Catfish
Summary
Catfish belong to the order Siluriformes, which encompasses several families, including genera like Ictalurus and Pangasius. Catfish are significant in aquaculture and fisheries, providing food and economic value. Ingestion is the primary route of exposure to catfish allergens, leading to symptoms ranging from mild oral allergy reactions and localized urticaria to severe anaphylactic responses. The major fish allergen parvalbumin has been detected in catfish. IgE cross-reactivity between allergens from catfish and other fish species—such as tilapia, tuna, herring, salmon, halibut, grass carp, cod, and grouper, has been documented. Cross-reactivity between catfish allergens within the order Siluriformes can be expected. Diagnosis of fish allergy involves evaluating the patient’s medical history along with diagnostic tests such as specific IgE measurements and skin prick tests. Oral food challenge is sometimes performed when deemed necessary. Management of fish allergies typically involves avoiding foods that contain fish products.
Epidemiology
Worldwide distribution
Fish is a frequent cause of food allergies, especially in coastal areas where the supply of fish is high. Prevalence varies across regions, with some Asian countries, such as the Philippines (2.3%) and Korea (12.5%), reporting higher prevalence than the U.S. (< 0.5%).
A multicenter, retrospective observational study conducted between 2015 and 2019 analyzed 945 patients (age range: 0–90 years) with seafood allergies from seven hospitals in the US and the UK. Of these, 694 were from the U.S. and 251 from the U.K. Fish allergy prevalence among U.S. patients was 45.8% (318/694), while only 7.6% (19/251) of U.K. patients were affected. Among the 645 U.S. patients with available sensitization data, 5.4% tested positive for specific(s) IgE to fish allergens, with 2.9% testing positive specifically for catfish. On the other hand, of the 185 U.K. patients with available sensitization data, 52.4% had a positive specific IgE to at least one fish allergen. The most common fish causing allergies were cod, salmon, mackerel, and tuna.
Another U.S.-based retrospective study involving 5,162 patients (aged ≥ 18 years) conducted during 1997–2010 found that 640 patients had physician-recorded food allergies. Of these, 24.8% (159/640) had a seafood allergy. Among those with seafood allergies, 22 patients (13.8%) were allergic to fish. Tuna was the most common trigger of allergy (28.6%), followed by catfish (23.8%) and salmon (23.8%).
Risk factors
The presence of concomitant asthma and eczema are common risk factors for fish allergy. A study involving 249 children (median age: 4.2 years) with a history of fish allergy and confirmed sensitization through skin prick test (SPT) or specific IgE testing, reported a significant correlation between catfish-specific IgE levels and the severity of atopic dermatitis (AD).
Pediatric issues
Fish allergy often continues into adulthood and is recognized as a trigger of anaphylaxis in young children. A cross-sectional study conducted in Thailand on 11 children (median age: 3 years) with IgE-mediated fish allergies reported catfish (4/11) and tilapia (4/11) as the most common triggers, followed by salmon (3/11). The levels of specific IgE to catfish in ten of the children in the study ranged from 0.23 to 22.6 kUA/L. The IgE levels for catfish, salmon, cod, tilapia, and tuna in the remaining child were measured at 0 to 0.06 kUA/L.
Another study involving 249 children (median age: 4.2 years) with a history of fish allergy and confirmed sensitization found that the median specific IgE levels for tilapia (4.88 kUA/L) and catfish (4.35 kUA/L) were higher than those for most other fish species, which generally had specific IgE levels below 4 kUA/L. Notably, catfish was identified as one of the least tolerated fish among these children.
Route Of Exposure
Main
Ingestion is the primary route of exposure to catfish allergens, leading to allergic reactions in sensitized individuals.
Clinical Relevance
Bony fish, such as catfish, cod, and salmon, are more commonly associated with allergies due to their higher allergen content compared to cartilaginous fish like shark, ray, and ghost sharks. Exposure to these allergens can trigger allergic reactions affecting multiple organ systems, with symptoms varying from mild oral allergy symptoms and localized urticaria to severe anaphylactic reactions.
Angioedema, urticaria, and anaphylaxis
In a study involving 10 patients (5 children and 5 adults), a 2-year-old female child with a confirmed catfish allergy—demonstrated by a double-blind placebo-controlled food challenge (DBPCFC)—experienced symptoms of angioedema and generalized urticaria upon ingestion of catfish. Among the 5 adults, a 25-year-old female with a positive DBPCFC to catfish, cod, and snapper had previously experienced anaphylaxis upon ingesting these fish species.
In another study conducted on 5,162 patients with food allergies, 5 patients experienced allergic reactions after consuming catfish, all of whom reported skin symptoms such as angioedema, urticaria, flushing, and pruritus.
Respiratory
A study conducted on 5,162 patients with food allergies found that, among the 5 patients experiencing allergic reactions after consuming catfish, only 1 developed respiratory symptoms such as cough, dyspnea, wheezing, chest tightness, and throat swelling.
Eye/Nasal
Eye and nasal symptoms—such as ocular pruritus, coryza, rhinorrhea, nasal congestion, nasal itching, and sneezing—were reported in 1 out of 5 patients who experienced allergic reactions to catfish in a study conducted on 5,162 patients with food allergies.
Atopic dermatitis
A study conducted on 10 patients (5 children and 5 adults) reported that a 2-year-old female child experienced AD after ingesting catfish. Her catfish allergy was confirmed by a DBPCFC.
Diagnostics
Diagnosis of fish allergies generally involves an assessment of medical history along with diagnostic tests such as specific IgE measurement and skin prick testing (SPT). In some cases, oral food challenge (ideally, double-blind placebo-controlled challenge) with the fish that has elicited the reaction is considered. Component-resolved diagnostics (CRD) is an emerging diagnostic technique that can help identify the specific culprit allergen and cross-reactivity patterns. At present, only a limited fish allergens (cod and carp parvalbumin) are currently available for CRD testing.
In a study following the natural history of fish allergy it was found that it will resolve spontaneously by adolescence in a considerable proportion of children, particularly in cases with less severe reactions and a lower level of sensitization. Thus, diagnostic reassessment of fish allergic children, at regular intervals, depending on age, and patient's history, may be considered to identify possible development of spontaneous tolerance.
Prevention And Therapy
Prevention strategies
The management of fish allergies typically involves completely avoiding fish and foods that contain fish products due to the risk of severe allergic reactions. Therefore, accurate food labeling is essential to ensure the safety of affected individuals.
Cross-Reactivity
Cross-reactivity is commonly observed among parvalbumins of different fish species, especially those belonging to the same family or genus, as they share common IgE epitopes. A study involving 249 children found that 88% of patients were cross-sensitized to parvalbumins from several fish species, including catfish, tilapia, tuna, herring, salmon, halibut, grass carp, cod, and grouper. An immunoblot inhibition study using cod fish extract and serum from a pediatric and an adult patient with fish allergy showed complete inhibition of IgE binding to a catfish protein of size 12.5 kDa—similar in size to cod parvalbumin.
Explained Results
Allergen information
Channel catfish (I. punctatus) is a commercially important species in the family Ictaluridae. Consumption of catfish can cause allergic reactions in sensitized individuals. The major fish allergen parvalbumin has been detected in channel catfish.
Clinical information
Clinical manifestations following exposure to fish allergens can range from mild symptoms such as local urticaria and oral allergy symptoms, to severe anaphylactic reactions.
Cross-reactivity
IgE-mediated cross-reactivity has been observed among several fish species, including catfish, tilapia, tuna, herring, salmon, halibut, grass carp, cod, and grouper.
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