f000 Common Carp

Summary

The common carp (Cyprinus carpio) is among the most widely cultivated freshwater fish globally, valued for its economic significance and adaptability. It has two primary forms: C. carpio morpha hungaricus, characterized by an elongated body, and C. carpio morpha acuminatus, which has a shorter, compact build and a pronounced shoulder. Fish allergies are reported in 0.2% to 2.29% of the general population, with prevalence reaching up to 8% among fish processing workers due to occupational exposure. The allergenic potential of common carp primarily arises from beta-parvalbumin, a calcium-binding protein abundant in the muscles of bony fish. Clinical symptoms of carp allergies include urticaria, angioedema, gastrointestinal issues, respiratory distress, and, in severe cases, anaphylaxis. Exposure to carp allergens occurs primarily through ingestion but may also result from inhaling aerosolized proteins during cooking or processing, and as direct skin contact while handling fish. Testing for sensitization typically involves skin prick tests and specific IgE testing. Avoidance remains the primary strategy for managing fish allergies.

Allergen      

Nature

The common carp (Cyprinus carpio) is among the most widely cultivated and commercially significant freshwater fish species globally (Barakov et al. 2024, FAO 2024). This species has two main forms: C. carpio morpha hungaricus and C. carpio morpha acuminatus. The former is known for its elongated, torpedo-like body, while the latter has a shorter, more compact build with a pronounced shoulder. Body coloration varies from gray and silver to bronze, often with a yellow or reddish underside (FAO 2024).

Common carp is distinguished by its elongated dorsal fin, which contains 2–3 hard rays and 17–22 soft rays. This species has been introduced to almost every country with environmental conditions favorable for reproduction. In many of these environments, it is considered an invasive species, prompting efforts to reduce or eradicate its population (FAO 2024).

Habitat

The common carp belongs to the largest family of fish found in freshwater habitats, Cyprinidae. It thrives in lakes, ponds, reservoirs, rivers and has spread worldwide (Sližienė et al. 2022).

Taxonomy

The common carp is classified under the clade Osteichthyes (bony fishes), within the order Cypriniformes, and the family Cyprinidae (FAO 2024).

Taxonomic tree of C. carpio (NCBI 2020)

Tissue

Fish muscle is the primary source of allergenic activity, with parvalbumin identified as the main allergen (Mastrorilli et al. 2023). Parvalbumins (10–12.5 kDa) are structurally related to calmodulin and troponin C (Mukherjee et al. 2023). Most fish-allergic individuals are sensitized to beta-parvalbumin, a calcium-binding protein abundant in the muscles of bony fish. Although beta-parvalbumin has a simple structure, it exists in various isoforms (as monomers or aggregates), which may influence its allergenicity (Perez-Tavarez et al. 2021).

Research shows that parvalbumin levels are lower in posterior muscles compared to anterior and middle muscles (Lee et al. 2012). The level of parvalbumin also varies among different fish species (Dijkema et al. 2022). For example, one study found that parvalbumin levels in mackerel were below 0.5 mg/g, ranged from 0.5 to 2 mg in trout and salmon, and exceeded 2 mg in carp, cod, redfish, and herring (Kuehn et al. 2010). Notably, herring and carp have high parvalbumin concentrations of up to 5 mg per gram of muscle tissue, whereas tuna contains only trace amounts, around 0.03 mg per gram (Dickel et al. 2021).

In addition to parvalbumin, aldolase, beta-enolase, collagen, tropomyosin, and vitellogenin are recognized as less common fish allergens (Sližienė et al. 2022, Mastrorilli et al. 2023).

Epidemiology                   

Worldwide distribution

The prevalence of self-reported fish allergy ranges from 0.2% to 2.29% in the general population, rising to as much as 8% among fish processing workers (Sharp et al. 2014). The common carp is among the most widely eaten and extensively farmed fish species and is known to cause allergy symptoms in individuals sensitized to fish (Sližienė et al. 2022).

A multicenter cross-sectional observational clinical survey on fish allergy involving 56 patients was conducted across six allergy centers in Italy. Among these participants, 67.8% tested positive for the single beta-parvalbumin Cyp c 1. Overall, 92.8% of the patients tested positive for at least one beta-parvalbumin (Villalta et al. 2022).

Another study included 26 patients (both children and adults) with confirmed fish allergies from Greece, the Netherlands, and Spain. Patients were identified based on detailed case histories and confirmed positive specific IgE levels. In 73% of the patients’ sera, IgE-binding activities were found to be comparable between purified natural and recombinant beta-parvalbumins from cod and recombinant beta-parvalbumin from carp (Ma et al. 2008).

Risk factors

Genetic and environmental factors, both prenatal and postnatal, have been identified as significant risk factors for food allergies. Research highlights the role of heredity in the development of atopy and the production of IgE (Kaza et al. 2007). Moreover, fish sensitization can occur through damaged skin barriers in individuals with pre-existing atopy and hand eczema (Klueber et al. 2019). Delaying the introduction of complementary foods has also been associated with an elevated risk of developing allergies (Jonsson et al. 2017).

Pediatric issues

A cross-sectional telephonic survey conducted across the USA revealed that the prevalence of fish allergies is significantly lower in children in comparison to adults, with rates of 0.2% and 0.5%, respectively (Sicherer et al. 2004). In a study conducted in Hong Kong, 69 participants with physician-diagnosed IgE-mediated grass carp allergy, aged 2 to 16 years, were recruited from all four pediatric allergy referral centers in the region. The study focused on examining the molecular characteristics of grass carp parvalbumin Cten i 1 and its allergenicity. Among the allergens tested, IgE reactivity was highest for Cten i 1, followed by Cyp c 1 (common carp) and Gad m 1 (cod) (Leung et al. 2020).

A study conducted in Luxembourg included 18 patients with fish allergies (mean age 16 years) and 7 control subjects to assess clinical reactivity to a cartilaginous fish (ray fish) and IgE responses to parvalbumins from both bony and cartilaginous fish. Positive reactions to at least one parvalbumin were observed in 78% of the allergic individuals, all of whom demonstrated sensitivity to beta-parvalbumins. (Kalic et al. 2019).

Environmental characteristics            

Living environment

The common carp thrives in water temperatures ranging from 3°C to 35°C, with an optimal range of 20°C to 25°C for growth and reproduction. In their natural habitat, it is typically found in the middle and lower reaches of rivers, favoring shallow waters only a few meters deep with muddy substrates (FAO 2024).

Worldwide distribution

The common carp is widely distributed across the globe, including regions in Asia, Europe, Africa, North America, and Australia (Sližienė et al. 2022).

Route of exposure            

Main

The primary pathway of fish sensitization is through ingestion via the gastrointestinal tract, where allergens interact with the intestinal epithelium (Sharp et al. 2014, Mastrorilli et al. 2023).

Secondary

The secondary route of exposure involves inhalation of fish proteins, which is particularly relevant in both domestic and occupational environments. Patients with fish allergies may react to aerosolized proteins released during the cooking or processing of fish. Additionally, allergen exposure can occur through skin contact while handling and preparing fish (Sharp et al. 2014).

Clinical relevance           

The most common hypersensitive reaction to fish is IgE-mediated (Kalic et al. 2021). Patients sensitive to one or multiple fish species may experience symptoms such as vomiting, urticaria, diarrhea, and coughing. Clinical symptoms of allergy may differ based on the cooking method used, eating habits, and the type of fish consumed, potentially affecting the respiratory, skin, and digestive systems. Fish allergies can also cause severe reactions, including anaphylactic shock in certain cases (Sližienė et al. 2022).

Cutaneous and gastrointestinal symptoms

In a study, 68 patients tested positive for the common carp allergen (Cyp c 1) and presented clinical symptoms such as angioedema, contact urticaria, erythema, gastrointestinal issues, and oral reactions (Leung et al. 2020).

Anaphylaxis and respiratory symptoms

The common carp allergen has also been associated with anaphylaxis and respiratory symptoms (Leung et al. 2020).

Diagnostic relevance

The existing clinical approaches to diagnosing fish allergies are clinical assessment, specific IgE testing, skin prick test (SPT) and oral food challenge. An accurate diagnosis requires a detailed history of the allergic episode, including information on the timing, duration, type, and quantity of fish consumed, as well as symptoms affecting the skin, mucous membranes, cardiovascular, respiratory, and neurological systems. Accurate diagnosis should consider the fish species commonly consumed in specific geographic regions. For instance, while various species of carp are widely eaten in some parts of Asia, they are not considered among the most frequently eaten fish in the USA and Europe (Kalic et al. 2021).

Prevention and therapy

Avoidance

Avoidance of fish is strongly recommended for individuals with fish allergies.

Allergen specific immunotherapy is currently not available.

Molecular aspects            

Allergenic molecules

As of December 10, 2024, the World Health Organization/International Union of Immunological Societies (WHO/IUIS) allergen nomenclature database lists two allergens from the common carp (C. carpio). The details are outlined below.

Cross-reactivity

Cyp c1, the carp beta-parvalbumin, is the major fish allergen and exhibits broad cross-reactivity among most fish species (Agabriel et al. 2010).

The parvalbumin isoforms Cyp c 1.0101 and Cyp c 1.0201 from common carp showed the highest sequence homology with other bony fish species, such as silver hake, toadfish, whiting, chub, Atlantic salmon, and pike (Swoboda et al. 2002). Similarly, the 9 kDa parvalbumin (Cten i 1) from grass carp was found to exhibit a high amino acid sequence homology (91.7%) with Cyp c 1 (Leung et al. 2020).

Parvalbumins from sharks and various bony fish species (carp, cod, and salmon), share amino acid sequence homology of less than 50%.

A high sequence identity has been observed between bony fish parvalbumins and muscle parvalbumins from amphibians, birds, and reptiles (Stephen et al. 2017).

Explained results

Allergen Information

The common carp is one of the most widely consumed and extensively farmed fish species, recognized for its potential to trigger allergic reactions in sensitized individuals (Sližienė et al. 2022). Two allergens have been identified in carp: Cyp c 1 (beta-parvalbumin) and Cyp c 2 (beta-enolase), with beta-parvalbumin being the major allergen. (Agabriel et al. 2010, WHO/IUIS 2019, WHO/IUIS 2020). Carp muscle tissue contains a high concentration of parvalbumin, reaching up to 5 mg per gram (Dickel et al. 2021).

Clinical information

Fish allergies, primarily IgE-mediated, can cause symptoms such as urticaria, gastrointestinal issues, respiratory distress, and, in severe cases, anaphylaxis. Reactions may vary based on the type of fish and its preparation methods (Kalic et al. 2021, Sližienė et al. 2022). The common carp allergens, particularly Cyp c1, has been linked to angioedema, contact urticaria, erythema, gastrointestinal issues, oral reactions, and respiratory symptoms (Leung et al. 2020). Notably, a documented case reported anaphylaxis triggered by cutaneous exposure to cyprinids (De Aramburu Mera et al. 2020).

Cross-reactivity

Cyp c1, the carp beta-parvalbumin, is the primary allergen and demonstrates extensive IgE cross-reactivity with parvalbumins from various fish species, including salmon, cod, and mackerel. Studies have also revealed significant amino acid sequence homologies between carp parvalbumins and those from other fish, amphibians, reptiles, and birds (Swoboda et al. 2002, Kalic et al. 2019).

Author: Turacoz

Reviewer: Dr. Michael Spangfort