Although many insect bites and stings are simply a nuisance, some patients can have severe skin or systemic reactions. Vespids (yellow jackets, hornets, and wasps), bees (honeybees and bumblebees), and ants inject venom with a stinger. The sting results in immunoglobulin E–mediated systemic reactions that cause the release of mediators (histamines, the slow-reacting substance of anaphylaxis, and eosinophil chemotactic factors of anaphylaxis)¹ from mast cells, culminating in local inflammation involving many cell types and numerous mechanisms.²

These stings induce local, toxic, systemic, and delayed reactions. A local reaction consists of erythema, edema, and pruritus at the sting site. A toxic reaction is initially seen as gastrointestinal distress, lightheadedness, syncope, headache, fever, drowsiness, muscle spasms, edema, and occasionally seizures. A systemic reaction is anaphylaxis, which initially manifests as itchy eyes, facial flushing, generalized urticaria, and dry cough. Anaphylaxis can quickly intensify to respiratory distress, and it may deteriorate to respiratory or cardiovascular failure. A delayed reaction can occur 10 to 14 days after the sting and cause fever, malaise, headache, urticaria, lymphadenopathy, polyarthritis, or more systemic autoimmune illnesses (i.e., leukocytoclastic vasculitis or Henoch-Schönlein purpura).² Table 26-1 describes the pathophysiology and clinical presentation of other insect bites and stings.

Adults with systemic allergic reactions should be considered for venom immunotherapy, which is successful in virtually all patients. The diagnosis of insect sting allergy can be made on the basis of a history of anaphylaxis with a sting and/or positive skin test results.¹ Otherwise, no specific laboratory evaluation is required unless it is indicated by the clinical course.

Differential Diagnosis

The diagnosis of all insect bites and stings is made by obtaining a careful history. It is helpful if the patient brings in the insect. Insect bites are commonly confused with contact dermatitis and viral exanthems. Flea bites may resemble varicella. Reactions to blister beetles may resemble bullous impetigo and burns. Because of such similarities, a history of exposure may be the only diagnostic clue.³

The management of all insect bites and stings begins with local wound care, including removal of the stinger and the use of ice packs, antihistamines (H₁ and H₂ blockers) for itching, topical steroids for inflammation, topical or systemic antibiotics for secondary infection, and nonsteroidal anti-inflammatory drugs to relieve discomfort.³ Any evidence of a systemic reaction must be treated as anaphylaxis.

Management also includes eradication of the insect. For flea infestation, it is necessary to vacuum thoroughly, treat pets, wash the rugs and beds, and use an insecticide. Lice and scabies are eradicated by applying 1% lindane lotion or shampoo (Kwell, Scabene) on two consecutive nights. Permethrin (Nix, Elimite) is another effective scabies treatment. Long-standing or crusted scabies infestation may require oral Ivermectin.

Bedbugs have become an increasingly prevalent problem in institutional settings including dormitories, assisted-living and nursing home facilities, and hotels. These pests are difficult to eradicate and travel easily, “hitching” rides in suitcases and sleeping bags. Although their bites do not carry disease and often go unnoticed, they can cause significant psychological and economic distress.⁴

Ticks are effectively removed with blunt, angled, medium-tipped forceps or a specific tick-removal instrument. The tick should be removed as soon as possible by grasping it close to the mouth, flipping the tick so the backside is closest to the skin, and pulling the tick straight up.⁵ After removal of the tick, the health care provider should inspect the bite area for retained mouth parts, remove if possible, then carefully clean the area with an antiseptic.⁵ Antibiotic prophylaxis may be indicated where Lyme disease is endemic or if the length of time the tick has been imbedded is not known. A tick needs to be embedded and feeding for more than 36 hours to infect with Lyme disease (see Chapter 234).

Disposition and Referral

Systemic reactions to bites and stings may be life-threatening. Thus, any systemic or anaphylactic reaction requires a refer­ral to the emergency department for definitive manage­ment including epinephrine and antihistamines and possible hospitalization.

Prevention and Patient Education

Preventive management against bites and stings includes avoidance and protective clothing. Repellents can be used, including diethyltoluamide (DEET), dimethyl phthalate, dimethyl carbate, ethyl hexanediol, butopyronoxyl (Indalone), and benzyl benzoate.⁶ Any person with a history of anaphylaxis from wasp or bee stings should be given medical warning tags, epinephrine injector kits, and a referral to an allergist or immunologist for venom immunotherapy.^1,7,8

Bedbugs are becoming a more serious problem worldwide, probably because of increasing global travel and resistance to insecticides. Bedbugs are not known to carry any pathogen but cause significant emotional and psychological distress, qualifying them as serious pests. Sleeplessness is a common problem for people in known infested settings. Because bedbugs are visible, travelers should be advised to look for them in the crevices of mattresses, behind headboards, and in the folds of bed linens and curtains. Luggage should be thoroughly vacuumed and cleaned if it is suspected of being infested. Clothing and bed linens are washed in hot water and dried on the hottest setting the fabric can withstand to eradicate the bedbugs. Serious infestations should be managed by professional exterminators.⁴

Pathophysiology and Clinical Presentation

The venom of the brown recluse spider is chemotactic, which results in endothelial injury and subsequent thrombosis.⁹ It is a neurotoxin that causes the release of acetylcholine and norepinephrine at the neurosynaptic junction.² The bite of the brown recluse spider is almost painless and most commonly manifests as a mild, erythematous lesion that may become firm and then heal during several days to weeks. The bite can also be more severe, causing erythema, blistering, and a bluish discoloration within 24 hours and possibly becoming necrotic within 3 to 4 days. The lesions can vary in size from 1 to 30 cm and take 6 weeks to 4 months to heal. The victim may have a systemic response and experience fevers, chills, nausea, vomiting, myalgia, arthralgia, petechiae, hemolysis, or seizures within 24 to 48 hours of the bite. Severe systemic manifestations can lead to hemoglobinuria, renal failure, disseminated intravascular coagulation, and death.⁹

The bite of the black widow spider is mildly to moderately painful; erythema, swelling, and muscle cramps begin at the site within 30 minutes to 12 hours. The muscle cramping progresses to large muscle groups and the abdomen and can mimic peritonitis. The muscle pain can subside in a few hours but can flare during the following 2 to 3 days, with muscle weakness and intermittent spasms persisting for weeks to months. Hypertension can be a serious complication. Anxiety or confusion can also occur. Severe envenomation may lead to shock, coma, or respiratory failure secondary to muscle paralysis. The bite is fatal only to small children or frail elders.⁹