Insect Allergy

Published on 22/03/2015 by admin

Filed under Pediatrics

Last modified 22/04/2025

Print this page

This article have been viewed 1328 times

Chapter 140 Insect Allergy

Scott H. Sicherer, Donald Y.M. Leung

Allergic responses to stinging or, more rarely, biting insects vary from localized cutaneous reactions to systemic anaphylaxis. Allergic reactions that are caused by inhalation of airborne particles of insect origin result in acute and chronic respiratory symptoms of seasonal or perennial rhinitis, conjunctivitis, and asthma.

Etiology

Most reactions to biting and stinging insects, such as those induced by mosquitoes, flies, and fleas, are limited to a primary lesion isolated to the area of the bite and do not represent an allergic response. Occasionally, insect bites or stings induce pronounced localized reactions or systemic reactions that may be based on immediate or delayed hypersensitivity reactions. Systemic allergic responses to insects are attributed most typically to immunoglobulin (Ig) E antibody–mediated responses, which are caused primarily by stings from venomous insects of the order Hymenoptera and more rarely from ticks, spiders, scorpions, and Triatoma (kissing bug). Members of the order Hymenoptera include apids (honeybee, bumblebee), vespids (yellow jacket, wasp, hornet), and formicids (fire and harvester ants) (Fig. 140-1). Among winged stinging insects, yellow jackets are the most notorious for stinging because they are aggressive and ground dwelling, and they linger near activities involving food. Hornets nest in trees, whereas wasps build honeycomb nests in dark areas such as under porches; both are aggressive if disturbed. Honeybees are less aggressive, nest in tree hollows, and, unlike the stings of other flying Hymenoptera, honeybee stings almost always leave a barbed stinger with venom sac.

Figure 140-1 Species of Hymenoptera and their geographical distribution.

(From Freeman TM: Hypersensitivity to Hymenoptera stings, N Engl J Med 351:1978–1984, 2004.)

In the USA, fire ants are found increasingly in the Southeast, living in large mounds of soil. When disturbed, the ants attack in large numbers, anchor themselves to the skin by their mandibles, and sting multiple times in a semicircular pattern. Sterile pustules form at the sting sites. Systemic reactions to stinging insects occur in 0.4-0.8% of children and 3% of adults and account for ≈40 deaths each year in the USA.

IgE antibody–mediated allergic responses to airborne particulate matter carrying insect emanations contribute to seasonal and perennial symptoms affecting the upper and lower airways. Seasonal allergy is attributed to exposures to a variety of insects, particularly aquatic insects such as the caddis fly and midge, or lake fly, at a time when larvae pupate and adult flies are airborne. Perennial allergy is attributed to sensitization to insects such as cockroaches and ladybugs as well as house dust mite, which is phylogenetically related to spiders rather than insects and has eight rather than six legs.

Pathogenesis

Localized skin responses to biting insects are caused primarily by vasoactive or irritant materials derived from insect saliva, and rarely occur from IgE-associated responses. Systemic IgE-mediated allergic reactions to salivary proteins of biting insects such as mosquitoes are reported but uncommon.

Hymenoptera venoms contain numerous components with toxic and pharmacologic activity and with allergenic potential. These constituents include: vasoactive substances such as histamine, acetylcholine, and kinins; enzymes such as phospholipase and hyaluronidase; apamin; melittin; and formic acid. The majority of patients who experience systemic reactions after Hymenoptera stings have IgE-mediated sensitivity to antigenic substances in the venom. Some venom allergens are homologous among members of the Hymenoptera order; others are family specific. There is substantial cross reactivity among vespid venoms, but these venom allergies are distinct from honeybee venom allergies.

A variety of proteins derived from insects can become airborne and induce IgE-mediated respiratory responses, causing inhalant allergies. The primary allergen from the caddis fly is a hemocyanin-like protein, and that from the midge fly is derived from hemoglobin. Allergens from the cockroach are the best studied and are derived from cockroach saliva, secretions, fecal material, and debris from skin casts.

Clinical Manifestations

Insect bites are usually urticarial but may be papular or vesicular. Papular urticaria affecting the lower extremities in children is usually caused by multiple bites. Occasionally, individuals have large local reactions. IgE antibody–associated immediate- and late-phase allergic responses to mosquito bites sometimes mimic cellulitis.

Clinical reactions to stinging venomous insects are categorized as local, large local, generalized cutaneous, systemic, toxic, and delayed/late. Simple local reactions involve limited swelling and pain, and generally last <24 hr. Large local reactions develop over hours and days, involve swelling of extensive areas (>10 cm) that are contiguous with the sting site, and may last for days. Generalized cutaneous reactions typically progress within minutes and include cutaneous symptoms of urticaria, angioedema, and pruritus beyond the site of the sting. Systemic reactions are identical to anaphylaxis from other triggers and may include symptoms of generalized urticaria, laryngeal edema, bronchospasm, and hypotension. Stings from a large number of insects at once may result in toxic reactions of fever, malaise, emesis, and nausea owing to the chemical properties of the venom in large doses. Serum sickness, nephrotic syndrome, vasculitis, neuritis, or encephalopathy may occur as delayed/late reactions to stinging insects.

Inhalant allergy caused by insects results in clinical disease similar to that induced by other inhalant allergens such as pollens. Depending on individual sensitivity and exposure, reactions may result in seasonal or perennial rhinitis, conjunctivitis, and asthma.

Diagnosis

The diagnosis of allergy from biting and stinging insects is generally evident from the history of exposure, typical symptoms, and physical findings. The diagnosis of Hymenoptera allergy rests in part on the identification of venom-specific IgE by prick skin testing. The primary reasons to pursue testing are to confirm reactivity when venom immunotherapy (VIT) is being considered or when it is clinically necessary to confirm venom hypersensitivity as a cause of a reaction. Venoms of five Hymenoptera (honeybee, yellow jacket, yellow hornet, white-faced hornet, and wasp) as well as the jack jumper ant in Australia and whole-body extract of fire ant are available for skin testing. Although skin tests are considered to be the most sensitive modality for detection of venom-specific IgE, additional evaluation with an in vitro serum assay for venom-specific IgE is recommended if skin test results are negative in the presence of a convincing history of a severe systemic reaction. With in vitro tests, there is a 20% incidence of both false-positive and false-negative results, so it is not appropriate to exclude venom hypersensitivity based on this test alone. If initial skin prick and in vitro test results are negative in the context of a convincing history of a severe reaction, repeat testing is recommended before one concludes that allergy is unlikely. Skin tests are usually accurate within 1 wk of a sting reaction, but occasionally a refractory period is observed that warrants retesting after 4-6 wk if the initial results are negative. As many as 40% of skin test–positive subjects may not experience anaphylaxis on sting challenge, so testing without an appropriate clinical history is potentially misleading.

The diagnosis of inhalant insect allergy may be evident from a history of typical symptoms induced seasonally in specific geographic regions. A chronic respiratory symptom during long-term exposure, as may occur with cockroach allergy, is less amenable to identification by history alone. Skin prick or in vitro immunoassay tests for specific IgE to the insect are used to confirm inhalant insect allergy. Allergy tests may be particularly warranted for potential cockroach allergy in patients with persistent asthma and known cockroach exposure.

Treatment

For local cutaneous reactions caused by insect bites and stings, treatment with cold compresses, topical medications to relieve itching, and, occasionally, the use of a systemic antihistamine and oral analgesic are appropriate. Stingers should be removed promptly by scraping, with caution not to squeeze the venom sac because doing so could inject more venom. Sting sites rarely become infected, possibly owing to the antibacterial actions of venom constituents. Vesicles left by fire ant stings that are scratched open should be cleansed to prevent secondary infection.

Anaphylactic reactions after a Hymenoptera sting are treated exactly like anaphylaxis from any cause. Therapies may include oxygen, epinephrine, intravenous saline, steroids, antihistamines, and other treatments (Chapter 143). Referral to an allergist-immunologist should be considered for patients who have experienced a generalized cutaneous or systemic reaction to an insect sting, need education about avoidance and emergency treatment, may be candidates for VIT, or have a condition that may complicate management of anaphylaxis (use of β-blockers).

Venom Immunotherapy

Hymenoptera VIT is highly effective (95-97%) in decreasing the risk for severe anaphylaxis. The selection of patients for VIT depends on several factors (Table 140-1). Individuals with local reactions regardless of age are not at increased risk for severe systemic reactions on a subsequent sting and are not candidates for VIT. The risk of a systemic reaction for those who experienced a large local reaction is no more than 4-10%; testing or VIT is usually not recommended, and prescription of self-injectable epinephrine is considered optional but usually not necessary. Those who experience severe systemic reactions, with airway involvement or hypotension, and have a positive skin test result should receive immunotherapy. Immunotherapy against winged Hymenoptera is not usually indicated for children ≤16 yr of age in whom stings have caused only generalized urticaria or angioedema, because their risk for a reaction after a subsequent sting is <10%, with isolated skin reactions the most likely event. The risk could be reduced to 1% after treatment with VIT, so it is an option to consider if multiple future stings are anticipated. Immunotherapy against Hymenoptera is indicated in those ≥17 yr of age if venom skin test results are positive and there is a history of generalized urticaria or a systemic reaction, because their risk for future systemic reactions is ≈60-70%. VIT is usually not indicated if there is no evidence of IgE to venom. The incidence of adverse effects in the course of treatment is not trivial in adults, as 50% experience large local reactions and about 7% experience systemic reactions. The incidence of both local and systemic reactions is much lower in children. It is uncertain how long immunotherapy with Hymenoptera venom should continue; lifelong treatment has been advocated for patients with very severe reactions. Consideration to discontinue therapy after 3-5 yr has been suggested, however, because >80% of adults who have received 5 yr of therapy tolerate challenge stings without systemic reactions for 5-10 yr after completion of treatment. Long-term responses to treatment are even better for children. Follow-up over a mean of 18 yr of children with moderate to severe insect sting reactions who received VIT for a mean treatment period of 3.5 yr and were stung again showed a reaction rate of only 5%; untreated children experienced a reaction rate of 32%. Whereas duration of therapy with VIT may be individualized, it is clear that a significant number of untreated children retain their allergy.

Table 140-1 INDICATIONS FOR VENOM IMMUNOTHERAPY AGAINST WINGED HYMENOPTERA

Less is known about the natural history of fire ant hypersensitivity and efficacy of immunotherapy for this allergy. The criteria for starting immunotherapy are similar to those for hypersensitivities to other Hymenoptera, but there is stronger consideration to treat children ≤16 yr of age with VIT if they have experienced only generalized urticaria. Only whole-body fire ant extract is commercially available for diagnostic skin testing and immunotherapy.

Inhalant Allergy

The symptoms of inhalant allergy caused by insects are managed as for other causes of seasonal or perennial rhinitis (Chapter 137), conjunctivitis (Chapter 141), and asthma (Chapter 138).

Prevention

Avoidance of stings and bites is essential. To reduce the risk of stings, sensitized individuals should avoid attractants such as perfumes and bright-colored clothing outdoors, wear gloves when gardening, and wear long pants and shoes with socks when walking in the grass or through fields. Typical insect repellents do not guard against Hymenoptera. Nests of these insects should be removed if they are close to the home.

Individuals who have had generalized cutaneous or systemic reactions to Hymenoptera stings should have immediate access to self-injectable epinephrine. Adults responsible for allergic children, and older patients who can self-treat, must be carefully taught the indications for and technique of administration of this medication. Particular attention is necessary for children in out-of-home daycare centers, at school, or attending camps, to ensure that an emergency action plan is in place. The individual at risk for anaphylaxis from an insect sting should also wear an identification bracelet indicating the allergy.

Avoidance of the insect is the preferred management of inhalant allergy. This can prove difficult, particularly, for instance, for those living in multiple-dwelling apartments, where eradication of cockroaches is problematic. Immunotherapy is occasionally undertaken in such cases, but beneficial results have not been thoroughly documented.

Freeman TM. Hypersensitivity to hymenoptera stings. N Engl J Med. 2004;351:1978-1984.

Golden DB. Insect allergy in children. Curr Opin Allergy Clin Immunol. 2006;6:289-293.

Golden DB, Kagey-Sobotka A, Norman PS, et al. Outcomes of allergy to insect stings in children, with and without venom immunotherapy. N Engl J Med. 2004;351:668-674.

Moffitt JE, Golden DB, Reisman RE, et al. Stinging insect hypersensitivity: a practice parameter update. J Allergy Clin Immunol. 2004;114:869-886.

Müller U, Golden DB, Lockey RF. Immunotherapy for hymenoptera venom hypersensitivity. Clin Allergy Immunol. 2008;21:377-392.

Tankersley MS. The stinging impact of the imported fire ant. Curr Opin Allergy Clin Immunol. 2008;8:354-359.

Related

Nelson Textbook of Pediatrics Expert Consult