A. Case study
B. More information
C. Editors' comments
D. References
E. CPD questions (South Africa



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A. Case study
A baby boy was exclusively breastfed from birth and presented with eczema at the age of 3 months. Serum-specific IgE tests were done, and showed a positive response to cow's milk, peanut and egg. The mother excluded these foods from her diet and continued to breastfeed her son. The eczema improved dramatically. At the age of 10 months, the eczema presented again. At this stage, the child was still being breastfed, and also received solid foods, but nothing containing cow's milk, peanut or egg.

Doing a thorough clinical history of the mother and child's diets could indicate whether all sources of cow's milk, peanut and egg had been excluded from the child's diet. A history was done and showed complete exclusion. Other factors that influence the flaring of eczema (i.e., exposure to house dust mite, smoking, pets, perfumes, fabric softeners, etc.) were also investigated, but there were no significant changes over the last 7 months.

Would it be worth redoing the serum-specific IgE tests? The advantage of redoing the tests is that one can determine how compliant the patient has been with the exclusion of the culprit foods from the diet. If the patient has been compliant, one would expect the serum-IgE to be decreased since the last test, but if the serum-IgE is stable or increased, this indicates possible non-compliance. Serum-specific IgE tests were done for cow's milk, peanut and egg. The results showed that the serum-IgE to peanut was raised and that the serum-IgE levels to the other foods were low. This would indicate that peanut sources might still be present in the diet.

The mother denied any exposure to peanut in her and the child's diet. Hidden sources of peanut were suspected. The clinician went through a list of relevant "hidden allergen" terms (words used on labeling that may obscure the presence of a substance in a product) and other possible sources of peanuts, and no peanuts were found. But it was determined that the mother was eating pecan nuts once to twice a week. The child would thus also have been exposed through the breast milk.

Could the exposure to pecan nuts increase (or maintain) the child's sensitivity to peanut? No research has yet been done on this, so we do not know. But we do know that cross-reaction between pecan nut and peanut has been previously recorded.

In an investigation of the pecan nut packaging, it was determined that the nuts were in actual fact "Mandalona" nuts, i.e., a manufactured product made from de-flavored, de-colored peanut meal that is pressed into molds, re-flavored and re-colored, and sold as a substitute for tree nuts such as pecan nuts. When this product was excluded from the diet, the symptoms improved again.

It should be noted that there are other causes of eczema (as mentioned above) and that the condition can flare up seasonally, but for the purpose of this newsletter, it has been simplified to only one cause, i.e., peanut allergy. This newsletter will only focus on the aspects that determine and influence the allergenicity of peanuts as well as the different routes that peanut allergic patients come into contact with allergens.

Key lessons from this case study:

  • Peanut allergens can be passed through breast milk to the breastfeeding child.

  • Repeating the serum-specific IgE to the food causing an adverse reaction can indicate whether or not the patient has been avoiding the food effectively.

  • One should always keep in mind unexpected means of contact with peanut in the assessment and management of peanut allergic patients.
TIP for Allergy Advisor users:
Searching for "peanut" under "Items, substances and allergens" brings up the information that peanut allergens can pass through breast milk and cause adverse reactions in infants. From there one can search for cross-reactions with peanut to find that cross-reaction with tree nuts such as pecan nut have been previously recorded. One can also print out a diet sheet for a patient that indicates which foods are allowed and which restricted. This sheet also lists the hidden allergens and informs the patient about medic alert bracelets and treatments that can be carried with a patient and administered on the spot when necessary. The program also warns the user of "Mandalona" nuts as a possible source of peanut.

B. More information:

Peanut-allergic patients are known to have, even at first exposure, more severe symptoms than those with other food allergies. About a third of peanut-sensitive individuals experience severe reactions to peanut.1 The allergy is also known to often induce symptoms on minimal contact.2,3 Severe reactions have been reported even, for example, after contact through intact skin. As little as 100 micrograms of peanut protein has been found to provoke symptoms.4 Children with damaged skin (e.g., eczema) may be particularly sensitive to topically applied medications containing potentially allergenic components, including peanut oils.3 Skin-prick testing and peanut-specific IgE levels do not predict clinical severity.2

Sensitization to peanut
Peanut allergy usually presents after a period of sensitization to peanut. However, some children have severe reactions during their apparent first exposure. Patients could have been previously exposed to minute amounts of the allergen through breast milk, through peanut hidden in foods, or simply because peanut oil is widely used in many consumer products (including infant formulas and Vitamin D preparations).5

Peanut allergy has also increased in prevalence. It is not yet clear whether the increase is a result of the recent rise in atopic diseases, or whether it is because of peanut-specific factors such as increased peanut consumption, use of peanut-containing nonfood products, transfer of peanut through breastfeeding, or other factors. The early introduction of foods with potentially cross-reacting proteins, such as soy or carob, has been implicated, but cross-reactions between these foods are not strong. The presence of panallergens (allergens with similar characteristics that are present in a wide range of plants and foods not related by family) such as lipid transfer protein and profilin may also play a role.6

The possibility of genetic predisposition to peanut allergy has also been suggested.5

Does peanut allergy persist indefinitely?
Peanut allergy raises major concerns and requires diligence in families because of the possibility of severe reactions, the relatively common inability to outgrow peanut allergy, and the widespread availability of peanuts in the Western diet. However, peanut allergy is outgrown in approximately 22% of children, especially in those with histories of only cutaneous reactions and with current low peanut-specific IgE levels. The patients with milder reactions on presentation have a better chance of developing tolerance to peanuts than the patients whose first reaction was anaphylaxis.7,8

Peanut's botanical family

Peanuts are botanically unrelated to nuts that grow on trees. Peanuts are legumes.9 Although other legumes contain similar proteins to those in peanuts, less than 15% of peanut-allergic patients react to other members of the legume family. Other legumes rarely provoke severe anaphylactic reactions or result in a lifelong allergy. Interestingly, 25-35% of peanut-allergic patients may develop an allergic reaction to tree nuts, even though they are from different botanical families.10,11,12

Peanut varieties
Peanuts from different varieties and from different parts of the world are comprised of similar proteins. The IgE binding properties are also similar, and therefore there is no difference in allergenicity between species. This indicates that differences in the serology of peanut allergy might not originate from differences in the allergen composition of the peanut. 13,14

The high-oleic peanut is a new peanut variety developed by the University of Florida and known as SunOleic. It contains approximately 80% oleic acid, compared to 50% oleic acid in normal peanuts. SunOleic has a longer shelf life and lowers cholesterol levels in hypercholesterolemia significantly. There is no difference in allergenicity between normal and high-oleic peanuts.15

Allergens in peanut
A person can have an allergy to one or more of the allergens in peanut. Different percentages of people are allergic to the different allergens.
Various allergens have been isolated:
Ara h 1 (vicilin, a seed storage protein), Ara h 2, Ara h 3, Ara h 4 (a seed storage protein), Ara h 5 (a profilin), Ara h 6 and Ara h 7 (2S albumins).

Ara h 1, Ara h 2 and Ara h 3 are major peanut allergens and have been recognized by IgE from more than 95% of peanut-sensitive individuals. These allergens, in particular Ara h 1, have been shown to be stable to digestion and to survive most food processing methods.16

Other allergens that have been isolated include panallergens such as profilin, lipid transfer proteins, chitinase and 2S albumin as well as sodium salicylates. Whether sodium salicylates result in adverse reactions is controversial.17,18,19

Lipid transfer proteins (LTPs) are heat-stable allergens, but profilin is heat-labile. These allergens cross-react with a broad range of foods.20,21 Due to the extreme resistance of LTP's to pepsin digestion, LTP's in particular are potentially severe food allergens.20The specific problem in a reaction to a panallergen is that such a patient is at risk of cross-reacting to a broad range of foods that are not related by family. Where peanuts are concerned, however, the greater risk is a concominant allergy to tree nuts (which are also not related by family).

Cooking peanuts

The major allergens in peanut are heat-stable, and chemical denaturation appears to reduce their allergenicity only minimally. These allergens can resist gastric acid fluid degradation.22 However, frying or boiling peanuts, as is done in China, appears to affect the allergenicity more than the dry roasting (including the method used for manufacturing peanut butter) practiced widely in the United States. Roasting uses higher temperatures, which apparently increase the allergenicity of the 3 major peanut proteins more than the lower temperatures used for boiling or frying. This may help explain the difference in prevalence of peanut allergy observed in the 2 countries.12,23,24

The protein concentration is approximately 16.6g/100g in raw peanuts, compared to approximately 2.6g/100 g in roasted peanuts indicating potentially more allergenicity.25 Peanut allergens that have undergone the Maillard reaction (this occurs in foods during thermal processing and home cooking and is a nonenzymatic browning reaction between a protein and a reducing sugar) are more resistant to heat and digestion by gastrointestinal enzymes than those that have not. Thus, thermal processing may play an important role in enhancing the allergenic properties of peanuts, and the protein modifications made by the Maillard reaction contribute to this effect.26,27The storage and roasting of peanuts increases the content of other peanut allergens, possibly causing adverse reactions (discussed below).

Products made from peanuts:
Peanuts can be eaten as a vegetable, crushed or ground as a "butter", roasted or salted as snacks, incorporated into candy and used for an oil extracted by solvents or pressure.5

a. Peanut oil:
Peanut oil is obtained from the seed kernels of the plant.28 Highly processed oils (acid-extracted, heat-distilled oils) do not contain peanut protein and can be safely consumed by allergic patients. However, many of the oils on the market undergo minimal processing (i.e. they are cold-pressed or extruded peanut oils, with processing at lower temperatures). These oils (known as crude peanut oil) can contain traces of peanut protein and many induce allergic reactions in 10% of allergic subjects, compared to refined peanut oil, which does not pose any risk.12,29,30 Infant formulas manufactured with peanut oil have been shown to induce adverse reactions.31

Products that are derived from peanut oil include hydrogenated peanut oil, peanut acid and peanut glycerides. Peanut oils and glycerides are used in toiletries and cosmetics such as skin-conditioning agents. (Peanut oil can enhance the absorption of other compounds when applied to the skin.) Peanut oil can be used in creams, soaps, etc. No data on the allergenicity of peanut flour (see below) in cosmetic products is available, but the products are likely to contain peanut allergens.28 Peanut oil is used in many prescribed products, including eczema creams, and in over-the-counter remedies. It may be used in a nipple cream and a breast-feeding baby is likely to consume small amounts.10 Vitamin tablets and drops also sometimes contain traces of peanut oil.10,32

Peanut acid is used in surfactant-cleansing agents. The major allergens in peanuts are not present in these products.28

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