Summary

Herring (Clupea harengus L.) has been a valuable commercial fish since the medieval period and is usually consumed in various processed forms like salted, marinated, smoked, and canned due to its high amounts of vitamin D, long-chain polyunsaturated fatty acids, and calcium. It is prevalently found in the Northeast and Northwest Atlantic. Furthermore, the Baltic Sea, North Sea, and the coastal waters of Canada, Britain, Iceland, Norway are the prime fishing grounds for herring. The prevalence of fish allergy is found to be higher in countries with high fish consumption and fish-processing industries. Herring allergy is primarily induced through the oral route and secondarily through exposure to vapors (while processing the fish) and through skin contact. Therefore, consumption of herring by sensitized individuals may trigger oral symptoms, respiratory symptoms (asthma, frequent sneezing, dyspnea, irritable running nose), and allergic contact dermatitis. In herring, Clu h 1 (Beta-parvalbumin), a 12 kDa calcium-binding and heat-resistant protein, is the major allergen found in the fish muscle. Herring has been reported to possess cross-reactivity with Anchovy, Sardine, Pacific herring. Furthermore, herring parvalbumin is also cross-reactive with parvalbumins from salmon (Sal s 1), pollock (The c 1), wolfish, Baltic cod (Gad c 1), and Atlantic cod (Gad m 1).

Epidemiology

Worldwide distribution

Seafood allergy (fish and shellfish) is regarded as one of the most common causes of allergy in coastal areas. Moreover, this allergy has been reported to be prevalent in eastern countries like Singapore and Japan.

The prevalence of fish allergy is found to be higher in countries with high fish consumption and fish-processing industries. In Asia, the Philippines has been reported to have the highest prevalence (2.29%) of fish allergy compared to Singapore (0.26%) and Thailand (0.29%).

Furthermore, in European countries, the prevalence of fish allergy in the adult population was found to be about 0.8% and is a little higher than the children. The countrywide prevalence of clinically confirmed fish allergy in the pediatric population in Europe was found to be 0.7 % in Sweden (4 years old), 0.6% in Germany (2-6 years old), and 5% in Finland (1-4 years old). In Norway, fish hypersensitivity is frequently reported due to occupational exposure in the fish industry and its extensive consumption. Furthermore, fish allergy has been found to be affecting around 0.1% of the country's population.

A US-based cross-sectional survey reported seafood allergy in 2.3% of the general population, of which 2% was for shellfish, 0.4% for fish, and 0.2% for both fish and shellfish.

According to a Denmark-based study conducted among fish-factory workers, the prevalence of herring allergy was reported to be around 13%.

A population study conducted in Germany confirmed 0.5% as the prevalence of herring allergy among the adult population.

Risk factors

Parvalbumin, a major allergenic protein in fish, is found to be highly heat-resistant. Therefore, processing the fish might not be helpful in decreasing the parvalbumin-mediated allergenicity.

Furthermore, fish parvalbumin-sensitized patients with antacid medication are claimed to be at an increased risk of developing severe reactions compared to others.

Additionally, around 50% of individuals allergic to certain fish are also found to be at risk of reacting to other fish species.

Route Of Exposure

Main

Ingestion of fish is considered the route of exposure that may cause IgE-mediated hypersensitivity.

Moreover, inhalation of fish allergens is found to be one of the routes of exposure (occurs during outdoor drying, fish odors, and fumes produced during cooking). Furthermore, direct skin contact with the fish has also been reported as a route of exposure that can occur while cooking or processing the fish.

Clinical Relevance

Fish allergy has been observed commonly among children and young adults and may be associated with symptoms like oral allergy syndrome, asthma, and allergic contact dermatitis.

Oral symptoms

According to a study, 79% (15/19) of the fish-allergic patients were found to exhibit allergic symptoms after the consumption of herring.

Furthermore, another study confirmed the presence of IgE antibodies to herring among fish-allergic adults. Moreover, the study also reported clinical sensitivity (0.93) and specificity (0.87) towards herring.

Respiratory symptoms

According to a study, asthma was reported among 21% (4/19) fish-factory workers. Furthermore, the study also confirmed around 32% (6/19) of the fish-factory workers possess work-related respiratory symptoms.

Dyspnea (6.1%), frequent sneezing (9.1%), and irritable, running nose (18.2%) was reported by a study conducted among production workers (n=11) working in herring plant.

Atopic dermatitis

A study reported the presence of IgE antibodies to herring in patients with atopic dermatitis.

Moreover, a case study also found specific anti-herring IgE antibodies in the serum of a patient with occupational protein contact dermatitis.

Diagnostics

Parvalbumin can be extensively utilized to diagnose and manage fish allergy through parvalbumin-specific IgE testing.

Prevention And Therapy

Prevention strategies

Avoidance

Complete avoidance of fish and fish-based food products from the diet can be considered as preventive measures for fish allergy. In addition, to avoid accidental consumption, individuals allergic to fish are usually advised to cross-check the packaged food labels extensively before consuming any retail food products.

Cross-Reactivity

Herring is found to exhibit cross-reactivity with other fishes from the Clupeiformes order (like Anchovy and Sardine). A strong cross-reactivity has also been reported between Atlantic herring and Pacific herring.

Furthermore, herring have been found to be highly cross-reactive (parvalbumin-based) with other fish species like Salmon, Wolfish, Baltic cod, Pollock, and Atlantic cod.