Route Of Exposure

All cephalopods, including Squid, are distinguished by distinct heads, bilateral symmetry, a mantle, and arms. Squid comprise a large, diverse group of marine cephalopods with a chitinous internal shell (cuttle). The main body mass of the Squid is enclosed in the mantle, which has 2 triangular caudal swimming fins along each side. The fins, unlike in other marine organisms, are not the main source of ambulation. At the front of the mantle cavity lies the siphon, which the Squid uses for locomotion via jet propulsion. The Squid is one of the most rapidly moving of all invertebrate organisms, and compared to the docile octopods, it is aggressive.

The skin of the Squid is covered in chromatophores. These enable the Squid to change colour to blend in with its surroundings. A transparent chitinous internal shell, called the feather, serves for muscle insertion. The head end of the Squid bears 5 pairs of arms, including a pair of long tentacles for catching prey. The tentacles each contain many suckers along the edge. The mouth of the Squid is equipped with a sharp, horny beak made of chitin. This is used to kill prey and tear it into manageable pieces. Giant squid may reach 13 m in length, but the majority are no more than 60 cm long. Ink-secreting glands cloud the water to allow escape from danger.

Squid are members of the class Cephalopoda, subclass Coleoidea, superorder Decapodiformes, order Teuthida, of which there are 2 major suborders, Myopsina and Oegopsina. Two other orders of decapodiform cephalopods are also called Squid, although they are taxonomically distinct from Teuthida and differ recognisably in their gross anatomical features. They are the Bobtail squid of order Sepiolida, and the Ram's horn squid of the single-species order Spirulida. The Vampire squid, however, is more closely related to the octopuses than to any of the Squid.

Octopuses are in the order Octopoda. Octopuses are characterised by their 8 arms, usually bearing suction cups. Unlike most other cephalopods, the majority of octopuses have almost entirely soft bodies with no internal skeleton. They have neither a protective outer shell like the nautilus, nor any vestige of an internal shell or bones, like cuttlefish or Squid.

Most of the world's catch is taken in Japan. The most abundant species found in the seas around Japan is the Japanese common squid (or Pacific flying squid; Todarodes pacificus). The variety most common in the Atlantic Ocean and the Mediterranean Sea is Loligo vulgaris. Loligo edulis and Loligo opalescens are closely related species. Many other species of Squid are utilised by man, including the Red flying squid (Ommastrephes bartramii).

Squid are popular in cuisines as widely separated as Korean and Italian. In fish markets and restaurants in English-speaking countries, Squid, especially when fried, is often known as calamari, from the Greek and Italian word for these animals. Squid can be pickled, breaded and fried, or added to stews. Pre-packaged sun-dried Squid ("surume") are popular snacks in East Asia. Squid is common in sushi and sashimi. Salted Squid may be fermented for up to a month and served in small quantities as an accompaniment to white rice or alcoholic drinks. Squid ink may be utilised in food: for example, to colour spaghetti black in the traditional Italian spaghetti al nero di seppia. Squid may be used as fish bait.

Clinical Relevance

Allergen description

No allergens from Squid (Loligo edulis) have yet been fully characterised, although a tropomyonsin has been detected. The allergens appear to be present in the Squid’s body, ink and tentacles.

Potential 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 among 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-reactive allergens from Squid (L. edulis), Cuttlefish (Sepia madokai), and Octopus (Octopus luteus) have been identified and shown to be tropomyosin; 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.

Similarly, cross-reactivity has been described between the related Pacific squid and Shrimp and among Shrimp, Oyster, Cockroach, Chionomidae larvae and Caddis fly. Tropomyosin was also shown to be a major allergen between Shrimp and Arthropoda such as mites and insects.

Clinical Experience

IgE-mediated reactions

Hypersensitivity to Squid may induce symptoms of food allergy in sensitised individuals. In reports on Squid allergy, patients generally had immediate hypersensitivity reactions after eating Squid or inhaling vapours while cooking Squid. In particular, anaphylactic reactions after consumption of Squid by patients sensitised 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 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 of Squid that results in high cross-reactivity. In fact, a patient with cutaneous symptoms who was sensitised 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 food in Japan, is used in other Asian dishes, 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, the 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 allergies 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.

Allergic interstitial cystitis caused by Squid hypersensitivity has been reported.

Exposure to Squid in the work setting may result in sensitisation and occupational allergic disease. 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.