Summary

Shrimp is a commercially important decapod crustacean species and is considered to be a highly allergenic food, causing severe reactions, such as anaphylaxis. The shrimp allergen is present in its abdominal and tail muscle regions. Asians are reported to have higher prevalence of shellfish allergy compared to Western countries. Moreover, children are found to have a lower incidence of shellfish allergy than adults. Shrimp allergy is primarily caused due to consumption of shrimp meat and secondarily due to handling of shrimp, and its products in sea food industry and inhalation of aeroallergens produced during shrimp processing. Exposure of shrimp in sensitized individual can induce anaphylaxis, skin symptoms, urticaria, and angioedema, gastrointestinal symptoms, respiratory symptoms (rhinitis and occupational asthma). The major shrimp allergens reported are tropomyosin and arginine kinase. Shrimp tropomyosin is a pan-allergen, which is cross-reactive with the tropomyosin of other crustaceans, mollusks, house dust mite, cockroach, and parasites. In sensitized individual, it is advised to avoid shrimp meat intake and exposure to shrimp meat (handling) to prevent allergic reactions.

Epidemiology

Worldwide distribution

Shellfish allergy is one of the most common food allergies, which may continue for a long time, usually persisting till adulthood. Among different crustacean species, shrimp is majorly responsible for allergy in adults and children. The prevalence of shellfish allergy ranges from 1.3 - 5.2%, based on the different dietary habits of various countries. Asians are reported to have a higher prevalence of shellfish allergy compared to the people in Western countries due to higher consumption of shellfish in this region. In the Philippines and Singapore shellfish allergy in teenagers was reported to be 5.12% and 5.23% respectively. A study conducted on children residing in Singapore showed more prevalence of shellfish allergy in native children as compared to non-native children. In the age group of 4-6years, the prevalence rate was 1.19% for native children and 0.55% for non-native children. Similarly, in the age group of 14-16 years, the prevalence rate was 5.23% for native children and 0.96% was for non-native children.

In another study conducted in Singapore by Thong et al. (2018) on 120 participants (of mean age 19.1± 1.5 years) with 64.2% having a food allergy, shellfish (78%) was the most commonly reported food and among different shellfish, shrimp was mostly responsible for causing oral allergy syndrome (OAS) in 30.3 % cases.

A study by Hao et al. (2018) reported a 12.4% prevalence of shrimp in 459 children and adults, based on a survey conducted in Hebei Province of China. Li et al. (2019) conducted a multicenter epidemiological survey in 35,549 schoolchildren (between 6 to 11 years) from rural and urban areas of India, China and Russia. Results stated that, in Hong Kong, shrimp was the most common food associated with sensitization besides egg and milk. In India and rural Shaoguan (China) sensitization against shrimp was quite high, about 10.3% and 13.1% respectively.

A population-based cross-sectional survey by Gupta et al. (2019) included 40,443 adults from the US. The results reported a 1.9% prevalence of shrimp allergy. A telephonic survey of 14,948 individuals in the US reported that 2-3% of individuals claimed to have a seafood allergy, out of which 2.2 % was due to shellfish. Children (0.5%) estimated to have a lower allergy rate as compared to adults (2.5%). Shrimp was found to be the most common cause of allergy followed by crab, lobster, clam, oyster, and mussel in the same decreasing order. In line with this survey, another study in the USA detected adults have a higher incidence of shellfish allergy (2.8%) as compared to children (0.6%) and women had more incidence (3.6%) as compared to men (2%).

A multi-center survey conducted in Europe showed IgE sensitization to shrimp was 4.8% among adults.

Shrimp allergy is highly prevalent in the Canarian Islands, due to the higher regional prevalence of house dust mite (HDM) allergy. A study evaluated parents (of Mexican school children aged 5-13 years) reported the prevalence of food allergy involving 1049 participants. Among all surveyed food in school children from Mexico, shrimp (1.3%) was found to be the major food for inducing hypersensitivity.

Risk factors

Individuals who are in the vicinity of cooking shellfish by boiling, steaming or frying are prone to develop allergic reactions by inhalation of vapors. Fishermen, processing workers, shell grinders, cooks, and even restaurant workers are at risk of developing allergic reactions to shellfish.

Pediatric issues

Adults are known to be more commonly affected compared with shellfish allergy compared to children. Moreover, in children, the anaphylaxis rate caused by shrimp was found to be lower compared to adults in a study. The precise reason for this mechanism was not clear. However, the probable reasons may be anaphylaxis rate has been artificially raised in the adult population as adults with less-severe allergic reactions would avoid causative food and won’t take medical attention. Secondly underreporting of anaphylaxis in children may occur because of risky behavior. Finally, some drugs taken by adults may lead to food-induced anaphylaxis.

Route Of Exposure

Main

The main route for shrimp exposure is through oral ingestion.

Secondary

Inhalation is another route of exposure. Workers working in the sea-food industry are exposed to air-borne shellfish particulate matter formed because of different processing activities such as filleting, freezing, cooking, smoking, drying which get suspended in the air as aerosols and can be inhaled.

Clinical Relevance

Oral allergy symptoms and Anaphylaxis

On exposure to shellfish, IgE-mediated allergic reactions may take place. The reactions can involve single or multiple organs and also allergic reactions may vary from immediate or late-phase (up to 8 hrs. after shellfish intake) reactions. Most frequently reported symptoms are oral allergic symptoms such as itching in the mouth and throat and lip swelling. In allergic patients, these reactions can induce further skin reactions such as urticaria, periorbital angioedema and skin redness and also gastrointestinal symptoms.

A study conducted by Chokshi et al. (2015) in the USA evaluated the rate of anaphylaxis with shrimp allergy, clinical presentation, and cross-reactive sensitization among children (< 18 years) allergic to shrimp. Results showed 68 patients were allergic to shrimp with a 12% rate of anaphylaxis. The most common clinical manifestation was mucocutaneous symptoms including skin symptoms (70%), urticaria (58%) and angioedema (58%). The patients more likely affected were males of African American or Asian ancestry with house dust mite or cockroach allergy. Also, a higher rate of eczema was observed in non-anaphylactic patients compared to the anaphylactic patient.

A case of a 16-year-old female was reported. She had a history of anaphylaxis to shellfish and allergic rhinitis (AR) to dust mite and cat. Her first allergic symptoms after eating shrimp (<20 mins) were swelling of the tongue and lips with pruritus, which resolved within 24 hours. However, the second reaction after eating shrimp rice (after 30 mins), was more severe, with allergic symptoms such as swelling of the periorbital area, lip, and tongue with hives. Further, tongue swelling increased which led to shortness of breath and required immediate medical attention. Her specific IgE (sIgE) level for shrimp was found to be high.

Shellfish is known to induce food-dependent exercise-induced anaphylaxis. It is important to consider if exercise was performed before an allergic response. Shellfish allergy has also proved to be the leading cause of food anaphylaxis in Hong Kong and Taiwan. One study in Singapore detected OAS and anaphylaxis symptoms due to different types of shellfish ingestion in 120 patients and compared the rate of OAS and anaphylaxis. The skin prick test was found to be positive for shrimp with symptoms of OAS in 87.1% and anaphylaxis in 100% positive cases.

Exposure of skin to the shellfish allergens takes place in occupational settings while handling and leads to urticaria or allergic contact dermatitis. There is a 3 to 11% prevalence of occupational contact dermatitis due to shellfish.

Allergic rhinitis

Lobster, shrimp, and crab are also known to cause occupational dermatitis, rhinitis, and conjunctivitis in fishermen and processing workers, cooks, restaurant workers.

Asthma

Shellfish are known to induce occupational asthma among workers, working in seafood processing plants and an estimated prevalence is about 2-36%. A case study by Goetz and colleagues (2000) found cross-reactivity of shrimp and scallops in a restaurant worker handling seafood. He developed IgE-mediated occupational asthma and contact urticaria. The allergen identified was a heat-stable protein with molecular masses ranging between 35 to 39 kD which may be tropomyosin. Also, boiling shellfish in an open containers may be a potential source of allergen which can induce respiratory allergic symptoms in cooks.

Prevention And Therapy

Prevention strategies

Avoidance

Avoidance of food responsible for causing allergy is the basic measure to control food allergies. Patients should be educated of possible exposure to hidden allergens in restaurants in terms of cooking equipment or serving utensils. Educating patient and family members about the diet intake, allergic symptoms its consequences and self-administration of anti-allergic medication (in an emergency). Also, shrimp (dried or paste) is present in instant noodles or soup, which can lead to accidental exposure. Patients that are allergic to shellfish like shrimp and lobster have to avoid the entire group of shellfish due to high cross-reactivity rates. Also, it is important to protect the consumer by accurate labeling of the food products to prevent a potentially life-threatening condition for allergic persons.

Cross-Reactivity

Pen a 1 (tropomyosin) is responsible for cross-reactivity among the members of the shellfish family, especially the crustaceans (such as prawns, crab and lobsters). Moreover, tropomyosin is an invertebrate pan allergen and reported to cross-react with the members of the class Arthropoda e.g. HDM (Der p1 10, Der f 10), with mollusks, and nematodes. According to a study finding, shrimp allergic patients are thought to show about 70% probability of positive skin prick test to crab and 78% probability with lobster.

In one occupational asthma patient, oysters and shrimps were found to be cross-reactive. Some recent case reports mentioned, ubiquitin, α -actin, and Pen m 2 (arginine kinase) may be associated with mite-seafood cross-reactivity. HDM allergens are the leading sensitizers for shrimp allergen in children and adults due to cross-reactivity as shown in a study.

Moreover, cockroach allergen Bla g 8 has 62.6 % similarity and 48.5% identity with shrimp myosin light chain allergen.