Significations et usages de Peanut_allergy

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Peanut allergy
Classification and external resources
A peanut allergy warning
ICD-10	T78.4
ICD-9	995.61, V15.01
DiseasesDB	29154
MeSH	D021183

Peanut allergy is a type of food allergy distinct from nut allergies. It is a type 1 hypersensitivity reaction to dietary substances from peanuts causing an overreaction of the immune system which in a small percentage of people may lead to severe physical symptoms. It is estimated to affect 0.4-0.6% of the population.^[1] In England, an estimated 4,000 people are newly diagnosed with peanut allergy per year (11 per day); 25,700 having been diagnosed with peanut allergy by a clinician at some point in their lives.^[2]

The most severe allergies in general can result in anaphylaxis,^[3] an emergency situation requiring immediate attention and treatment with epinephrine.

It is usually treated with an exclusion diet and vigilant avoidance of foods that may contain whole peanuts or peanut particles and/or oils.

  Symptoms

Symptoms of peanut allergy are related to the action of Immunoglobulin E (IgE) and other anaphylatoxins, which act to release histamine and other mediator substances from mast cells (degranulation). In addition to other effects, histamine induces vasodilation of arterioles and constriction of bronchioles in the lungs, also known as bronchospasm (constriction of the airways).

Symptoms can include the following:^[4]

• vomiting
• diarrhea
• urticaria (hives)
• angioedema (swelling of the lips, face, throat and skin)
• acute abdominal pain
• exacerbation of atopic eczema
• asthma
• anaphylactic shock

The British Dietetic Association warns that: "If untreated, anaphylactic shock can result in death due to obstruction of the upper or lower airway (bronchospasm) or hypotension and heart failure. This happens within minutes to hours of eating the peanuts. The first symptoms may include sneezing and a tingling sensation on the lips, tongue and throat followed by pallor, feeling unwell, warm and light headed. Severe reactions may return after an apparent resolution of 1–6 hours. Asthmatics with peanut sensitivity are more likely to develop life threatening reactions".^[4]

  Causes

The exact cause of someone developing a peanut allergy is unknown. A 2003 study found no link to maternal exposure to peanuts during pregnancy or during breast-feeding,^[5] though the data show a linkage to the amount of time a child is breastfed. The same study indicated that exposure to soy milk or soy products was correlated with peanut allergies. However, an analysis of a larger group in Australia found no linkage to consumption of soy milk, and that the appearance of linkage is likely due to preference to using soy milk among families with known milk allergies.^[6] It's possible that exposure to peanut oils in lotions may be implicated with development of the allergy.^[7][8] Another hypothesis for the increase in peanut allergies (and other immune and auto-immune disorders) in recent decades is the hygiene hypothesis. Comparative studies have found that delaying introduction of peanut products significantly increases the risks of development of peanut allergies,^[9][10] and the American Academy of Pediatrics, in response to ongoing studies that showed no reduction in risk of atopic disease, rescinded their recommendation to delay exposure to peanuts along with other foods. They also found no reason to avoid peanuts during pregnancy or while breastfeeding.^[11] A study conducted jointly in Israel and United Kingdom in 8600 children noted a nearly 10 fold increase in incidence of peanut allergy among U.K. children compared to Israeli children. It was found that Israeli children were given peanuts at a much younger age than those in the U.K. following recommendation of pediatricians in the U.K.^[12] Pediatric Associations in Britain and Australia recommend delaying introduction until age 3 and have not changed their recommendations as of March 2009^[update].^{[citation needed]}

  Prevalence

The Asthma and Allergy Foundation of America estimates that peanut allergy is one of the most common causes of food-related death.^[13] However, there is an increasing body of medical opinion that, while there definitely are food sensitivities, the dramatic rise in frequency of nut allergies and more particularly the measures taken in response to the threat show elements of mass psychogenic illness, hysterical reactions grossly out of proportion to the level of danger:^[14] "Dr. Christakis points out that about 3.3 million Americans are allergic to nuts, and even more — 6.9 million — are allergic to seafood. But of 30 million hospitalizations each year, just 2,000 are due to food allergies, and about 150 people die annually from serious allergic food reactions. That’s the same number of people killed by bee stings and lightning strikes combined. About 10,000 children are hospitalized annually with traumatic brain injuries from sports, 2,000 children drown each year, and about 1,300 die in gun accidents, he writes." Media sensationalism has also been blamed.^[15]

Prevalence among adults and children is similar—around 1%—but at least one study shows it to be on the rise in children in the United States.^[16] The number of young children affected doubled between 1997 and 2002.^[17] 25% of children with a peanut allergy outgrow it.^[18] In America, about 10 people per year die from peanut allergies.^[19]

One study has shown that peanut allergies also correlate with ethnicity; in particular, Native Americans are less prone to be allergic to peanuts.^[20]

  Routes of Exposure

While the most obvious and dangerous route for an allergic individual is unintentional ingestion, some reactions are possible through external exposure. However some of these are controversial, exaggerated, or have been discredited through empirical testing. Common beliefs are that anaphylaxis can be triggered by touching peanuts or products, smelling the odor of peanuts, and simple proximity to peanut products. Many of these beliefs have resulted in controversial bans on all peanut products from entire facilities such as schools and medical facilities. Harvard pediatrician Dr. Michael C. Young notes in his book The Peanut Allergy Answer Book that while such secondary contact might pose a risk to an allergic individual, the occurrence of a reaction is rare and limited to minor symptoms.^[21] Some reactions have been noted to be psychogenic in nature, the result of conditioning and belief rather than a true chemical reaction. Blinded, placebo-controlled studies by Sicherer et al. were unable to produce any reactions using the odor of peanut butter or its mere proximity.^[21] That said, some activities such as cooking or large-scale shelling or crushing of peanuts (such as in a farming or factory production environment) can cause particles to become airborne, and can have respiratory effects to allergic individuals who are nearby. Similarly, residue on surfaces has been known to cause minor skin rashes, though not anaphylaxis.^[21]

  Treatments

Currently there is no confirmed treatment to prevent or cure allergic reactions to peanuts; however some children have been recently participating in a method of treating the allergy to peanuts using mithridatism. This method consists of feeding the children minuscule peanut traces which gradually become larger and larger in order to desensitize the immune system to the peanut allergens.^[17] Strict avoidance of peanuts is the only way to avoid an allergic reaction. Children and adults are advised to carry epinephrine injectors to treat anaphylaxis.

In order to diagnose allergies one must be prepared to first tell their doctor about their symptoms. These symptoms should include any time intervals between the ingestion of the product and the time that the symptoms began. A person should also include the exact type of symptoms and any other history of the symptoms that may have also occurred from this same product. The time interval from the person's last reaction will also be helpful to the doctor to determine the specific allergy or medical issue. One of the first and easiest ways a doctor is able to diagnose the food allergy is by means of something called a Food Challenge. During this challenge, the patient will be asked to eliminate the peanut allergen completely from their diet for a time span from 10 to 14 days from start to finish. This type of elimination food challenge time span if for the IgE mediated allergy. There will be a time span as long as 8 weeks for the reaction called the cell mediated allergic reaction. By running these Food Challenges, doctors are able to determine whether or not the suspicion of the peanut allergy is accurate. The doctor will look at the results after the given time and if the symptoms have not changed, even after the peanuts have been eliminated completely for such a long period of time, that the allergy is probably not the likely cause. If the symptoms go away after the challenge then the allergy is probably the cause of the symptoms.

While several companies have developed promising drugs to counteract peanut allergies, trials have been mired in legal battles.^[22]

  Injected peanut desensitization

An early trial of injecting escalating doses of peanut allergen was conducted in 1996. However, one participant died seconds later from laryngospasm due to a pharmacy error in calculating the dose. The tragic incident itself abruptly ended one of the only studies on injected allergen desensitization to peanut allergies.^[23][24][25]

  Oral desensitization

A desensitization study at Duke University was done with escalating doses of peanut protein. Eight children with known peanut allergy were given escalating doses of peanut protein in the form of a ground flour mixed into apple sauce or other food. To enter the study peanut IgE level > 7 kU/L and a positive skin prick test. The first day, they are given 0.1 mg of peanut protein, then the amount of peanut is increased gradually to 50 mg, if tolerated, over that first day. About ½ of the children tolerated 50 mg dose by the end of the day, while the others were able to reach 12.5 mg or 25 mg. The children continued taking daily doses of peanut at home, returning to the hospital every two weeks for dose increases until they reached 300 mg peanut protein a day, or the equivalent of a single peanut. The maintenance phase follows lasted up to 18 months, depending on how much peanut protein the child tolerated. Seven children completed the study. These children were given a "food challenge" to peanut flour, exposing them to up to nearly 8 grams, or the equivalent of more than 13 peanuts. Five of the seven children tolerated the equivalent of 13 peanuts at the food challenge at the end of the study.^[26] The children’s immunologic findings were similar to those seen with other types of immunotherapy—an initial rise followed by a decline in peanut-specific IgE and IgG. They also had a rise in peanut-specific IgG4 throughout the study, which is thought to be a marker of protection in other forms of immunotherapy.^[27]

In February 2009 a successful desensitization study was announced by Addenbrooke's Hospital in Cambridge, England.^[28] An example of the oral rush immunotherapy protocol is the administration of diluted peanut at a dose of 0.1 mg (1 mL of a 1 gram/10L solution), and escalating by 10 fold every 30 minutes. Once a maximum dose of 50 mg is reached (1 mL of a 5 gram/100 mL solution), or when systemic or local reaction occurs, the escalation is stopped.^[23][29] The patient is maintained on this maximum day one dose daily and the dose is escalated by a less rapid twofold increase each week, or each month, depending on tolerance or protocol used. Reactions are treated with antihistamines, and if needed anaphylactic drugs. Standard protocols are being developed by several clinical trials being conducted in the United States.^[30] Pre- and post-study serum anti-peanut IgE levels are measured, and varying doses and escalation schedules are being compared to placebo in blinded study protocols. Actual desensitization treatments are being carried out in the community using modified protocols.^[31] Success has been reported in both rapid (short duration of weeks) to slow rush protocol (spread over months) with minimal systemic reactions. The first day of the protocol often required inpatient hospital admission, or observation in a physician's office equipped with resuscitative drugs and with IV access). Frequent follow up is required during the desensitization trials to treat reactions and modify the protocol if needed.^[32] Because of the relative safety of oral rush immunotherapy, some in the medical community have questioned if desensitization is better than living with peanut allergy.^[33]

  Allergen-free peanuts

On July 20, 2007, the North Carolina Agricultural and Technical State University announced that one of its scientists, Dr. Mohamed Ahmedna, had developed a process to make allergen-free peanuts. Initial testing showed a 100 percent deactivation of peanut allergens in whole roasted kernels, and human serums from severely allergic individuals showed no reaction when exposed to the processed peanuts. Food companies have expressed an interest in licensing the process, which purportedly does not degrade the taste or quality of treated peanuts, and even results in easier processing to use as an ingredient in food products.^[34]

  References

  External links

• The "Peanut Patch": The future of peanut allergy treatments?
• "Are Nut Bans Promoting Hysteria?" by Tara Parker-Pope at The New York Times (15 Dec 2008)
• This allergies hysteria is just nuts by Nicholas A. Christakis (British Medical Journal, December 2008)
• Peanut Allergy (Finnish)
• Mayo Clinic's Peanut Allergy information
• PeanutAllergy.com is a site for information and support networking of those with peanut allergies
• Peanut allergy information from the Food Allergy & Anaphylaxis Network
• "Peanut Allergy Overview". WebMD. http://www.webmd.com/allergies/tc/peanut-allergy-overview. 
• Allergy Aware.org. "Peanut Allergy". 2009. Web, 20 July 2011.
• Goodman, Brenda (20 June 2011). "Food Allergies in Kids More Common Than Thought". WebMD Health News. http://children.webmd.com/news/20110620/food-allergies-in-kids-more-common-than-thought. Retrieved 2 July 2011. 
• Laino, Charlene (16 March 2009). "New Therapy May Knock Out Peanut Allergy". Web MD. http://www.webmd.com/allergies/news/20090316/new-therapy-may-knock-out-peanut-allergy. Retrieved 31 July 2011.