All over the world, fish and shellfish play a significant role in human nutrition and are utterly popular in some parts of the world. The intense move to healthier  eating habits and the replacement of meat with seafood in the diet has led to in even greater demands for fish and shellfish. On the other hand, seafood may also be powerful allergens in sensitized individuals and cause unfavorable reactions.
There are over 2000 species of fish, more than 5000 species of molluscs and 2500 species of crustaceans in Southern Africa. The major edible seafoods that can cause an allergic reaction belong to three groups: 1) Mollusca: 2) Arthropoda; and 3) Chordata. The Mollusc group includes three different classes of seafood with delicious species such as Abalone (Perlemoen), oysters, mussels, and squid (Calamari).
The second group, the Crustacea, includes the rock lobsters (“crayfish”), prawns, crabs and shrimps. The third important group of seafood includes all the common edible fish, such as Hake, Cod, Snoek, and so on. As a rule, patients are only allergic to certain species but are able to eat other seafood species without any problem.
Nevertheless, the examination of a patient can be difficult if the inimical reaction to certain seafood was  caused by a non-allergic reaction. The main cause is the occurrence of a toxin in fish and shellfish, which provoke symptoms analogous to allergic reactions. Among fish species such as Yellowtail, Tuna and Mackerel, scombroid fish poisoning is frequently happened if the fish is inappropriately refrigerated or when refrigeration is postponed. In filter-feeding shellfish such as black mussels and oysters, toxins produced by “Red Tide” along the West Coast are found, mostly in later summer. Recently allergic reactions to a parasitic worm, Anisakis, which is often found in a variety of fish species, has been described in people eating fish, and can imitate a fish sensitivity.
Seafood Allergy in South Africa
At present there is no strict data available as to how common seafood allergy is in South Africa. Depending on regional diets, certain seafoods are more allergenic than others. For instance, shrimp allergy is widespread in the southern USA while fish allergy is common in Spain and the Scandinavian countries, striking up to 1:1000 individuals. Moreover, international studies have confirmed that occupational asthma or eczema can effect up to 30% of individuals in different seafood-processing industries. A recent study conducted in South Africa by the UCT Allergology Unit indicates that allergy to different mollusc and crustacea species is far more common that allergy to fish.
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