Seafood Harvested in South Africa and Agents Implicated in Adverse Reactions

Worldwide, food allergies and anaphylaxis are increasing at a faster rate than any other allergic disorders, affecting up to 4% of adults and 8% of children. Most allergic reactions to foods can be attributed to a few food groups including seafood, which form important protein sources in Africa. The move to healthier eating habits that promote seafood consumption has resulted in more frequent reporting of allergic health problems among consumers as well as processors of seafood. Increased efforts aimed at developing more specific diagnostic tests as well as effective therapies and preventive measures are dependent on the detailed characterisation of seafood allergens. Over the past decade, a number of studies of allergic disease outcomes associated with indigenous seafood species have been conducted among consumers and processors in South Africa. These studies have focused on identifying and characterising the implicated allergens using a combination of epidemiological, immunological and molecular approaches. are classified as arthropods together with spiders and insects. Not surprisingly, allergenic tropomyosins have also been identified in insects such as cockroaches, house-dust mites and locusts, having possible clinical significance because of their cross-reactivity. Furthermore, we have demonstrated for different South African crustacean species that IgE antibodybinding profiles vary among patients and that besides tropomyosin other, as yet unidentified, allergens are implicated. The group of molluscs, subdivided into the classes Bivalvia, Cephalopoda, and Gastropods (Table I) comprises over 100 000 different species, including several important seafood groups such as mussels, oysters, abalone, snails, and squid (calamari). We identified the major allergens from abalone 9 (Fig. 3) with molecular weights of 38 kDa and 49 kDa (Hal m 1), suggesting tropomyosin as being one of these allergens (Fig. 4). Using immunoblot analysis, patients sensitised to abalone also demonstrated the complexity of immunological reactions to other mollusc species as well as to house-dust mite (Fig. 5). Among consumers the consumption of raw or insufficiently processed seafood poses probably the greatest risk to human health. Allergy-like symptoms, particularly after consumption of fish, are often caused by end products of bacterial activity causing so-called scombroid toxication. Fish with high concentrations of the amino acid histidine, such as yellowtail and snoek, are particularly problematic, as highlighted in our recent survey among food outlets in South Africa. Marine biotoxins, generated by algae, are found in fish as well as in mussels and abalone. These biotoxins can also cause allergy-like symptoms and are, as all true food allergens, not destroyed by cooking. In addition, contaminants such as nematode parasites (e.g. Anisakis pegreffii) have recently been reported to be allergenic among seafood-processing workers in South Africa. STUDIES OF ALLERGY TO SEAFOOD SPECIES AMONG SOUTH AFRICAN CON-