A rare case report on pediatric shellfish allergy

Shell ish are extensively consumed worldwide because of their nutritional value. In general they are good sources of low-fat protein rich in several essential vitamins and minerals as well as in the essential nutrients omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs) [1]. Shell ish belongs to “The Big 8” food groups causing allergy, which often does not outgrow during childhood. However, increase in IgE – mediated sea food allergy has been linked to shell ish. Seafoodassociated shell ish include crustaceans & molluskans [2]. These may cause mild local symptoms & lead to severe systemic anaphylactic reactions by ingestion, inhalation, or contact. Globally, the prevalence of shell ish allergy estimated to be 0.5% to 2.5% of the general population [3]. There are limited data showing the prevalence of shell ish allergy in children.


Introduction
Shell ish are extensively consumed worldwide because of their nutritional value. In general they are good sources of low-fat protein rich in several essential vitamins and minerals as well as in the essential nutrients omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFAs) [1]. Shell ish belongs to "The Big 8" food groups causing allergy, which often does not outgrow during childhood. However, increase in IgE -mediated sea food allergy has been linked to shell ish. Seafood-associated shell ish include crustaceans & molluskans [2]. These may cause mild local symptoms & lead to severe systemic anaphylactic reactions by ingestion, inhalation, or contact. Globally, the prevalence of shell ish allergy estimated to be 0.5% to 2.5% of the general population [3]. There are limited data showing the prevalence of shell ish allergy in children.
A study on US pediatric population showed 1.3% of shell ish allergy. Children were more allergic to crustacean (1.2%) than mollusks (0.5%) [4]. Tropomyosin is the major allergen.

Case description
6-year old male child, native of Singapore was admitted to the pediatric intensive care unit of a tertiary hospital with alleged history of consumption of cooked crab meat followed by both eyelid swelling. Swelling was painful, itchy & progressively increasing such that his vision was getting affected. He had no gastrointestinal (diarrhoea, vomiting, abdominal pain) symptoms/respiratory (breathing dif iculty, cough) symptoms. On examination, tachycardia & hypotension present. Systemic examination was normal ( Figure 1).
No past history of any allergies/comorbidities like bronchial asthma.
He was treated with intravenous luids, intravenous anti-histamine & intramuscular epinephrine. Baseline blood investigations were normal & total serum IgE level was high for age (200). Skin prick test denied by the parents & Oral food challenge unattempted in view of its risks. Avoidance of the offending food was counselled to parents & child was safely discharged in 24 hours.

Discussion
Shell ish and seafood are used synonymously among the general population. "Seafood" refers to those edible aquatic animals and "shell ish" refers to those with a shell or shelllike exoskeleton. Shell ish is furthur divided into two groups -crustacea and mollusks.
Shell ish toxic syndromes (shell ish poisoning) and Shell ish allergy are the broad conditions associated with a b shell ish consumption. Shell ish toxic syndromes include a wide variety of symptoms based on the amount of shell ish consumed and the concentration of toxins. This includesparalytic shell ish poisoning, neurotoxic shell ish poisoning, amnesic shell ish poisoning, diarrhetic shell ish poisoning, azaspiracids shell ish poisoning. All these poisonings maybe underdiagnosed when mild or misdiagnosed as allergy.
Presence of similar symptoms in other individuals who shared the meal, absence of prior reactions to same shell ish meal & its subsequent tolerance without symptoms should favour toxicity.
Many allergens have been identi ied in shell ishtropomyosin (main), arginine kinase, myosin light chain, sarcoplasmic binding protein. Among them, tropomyosin is the main crustacean allergen [5]. Symptoms due to allergic reaction from shell ish allergy range from mild to severe anaphylactic shock. True sensitization to shell ish speci ic allergens can be hampered due to the highly cross-reactive nature of some allergenic proteins. Tropomyosin has mainly linear IgE epitopes & is important in determining the degree of cross-reactivity among shell ish species. Therefore, skin prick testing helps to detect clinically allergic patients. Serum based IgE (total and allergen-speci ic) quanti ications are to be assessed. However, no species speci ic allergen has been identi ied so far to diagnose allergy to a speci ic crustacean/ molluskan species with the use of allergen molecules. Lastly, food challenge or double blind placebo controlled food challenge (DBPCFC) can be used to con irm clinical reactivity to crustacean & mollusk species. In view of its high risks and cost, the food challenge is not done routinely.

Conclusion
Shell ish allergy being a rare entity in childhood needs a more wholesome approach in diagnosis and treatment aspects.

Key message
1) No cure for shell ish allergy.
2) Avoidance of shell ish is an ideal way to prevent it.
3) Epinephrine autoinjector may be advised to parents in the event of accidental ingestion of shell ish.