayuso et al., 2002; Kandyil, 2009).
In addition to tropomyosin, two new shrimp proteins, arginine kinase and myosin light chain were recognised by IgE in serum from shrimp-allergic individuals (Yu et al., 2003; García-Orozco et al., 2007; Ayuso et al., 2008). More recently, Ayuso et al., (2009; 2010) identified a sarcoplasmic calcium-binding protein which appears to be of particular importance in the paediatric population.

5.2.3 Allergy to molluscs

The Phylum Mollusca is classified into eight Classes, of which 3 are important as food. These are: Gastropods, e.g. abalone, land and marine snails; Bivalves, e.g. oyster, mussel, scallop, clam; and Cephalopods, e.g. squid, octopus, cuttlefish.

While shellfish allergy is well documented in the medical literature, it is often difficult to ascertain whether molluscs and/or crustaceans are involved. A few cases of allergic reactions to molluscs have been reported from clinics in European countries and Japan (EFSA, 2006; Taylor 2008). Reactions, including anaphylaxis, were reported to abalone, limpet, clam, cockle, oyster, mussel, scallop, snail, squid and cuttlefish (Thong et al., 2005; González Galán et al., 2002; Pastorello et al., 2001; EFSA, 2006; Taylor 2008).
The protein tropomyosin has been identified as the major allergen in many molluscan species (Miyazawa et al., 1996; Leung et al.,1996; Chu et al., 2000; Leung and Chu., 2001). In vitro cross-reactivity with IgE antibodies from patient sera have been reported (Leung and Chu, 1998; Leung et al., 1996; Motoyama et al., 2006; Reese et al., 1999). Within the entire mollusc group, tropomyosin sequence identity is between 68% to 100% (Taylor, 2008). Clinical cross-reactivities between molluscan species have been reported, but appear to be fairly uncommon.
As noted in the previous section, tropomyosin is also the major allergen in crustaceans. Tropomyosin from crustacean species and molluscan species share protein sequence identity of 56-68% (Taylor, 2008). Tropomyosin sequence homology is believed to be responsible for clinical cross reactivity between crustaceans and molluscs, as well as non-food allergens such as dust mites (Lopata et al., 2010).
In addition to tropomyosin, a number of proteins have also been identified as putative allergens in molluscs (Taylor, 2008). However, the role of these proteins in allergy to molluscs, possibly as species-specific allergens, is not fully understood.

5.2.4 Conclusions

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  Finfish, crustaceans and molluscs are taxonomically distinct groups widely consumed around the world. Clinical allergic reactions to finfish, crustacean and molluscan species have been reported from a number of countries, mainly in Europe, North America and South Asia.
  

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  The major allergenic proteins in finfish been identified as parvalbumin. Clinical cross-reactivity to multiple fish, in individuals with fish allergy based on the major fish allergen parvalbumin, is commonly observed.
  

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  The major allergenic protein in crustaceans and molluscs is tropomyosin. There is no cross-reactivity between finfish and either molluscs or crustaceans; i.e. individuals with allergy to finfish only, are able to consume mollluscs and crustaceans and vice versa. Tropomyosin sequence homologies are found in the commonly edible crustaceans and molluscs, however evidence of clinical cross-reactivity between these two groups is limited.
  

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  Molluscs and crustaceans are allergenically distinct from finfish. Therefore, the terms ‘fish’ and ‘seafood’ as defined in the Code, are not useful in the context of allergy to finfish, crustaceans and molluscs. Terms that allow consumers to identify the specific group would be more compatible with the intent and purpose of allergen declaration requirements.
  

5.2.5 Recommendation

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  FSANZ to consider this issue further in consultation with the relevant stakeholders in Australia and New Zealand. In particular, information from the food industry and food service sector in relation to current practices and commonly used terms, would assist in developing options to improve the clarity of the mandatory declaration requirements.