This Twitter summary from the 2013 meeting of the American College of Allergy, Asthma & Immunology (#ACAAI) was based on tweets by the following allergists/immunologists: Dr. Ellis @DrAnneEllis
Yesim Demirdag @DrYesimDem
Robert Silge, MD @DrSilge
Susan Bailey MD @subailey
Dr. Amal Assa'ad talk topic was: Can Food Allergy be Prevented?
There is a debate over when "atopy" starts. Prevention may have to occur during pregnancy or very early infancy.
Maternal diet and children risk
A Cochrane review of early inventions studies trying to prevent AD or food allergy showed that materially restricted diets did not work. The Cochrane review included evidence from 5 studies, and more than 950 patients -- maternal dietary avoidance does not prevent development of food allergy. In fact these restricted diets led to worse infant outcomes - low birth weight etc.
Maternal consumption of peanut and tree nuts may be inversely associated with development of asthma, ie eating nuts in pregnancy was good (Danish study).
In 1998 British recommendations were to avoid introduction of peanut into the diet until 3 year of age if family history of allergy. Hourihane studied the effect of this recommendation - there was no benefit with respect to prevention of peanut allergy, and the recommendation was rescinded.
Experts agree that avoiding highly allergenic foods in babies doesn't prevent food allergy. Feed peanut, milk, egg starting at 6 months. Peanut allergic patients who are skin/blood test negative to tree nuts rarely become tree nut allergic if they keep eating them.
Fetal cells are capable of producing IgE during the 2nd trimester. Others have shown that the IgE in cord blood belongs to the mother and not the baby.
C-section delivery was shown in a meta-analysis to increase the risk of allergy and atopic dermatitis.
In HealthNuts study from Melbourne, Australia, 21% of the population (1 yr-old) had a positive skin test to a food when defined by wheal bigger than 1 mm.
Allergic (atopic) march (click here to enlarge the image):
Food alternatives for patients with food allergy
Most patients with cow's milk allergy may tolerate horse, donkey, & camel milk, extensively hydrolyzed cow milk formula and elemental formula. The vast majority of patients with cow's milk allergy will cross react to goat's milk.
Dr. Bahna reminded the audience that risk of aerosolized peanut causing anaphylaxis is extremely, extremely low. He also emphasized the importance of controlling asthma in food allergic patients to reduce their risk of anaphylaxis on small exposure.
Another thought via Dr. Bahna: Peanuts are not tree nuts. Doughnuts are not nuts either.
Egg white is much more allergenic than egg yolk; cooking the egg extensively can often allow tolerance as well.
Fish oil may be tolerated by vast majority if patients with fish allergy.
8 foods cause 90% of food allergies (click to enlarge the image). The likelihood of a negative oral food challenge is shown in relation to the respective values of skin prick test (SPT) and serum IgE (sIgE):
Dietary factors play a role in food allergy
Fish and shellfish toxins such as vibrio, neurotoxin/saxitoxin, scombrotoxin, ciguatoxin may cause reactions resembling food allergy.
Fish parasites (Anisakis simplex) can cause allergic reactions, and they can be markedly reduced by deep freezing. Fish heavily infested with Anisakis larvae will produce symptoms of allergic reactions (parasite, natural defense is the eosinophil).
Comparison of raw vs boiled crustacean extracts - boiling actually changed the protein pattern and enhance the allergenicity. There is a very strong cross reactivity between shrimp and lobster. The allergenicity may be enhanced by cooking the crustaceans.
Roasted peanut is more allergenic than boiled peanut.
Refined peanut oil is free of peanut protein and is safe to consume. Non-refined peanut oil is expensive to produce and rarely used. Please note: the FDA allows peanut oil manufacturers not to list peanut as ingredient.
For milk and egg, 75% of patients may tolerate extensively heated allergens.
Cross-reactivity between food allergens
There is a strong cross reactivity between walnut, pecan, and hazelnut. There is no cross-reactivity between peanut and tree nuts, but one may be allergic to all. There is a moderate cross reactivity between cashew pistachio, Brazil nut and almond. No cross reactivity between peanut and tree nuts. However, 1/3 of tree nut allergic patients are also allergic to peanut. In one study peanut sensitization in tree nuts allergic patients was high (up to 60%) but true peanut allergy (proven by challenge) was found only in 30%.
Fruit seed allergy without fruit allergy is possible ( i.e. allergic reaction to juice but not the fruit).
Peanut component testing
Peanut component testing is more specific, but total peanut IgE is more sensitive. Level of Ara h 2 IgE do not correlate with severity of reactions (just like skin tests or IgE to peanut do not predict severity). Component testing is more likely to be informative with mild and remote reactions, low peanut IgE 0.35-15, in birch sensitized and older patients.
Food immunotherapy
Dr. Wesley Burks discussed food immunotherapy.
Food allergy has increased by 18% since 1997 in US, and 3 million school age children have food allergy.
Goals of immunotherapy are 2 fold:
- desensitization - you can tolerate more food than you could before but you are still allergic
- 2nd possible outcome is tolerance - long lasting remission from food allergy
The bulk of evidence suggests that OIT and SLIT are causing desensitization rather than tolerance.
Paradigm of food immunotherapy is very low dose to start, up-dosing phase, maintenance phase, desensitization and food challenge. Some studies include a tolerance evaluation phase, i.e. stop the OIT for a period of time and rechallenge.
For milk and egg 75%, of patients may tolerate extensively heated allergens.
Both oral IT (OIT) and sublingual IT have been studied for food allergy treatment. Desensitization magnitude of benefit is clearly greater with OIT than SLIT for food allergy.
In a CoFAR study, 50% of OIT treated egg allergic patients could pass an egg challenge. After stopping the OIT for 4 wks later, 27% still passed the challenge. This is no tolerance development.
During peanut oral immunotherapy Treg cells increase, IL5 and IL13 decrease, similarly to what we see in other immunotherapies.
In Burk's study on SLIT for peanut, 30 mg of peanut caused reactions at onset, patients needed about 900 mg to react at the end of the study (threshold was increased).
Side effects of OIT can be significant - and vary from GI symptoms to anaphylaxis - viral infection or fever are important risk factors for adverse events.
Anti-IgE (omalizumab, Xoliar) has been shown to increase the threshold doses, now being studied for ability to protect patients from side effects of OIT.
Chinese herbal therapy phase II (FAHF=2+ clinical trial is in progress for peanut, milk, egg, fish, shellfish, and sesame allergies.
The bulk of evidence suggests that OIT and SLIT are causing desensitization rather than tolerance.
Barriers to enrollment in OIT food trials include fear of baseline challenge, placebo arm and time constraints of study. Another major obstacle is funding - Dr. Burks stated that 1 coordinator needed per 25 patients.
Patch, epicutaneous immunotherapy for foods
VIASKIN® delivery system is for epicutaneous immunotherapy for foods - a patch is placed on the skin on ongoing basis (http://www.dbv-technologies.com/en/technology/viaskin-technology). A pilot milk study showed some evidence of desensitization with the patch, the magnitude was about the same as SLIT.
Question from the audience: Any role for nanoparticle delivery of food antigen? Dr. Burks replied that several studies are ongoing in animal models with nanoparticle delivery - no Phase I in humans yet.
What to expect when visiting an allergy clinic
Current allergy skin tests are virtually painless. This video by Dr. Bassett, a board-certified allergist from New York City, shows what to expect when visiting an allergy clinic for diagnosis and treatment: