Hymenoptera Anaphylaxis - ReviewWe thank Dr. E.A. Varga for contributing this article on "wasp" stings. Dr. Varga has been a practicing allergist for 30 years and has extensive expertise in this area. As an expert, his comments are considered Level 4 Evidence. The order Hymenoptera has three families that are of medical importance: Apidae (honey bee, and bumble bee), Vespidae (sub family Polistine - wasps and the subfamily Vespinae includes the yellow jacket, yellow hornet, white-faced hornet) and the imported fire ants - Formicidae. There is considerable cross reactivity of the venoms within these families. The medical treatment of hymenoptera sensitivity has become more straight foreword since the realization by Loveless that the problem was the venom, which is injected by the insect during a sting. A person requires a sting and then over at least two weeks the individual will build up a tolerance to the insect or possibly an allergy to the venom. On occasion frequent or multiple stings may sensitize an individual to create an anaphylactic reaction with the next sting. The incidence of an anaphylactic reaction to a sting is probably about 0.5% from reported cases. From the USA registry there are at least 40 deaths reported/year from stings. An anaphylactic reaction can vary depending on the sensitivity, but will include some of the following symptoms: - coughing, wheezing, shortness of breathe, difficulty in swallowing, abdominal cramps sometimes with diarrhea, incontinence, and a 'feeling of impending doom' described by patients. Patients maybe in shock from hypotension. This may lead to other complications in elderly patient such as strokes and/or heart attacks. Generalized hives may also develop. Venom is a histamine liberator. In patients <20 years (mostly children) it is not uncommon to get generalized hives with no other manifestations. These individuals do not require testing or further treatment. Large numbers have been followed where they have been stung again by the same insect with few if any hives. None have had worsening of the reaction or have had an anaphylactic reaction with another sting by the same insect. About 10% of individuals tested with venom will show a positive reaction. This means that they have circulating antibodies to the venom but does not mean they will have a systemic reaction with the next sting. Treatment with an antihistamine likely will be all that is required. In an acute anaphylactic reaction the only life saving treatment is the use of adrenalin. With a severe reaction use adrenalin and subsequently let an allergist familiar with the problem sort out the long-term management. A radioallergosorbent test (RAST) may be ordered which give the physician a quantitative result as to the degree of sensitivity of the patient. If one orders a RAST for Honeybee, yellow jacket and wasp, it measures specifically for these insects. It is not as sensitive as the skin tests but will give an indication if the patient is at risk. As an Allergist I rarely see anyone with an acute anaphylactic reaction. More commonly the patient has had a recent anaphylactic reaction treated in the emergency room or by the family physician, days or months previously. Most but not all have been prescribed an Epi Pen - Epi Pen Jr for those <40lb (~20Kg) and Epi Pen for those >20Kg. In most cases it is the pharmacist who has instructed the individual in its use. The patient is given a brochure produced by the American Allergy Asthma and Immunology Academy and explained steps taken with future stings. There is no "one" regime for desensitization. The dose and frequency of injections will vary from allergist to allergist and will also depend on the patient's reaction to the treatment. Until recently treatment was stopped after 5 years. New information now suggests that about 4% of patients/year will reactivate. The decision to continue treatment indefinitely depends on the age of the patient, his/her life style and the patient's wishes. Thanks to Dr. Sandeep Kapur for reviewing the draft copy of this article. Dr. Kapur is an Allergist on staff at the IWKGrace Hospital for Children in Halifax, Nova Scotia. References:
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