Patients with fish allergies may also react to crocodile meat
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Individuals with fish allergies may be at risk for an allergic reaction to crocodile meat and should consult a specialist before consuming it, according to a study published in Pediatric Allergy and Immunology.
As part of their search for alternatives to fish for allergic individuals, the researchers traced this risk to the major fish allergen parvalbumin (PV) present in crocodile meat after observing a pair of anaphylaxis cases involving children with chicken and fish allergies related to PV who ate crocodile meat.
“It turned out that, to promote a healthy and safe diet, we had to also evaluate vertebrates other than bony fish for their potential to trigger an allergic reaction,” Andreas L. Lopata, PhD, associate professor and lead of the molecular allergy research laboratory at the Australian Institute of Tropical Health and Medicine, James Cook University, Townsville, Queensland, Australia, told Healio.
The study is part of a larger project on fish allergies involving more than 100 children from The Children’s Hospital at Westmead in Sydney, funded by the Australian Research Council and National Health and Medical Research Council, aiming for improved diagnostics and management, Lopata said.
“Crocodile meat is eaten worldwide by both children and adults. However, the published reports of anaphylaxis were in children who tried crocodile as an alternative to fish/chicken, which they had to avoid. Interestingly, Australia accounts for 60% of the global trade of crocodile products, including meat,” Lopata said.
Alpha PV, which can be found in cartilaginous fish such as shark and ray, is less allergenic than beta PV, which can be found in bony fish such as seabass and salmon. According to the researchers, up to 95% of individuals with fish allergies demonstrate IgE binding to beta PV in bony fish muscle. Crocodiles, the researchers noted, evolved from early bony fish.
Aiming to characterize the IgE binding proteins in crocodile meat, the researchers collected muscle tissue from saltwater crocodile, Asian seabass, Atlantic salmon, ghost shark and bluespotted stingray.
The researchers then recruited 77 children who had a history of IgE-mediated symptoms after eating fish. Skin prick testing to tuna, salmon and seabass produced positive results in 97% of these patients.
Next, eight of 12 of the subjects who were allergic to fish and who had SPT testing to crocodile demonstrated in vivo skin reactivity. By comparison, four individuals with shellfish allergy who received crocodile SPT showed no skin reactivity.
The researchers conducted analyses using commercial and in-house antibodies in addition to individual and pooled patients’ serum to identify and quantify IgE binding proteins, finding that 44 patients (57%) had IgE binding to at least one PV isoform.
Specifically, 31 (70%) showed IgE binding to crocodile PV, 13 (30%) showed IgE binding to both alpha and beta PV, 14 (32%) showed IgE binding only to beta PV and four (9%) showed IgE binding only to alpha PV. Plus, according to the researchers, the signal to beta PV was up to 500 times stronger than the signal to alpha PV.
Although alpha PV was the most abundant isoform, the researchers found that beta PV was more frequently and more strongly recognized by IgE antibodies likely because of its greater similarity including sequence identity to beta PVs in fish, making it the major IgE-binding allergen in bony fish and crocodile.
“The major crocodile protein allergen, parvalbumin, has a higher IgE-antibody binding capacity than some fish parvalbumin. Generally, most cartilaginous fish (sharks and rays) and some bony fish appear much safer than crocodile for fish-allergic patients,” Lopata said.
The researchers assigned Cro p 1 to crocodile beta PV and Cro p 2 to crocodile alpha PV as allergen names and registered them with WHO and the International Union of Immunological Societies.
“Crocodiles are much more dangerous than we ever thought, even when dead on the plate,” Lopata said.
Lopata cautioned patients with fish allergies to avoid consuming alligator and crocodile meat unless medical providers have confirmed their tolerance.
“Fish allergy is highly complex with over a thousand different species consumed worldwide. Because of limited diagnostic capacity, it can be best to recommend the avoidance of all fish and fish products. However, the allergy is often species-specific and can extend to meat from other vertebrates such as crocodiles,” Lopata said.
Also, Lopata said, doctors should be aware of the fish-crocodile syndrome, be cautious about recommending alternatives to fish for allergic individuals and advocate for the development of better diagnostic and management tools.
The researchers also called for further research to improve the accuracy of determining the clinical relevance of novel allergens, including the development of corresponding blood diagnostics and management tools, which could prevent the need for oral food challenges. Currently, the researchers are exploring alternative menus for people with food allergies as well.
For more information:
Andreas L. Lopata, PhD, can be reached at andreas.lopata@jcu.edu.au.
Perspective
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Jennifer Bufford, MS, CRQM, CCRP, CCRC
Cross-reactivity in allergic reactions occurs when the proteins in one substance are similar to the proteins found in another substance. As a result, the immune system sees them as the same. In the case of food allergies, cross-reactivity can occur between one food and another. More than 70% identity in the primary sequence is generally needed for cross-reactivity.
Examples of food families with high rates of cross-reactivity include mammalian milks, eggs, fish, shellfish and certain tree nuts. Low rates are noted for grains such as wheat, barley and rye, and rates of cross-reactivity are variable for most other foods.
Cross-reactivity can also happen between pollen and foods or latex and foods. For example, if you are allergic to birch tree pollen, you may also find that eating apples causes a reaction for you.
Also, positive SPT responses to multiple fish in patients with fish allergy is almost the rule, and clinical cross-reactivity is common.
If a person has a measurable reaction to a certain food with clinical diagnosis, avoiding similar foods that could trigger this reaction may be helpful. Fish-allergic individuals, then, should consult with their allergist before consuming crocodilian meat.
This research resulted in the identification of the major allergenic protein, which could help investigators develop a purified extract to aid diagnosis. Such a purified extract could potentially be employed for oral, sublingual or epicutaneous immunotherapy.
Cross-reactivity between fish and crocodile could further be investigated by conducting a study that uses oral food challenges, which are the gold standard for diagnosing a food allergy. Relying solely on a positive IgE response or SPT is insufficient to definitively conclude the presence of a food allergy. The only reliable measure is a failed OFC. In the absence of such data, the authors may be overestimating the prevalence of allergy to crocodile meat.
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