Clinical Relevance

IgE-mediated reactions

Hypersensitivity to Squid may induce symptoms of food allergy in sensitized individuals. In reports on Squid allergy, patients generally had immediate hypersensitivity reactions after eating Squid or inhaling vapors while cooking Squid. In particular, anaphylactic reactions after consumption of Squid by patients sensitized to House dust mites have been reported several times. Serum-specific IgE to Squid has been measured in patients with atopic dermatitis (but the clinical significance was not determined by challenges).

A difficulty in assessing the early reports of hypersensitivity to Squid is that the species involved were not identified. The assumption can be inferred but not absolutely confirmed that the species are closely interrelated and that tropomyosin is a major allergen in Squid that results in high cross-reactivity. In fact, a patient with cutaneous symptoms who was sensitized to Loligo opalescens and not to Loligo pealei has been described.

Hypersensitivity to Squid may occur more commonly than indicated in the literature, considering that Squid is an important seafood in Japan, is used in other Asian cuisine, and in recent times is commonly served in restaurants. Shellfish – and especially Cephalopoedae (Octopus, Squid) – is one of the most popular foods in Spain. Shellfish is one of the most frequent causes of food hypersensitivity in this population and is the leading cause of food hypersensitivity in patients over 5 years of age.

In 48 Spanish adults with crustacea allergy, the most frequent causes of symptoms were Shrimp (33 cases) and Squid (24 cases); the most frequently found symptoms were urticaria/angioedema (39 patients), asthma (18 patients), and rhinitis (14 patients). The authors suggested that shellfish hypersensitivity can occur within the same phylum and between different phyla, reflecting common epitopes, and that Squid, Octopus, and Limpet extracts contain large amounts of heat-stable allergens. There was no significant difference between prick tests with raw and with cooked extract.

Among 142 adult patients sensitised to foods (out of 7698 patients visiting an outpatient clinic in the Canary Islands), 120 experienced clinical symptoms after consumption of 1 or more foods. Sensitisation to Squid was reported in 33 patients.

In 7 patients who had had symptoms highly suggestive of IgE-mediated reactions after ingesting Squid or inhaling vapours from cooking Squid, symptoms reported were nasopharyngeal pruritus, rhinoconjunctivitis, asthma, nausea, vomiting or diarrhoea, and urticaria and angioedema. All had previously suffered from persistent rhinitis or asthma for years as a result of allergy to mites. In addition, 6 of the 7 patients had had symptoms after ingesting Shrimp. Skin-specific IgE tests were strongly positive for boiled Squid extract and for various commercial crustacean extracts. Only 2 had borderline responses to the raw Squid extract. Specific IgE antibodies against boiled extract and several crustacean extracts were demonstrated in all patients.

Anaphylactic reactions after consumption of Squid by patients sensitised to House dust mites have been reported several times. A 5-year-old boy allergic to House dust mites developed an angioneurotic oedema after eating Squid. Skin and serum-specific IgE showed an allergy associated with both House dust mites and Squid. The labial test was strongly positive, with labial oedema, swelling and intense itching. The author suggested that in light of the potential seriousness of anaphylactic reactions, parents of children allergic to House dust mites, along with the children themselves, should be made aware of the increased risk of allergy to Squid

Possible exercise-induced anaphylaxis after eating both Shrimp and Squid was reported in a 13-year-old Japanese boy who was sensitised to Shrimp, Squid, Crab, Octopus, Clam, and Short-neck clam.

Occupational protein contact dermatitis was described in a 24-year-old female fishmonger who presented with progressive episodes of dermatitis of the hands and forearms for 2 months. Symptoms were associated with cleaning baby Squid, which resulted a few minutes after starting with itching and erythema of the anterior forearms, followed 2 days later with vesicles and maculopapular lesions. Skin-specific IgE tests with seafood other than cephalopods were negative. Skin-specific IgE with baby Squid (Loligo vulgaris) was positive, but negative to adult Squid of the same species, Pacific squid (Toradodes pacificus), and Octopus (Octopus vulgaris). Patch test was positive to baby Squid.

Contact urticaria from L. japonica was reported by a 22-year-old male cook. Every time he handled uncooked Squid, he developed erythema, oedema, and itching and burning on his hands. Symptoms started within 15 to 20 minutes of contact. An open challenge of fresh Squid applied to his forearm provoked a reaction within minutes. Serum- and skin-specific IgE directed to L. japonica was established.

Occupational allergic contact dermatitis from Squid (L. opalescens) was reported in an 18-year-old female, who developed eczema on her hands and forearms a month after starting work on cleaning frozen Squid. Her symptoms worsened during the week and improved on weekends. An open patch test was negative, but a closed patch test was positive at 2 and 4 days to L. opalescens, though not to L. pealei. Patch tests with the body, ink and tentacles of L. opalescens were positive at 2 and 4 days

Other reactions

It may be useful to evaluate anglers for sensitisation to Squid, if they are found to be allergic to bait. This is suggested by a report on a keen angler, who used maggots as bait on weekends and suffered with rhinoconjunctivitis for years. He was found to be allergic to maggots and also sensitised to Squid and, to a lesser extent, to Prawns

Cross-Reactivity

Cross-reactivity between species of Squid could be expected but does not necessarily occur, even given the close interrelatedness of species. For example, a patient with cutaneous symptoms was sensitised to L. opalescens but not to L. Pealei.

In 7 patients who had had symptoms highly suggestive of IgE-mediated reactions after ingesting Squid or inhaling vapours from cooking Squid, cross-reactivity among Squid and Shrimp and other crustaceans (Lobster, Crab) was demonstrated, but none between Squid and Octopus, both cephalopods, nor between Squid and other mollusks (Round clam and Mussel; only Oyster extract produced nearly 50% inhibition).

Where cross-reactivity has been reported, this has been attributed to the presence of the panallergen tropomyosin rather than to familial relatedness. For example, cross-reactivity has been described between Pacific squid and Shrimp, and among Shrimp, Oyster, Cockroach, Chionomidae larvae and Caddis flies. Tropomyosin was also shown to be a major allergen connecting Shrimp and arthropods such as mites and insects.

Similarly, cross-reactive allergens from Squid (L. edulis), Cuttlefish (Sepia madokai), and Octopus (Octopus luteus) have been identified and shown to be tropomyosins; and as tropomyosin is conserved among invertebrates, cross-reactivity may occur to inhaled or ingested insects. Allergenic tropomyosins are found in invertebrates such as crustaceans (Shrimp, Lobster, Crab, Crawfish), arachnids (House dust mites), and insects (Cockroaches). Vertebrate tropomyosins are nonallergenic. Furthermore, immunological relationships among crustaceans, Cockroaches and House dust mites have been established and suggest that tropomyosin is an important cross-sensitising panallergen.

In a study of 35 shellfish-allergic patients, no significant difference between raw and boiled Squid or Octopus was found. Of Squid-positive patients, 73.7% also reacted to Cockroach. There was a strong association of skin-specific IgE among Shrimp, Squid, Lobster and Crab in 18 patients. Furthermore, the deduced amino acid sequences of Pan s I (Spiny lobster) and Hom a I (American lobster) show significant homology to Shrimp tropomyosin.