Peanuts, Allergy, and Travel
Abstract & Commentary
Synopsis: Repeated injections of a monoclonal anti-IgE antibody markedly decreased the sensitivity of peanut-allergic patients to subsequent peanut exposure. Since fatal anaphylaxis to peanuts can occur following inadvertent ingestion of small amounts of peanut antigen, this treatment might be very useful for peanut-allergic travelers who will be exposed to foods of uncertain purity.
Source: Leung DYM, et al. N Engl J Med. 2003;348:986-993.
TNX-901 is an IgG1 monoclonal anti-ige antibody that hinders binding of IgE to mast cell and basophil receptors. A multicenter, randomized, double-blind, dose-ranging interventional trial was done in 84 peanut-allergic patients. Following a series of subcutaneously injected TNX-901 doses, subjects were orally challenged with peanuts. The threshold at which subjects responded with a sensitivity reaction was noted. There was a significant positive correlation between the dose of TNX-901 and the increase in reaction threshold. At the highest dose tested, the mean dose of peanuts to which subjects reacted increased from 178 mg (about half a peanut) to 2805 mg (about 9 peanuts).
Comment by Phillip R. Fischer, MD, DTM&H
Approximately 15% of individuals have allergic disease, and food allergies are a significant problem for some of these people. Peanuts are among the foods most likely to trigger serious reactions, and fatal anaphylaxis is a possible outcome. In a series of 7 cases of fatal anaphylaxis, each individual was atopic with a prior history of anaphylaxis; triggering foods included peanuts (4 cases), pecan, crab, and fish.1 In a separate report of serious anaphylactic reactions in children (6 fatal and 7 near-fatal), each affected child was previously known to have food allergies, and most were asthmatic; triggering foods included nuts (6 cases) and peanuts (4 cases) as well as milk and eggs (fewer cases).2 Some children are allergic to multiple different foods, and significant exposures are commonly inadvertently related to hidden or unknown food ingredients.3 While milk and egg allergies commonly resolve during childhood, peanut allergies often persist throughout life.
It is particularly concerning that reactions to peanuts can occur after exposure to very small amounts of allergen.4 While most significant exposures result from inadvertently eating food that contained peanut material, some authors have expressed concern that air filters in commercial aircraft have been found to contain peanut allergen and are only changed every 5000 hours.5 Many peanut-sensitive travelers fear exposure to peanuts during air travel as well as when eating foods of unknown composition during their trips. Some airlines have offered peanut-free flights to help allay these fears.
In the context of travel, the recent New England Journal of Medicine paper offers great hope to peanut-allergic individuals. Leung and associates found that peanut-sensitive patients were much less likely to respond to peanut exposure 2-4 weeks after completing a course of 4 subcutaneous injections at 4-week intervals of TNX-901. In fact, subjects increased their threshold of response to a level that could likely not occur due to inadvertent ingestion on an airplane or by eating food contaminated with peanuts during processing. If further studies confirm these findings, this "peanut allergy vaccine" could markedly decrease both anxiety and the risk of fatal anaphylaxis in peanut-sensitive travelers.
Similarly favorable results with a different anti-IgE product have been reported for asthma treatment. As reported in the New York Times (March 11, 2003), however, commercial and marketing decisions might delay further study and the potential availability of any of these products for peanut-allergic individuals.
So, what can peanut-sensitive travelers do right now while they await the availability of anti-IgE products? First, they should continue to pay attention to food preparation and labeling in an effort to avoid inadvertent ingestion of peanut-containing products. Second, they can be reassured to know that fatal reactions rarely occur in people without previous knowledge of their food allergy. Furthermore, fatal outcomes are rare when epinephrine is given within 30 minutes of the inciting ingestion. Epinephrine is the treatment of choice for anaphylaxis, and at-risk travelers should have epinephrine available during trips while realizing that they should check expiration dates to ensure that the epinephrine is still effective at the time they travel. Travel medicine practitioners can seek a history of serious allergic reactions and provide epinephrine when indicated, along with documentation of the need for this injectable product to help travelers avoid delays when crossing international borders. Travelers can also be advised that epinephrine reaches a peak plasma concentration more quickly (8 vs 34 minutes) following intramuscular rather than subcutaneous injection.6
While presumptive treatment of allergic reactions is useful, it would be better to prevent the development of allergies. What causes food allergies in the first place? Parallel to the TNX-901 article, the New England Journal of Medicine published a paper reviewing epidemiologic associations with the development of peanut allergy in children.7 There was no link between pediatric peanut allergy and preceding prenatal exposure to maternal dietary factors. There was, however, a link between the use of peanut oil on inflamed skin during the first 6 months of life and subsequent peanut allergy.
Similarly, peanut allergy was more common in children who had used soy milk or soy formula. Pending interventional studies, it might be wise for infants to avoid the topical use of humidifying lotions that contain peanut oil, and it could be sensible to limit the use of soy formulas to those children with clear-cut need for them.
Does vaccination prompt people to develop allergies? A recent, detailed review concluded that "large well-controlled epidemiologic studies do not support the hypothesis that vaccines cause allergies."8 Furthermore, another recent report showed that routine childhood vaccination actually protects against the development of atopy in the first years of life.9 Travel medicine providers need not shy away from appropriate vaccination due to concerns about stimulating allergic disease.
In summary, there is exciting progress in the management of individuals with peanut allergy. At the same time, travel medicine practitioners should continue their efforts to provide appropriate pretravel guidance that includes the provision of appropriate medication and counsel for allergic travelers, and they should continue giving pretravel vaccines without fear that vaccines cause allergies.
1. Yunginger JW, et al. JAMA. 1988;260:1450-1452.
2. Sampson HA, et al. N Engl J Med. 1992;327:380-384.
3. Sicherer SH, et al. Pediatrics. 1998;102(1):e6.
4. Hourihane JO, et al. Clin Exp Allergy. 1997;27:634-639.
5. Jones RT, et al. J Allergy Clin Immunol. 1996; 97:abstract 961.
6. Simons FE, et al. J Allergy Clin Immunol. 1998;101: 33-37.
7. Lack G, et al. N Engl J Med. 2003;348:977-985.
8. Offit PA, et al. Pediatrics. 2003;111:653-659.
9. Gruber C, et al. Pediatrics. 2003;111:666.
Dr. Fischer is Professor of Pediatrics, Department of Pediatric & Adolescent Medicine, Mayo Clinic, Rochester, MN.