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Arthropod Bites and Stings
James E. Powers, DO, FACEP, FAAEM
image BASICS
Arthropods make up the largest division of the animal kingdom; two classes, insects and arachnids, have the greatest medical impact on humans. Arthropods affect humans by inoculating poison or irritative substances through a bite or sting, by invading tissue, or by contact allergy to their skin, hairs, or secretions. The greatest medical importance is transmission of infectious microorganisms that may occur during insect feeding. Sequelae to arthropod bites, stings, or contact may include the following:
  • Local redness with itch, pain, and swelling: common, usually immediate and transient
  • Large local reactions increasing over 24 to 48 hours
  • Systemic reactions with anaphylaxis, neurotoxicity, organ damage, or other systemic toxin effects
  • Tissue necrosis or secondary infection
  • Infectious disease transmission: presentation may be delayed weeks to years
  • Difficult to estimate, as most encounters unreported
  • ˜40 deaths per year in the United States from fatal anaphylactic reaction to insects but likely underreported (1)
  • Unrecognized anaphylactic reactions to Hymenoptera stings may be cause of 1/4 of sudden and unexpected deaths outdoors (2).
Widespread, with regional and seasonal variations
  • Arthropods: four medically important classes
    • Insects: Hymenoptera (bees, wasps, hornets, fire ants), mosquitoes, bed bugs, flies, lice, fleas, beetles, caterpillars, and moths
    • Arachnids: spiders, scorpions, mites, and ticks
    • Chilopods (centipedes)
    • Diplopods (millipedes)
  • Four general categories of pathophysiologic effects: toxic, allergic, infectious, and traumatic
    • Toxic effects of venom: local (tissue inflammation or destruction) versus systemic (neurotoxic or organ damage)
    • Allergic: Antigens in saliva may cause local inflammation. Exaggerated immune responses may result in anaphylaxis or serum sickness.
    • Trauma: Mechanical injury from biting or stinging causes pain, swelling, and portal of entry for bacteria and secondary infection. Retention of arthropod parts can cause a granulomatous reaction.
    • Infection: Arthropods are vectors and can transmit bacterial, viral, and protozoal diseases.
Family history of atopy may be a factor in the development of more severe allergic reactions.
  • Previous sensitization is a key to most severe allergic reactions, but exposure history may not be recalled.
  • Although most arthropod contact is inadvertent, certain activities, occupations, and travel increase risk.
  • Greater risk for adverse outcome in young, elderly, immune compromised, or those with unstable cardiac or respiratory status
  • Increased risk of anaphylaxis following insect sting in patients with mastocytosis (1)
  • Avoidance of common arthropod habitats
  • Insect repellents (not effective for bees, spiders, scorpions, caterpillars, bed bugs, fleas, ants)
    • N,N-diethyl-meta-toluamide (DEET)
      • Most effective broad-spectrum repellent against biting arthropods (3)
      • Formulations with higher concentrations (20-50%) are 1st-line choice when visiting areas of endemic arthropod-borne diseases (3).
      • Concentrations >30% give longer duration of effect
      • Safe for children >6 months of age and pregnant and lactating women (3)
    • Icaridin (formerly known as picaridin)
      • Use of concentrations <20% may require more frequent application to maintain effectiveness.
    • P-menthane-3,8-diol (PMD): component of lemon eucalyptus extract
      • Recommended alternative repellent to DEET at concentrations >20% (3)
      • May be used in children >6 months of age (3)
    • IR3535: less effective in most studies
    • Other botanical oils (citronella etc.): less effective than DEET; not for disease-endemic areas
  • Barrier methods: clothing, bed nets
    • Use of light-colored pants, long-sleeved shirts, and hats may reduce arthropod impact.
    • Permethrin: Synthetic insecticide derived from chrysanthemum plant should not be applied to skin, but permethrin-impregnated clothing provides good protection against arthropods.
    • Mosquito nets: Insecticide-treated nets are advised for all travelers to disease-endemic areas at risk from biting arthropods (3).
    • WHO-recommended nets are Permanet 2.0 (Vestergaard), Olyset (Sumitomo), and Interceptor (BASF) (3).
  • Desensitization 75-95% effective for Hymenoptera-specific venom
    • Skin tests are needed to determine sensitivity.
    • Refer to allergist/immunologist if candidate
  • Fire ant control (but not elimination) possible
    • Baits; sprays, dusts, aerosols; biologic agents
  • Risk of tick-borne diseases decreased by prompt removal of ticks within 24 hours of attachment.
  • If stinger is still present in skin, remove by flicking or scraping away from skin.
  • Anaphylaxis is a clinical diagnosis. Essential to examine for signs and symptoms of anaphylaxis (4,5)
    • Erythema, urticaria, angioedema
    • Itching/edema of lips, tongue, uvula; drooling
    • Persistent vomiting
    • Respiratory distress, wheeze, repetitive cough, stridor, dysphonia
    • Hypotension, dysrhythmia, syncope, chest pain
  • If anaphylaxis not present, exam focuses on the sting or bite itself. Common findings include local erythema, swelling, wheals, urticaria, papules, or bullae; excoriations from scratching.
  • Thorough exam to look for arthropod infestation (lice, scabies) or attached ticks. Body lice usually found in seams of clothing. Skin scraping to identify scabies.
  • Signs of secondary bacterial infection after 24 to 48 hours: increasing erythema, pain, fever, lymphangitis, or abscess
  • Delayed manifestations of insect-borne diseases
  • Urticaria and localized dermatologic manifestations:
    • Contact dermatitis, drug eruption, mastocytosis, bullous diseases, dermatitis herpetiformis, tinea, eczema, vasculitis, pityriasis, erythema multiforme, viral exanthem, cellulitis, abscess, impetigo, folliculitis, erysipelas, necrotizing fasciitis
  • Anaphylactic-type reactions
    • Cardiac, hemorrhagic, or septic shock; acute respiratory failure, asthma; angioedema, urticarial vasculitis; flushing syndromes (catecholamines, vasoactive peptides); panic attacks, syncope
    • Differential diagnosis of the acute abdomen should include black widow spider bite.
Initial Tests (lab, imaging)
Seldom needed; basic lab parameters usually normal. Some findings may help confirm diagnosis of anaphylaxis:
  • Plasma histamine levels elevated briefly after mast cell activation
  • Serum tryptase within 15 minutes to 3 hours after onset of symptoms with second sample 24 hours later (5)
Follow-Up Tests & Special Considerations
  • Severe envenomations may affect organ function and require monitoring of lab values (CBC, comprehensive metabolic panel, prothrombin time/international normalized ratio)
  • Labs for arthropod-borne diseases, as indicated
    • Ticks: Lyme disease, Rocky Mountain spotted fever, relapsing fever, anaplasmosis, babesiosis, tularemia
    • Flies: tularemia, leishmaniasis, African trypanosomiasis, bartonellosis, loiasis
    • Fleas: plague, tularemia, murine typhus
    • Chigger mites: scrub typhus
    • Body lice: epidemic typhus, relapsing fever
    • Kissing bugs: Chagas disease
    • Mosquitoes: malaria, yellow fever, dengue fever, West Nile virus, equine encephalitis, chikungunya
  • Refer to allergist for formal testing with history of anaphylaxis, significant systemic symptoms, progressively severe reactions (4,5)
Diagnostic Procedures/Other
Various skin tests and immunologic tests available to try to predict anaphylactic risk

Local wound care, ice compress, elevation, analgesics
First Line
  • For arthropod bites/stings with anaphylaxis
    • There are no randomized controlled trials on treatments, so the following recommendations are all based on expert opinion consensus (5)[C].
    • Epinephrine: most important: IM injection in midanterolateral thigh (vastus lateralis muscle):
      • IM injection: epinephrine 1:1,000 (1 mg/mL): adult: 0.3 to 0.5 mg per dose; pediatric: give 0.01 mg/kg to a maximum dose of 0.5 mg per dose, can repeat every 5 to 15 minutes (5)
    • Positioning: supine with legs elevated
    • Oxygen 6 to 8 L/min up to 100%, as needed
    • IV fluids: Establish 1 to 2 large-bore IV lines. Normal saline rapid bolus 1 to 2 L IV; repeat as needed (pediatrics 20 to 30 mL/kg)
    • H1 antihistamines: diphenhydramine 25 to 50 mg IV (pediatrics 1 to 2 mg/kg)
    • β2 agonists: albuterol for bronchospasm nebulized 2.5 to 5 mg in 3 mL
    • Emergency treatment of refractory cases: consider epinephrine infusion, dopamine, glucagon, vasopressin, large-volume crystalloids (4,5)
  • Arthropod bites/stings without anaphylaxis
    • Tetanus booster, as indicated
    • Oral antihistamines
      • Diphenhydramine
      • Cetirizine
      • H2 blockers: ranitidine
    • Oral steroids: consider short course for severe pruritus; prednisone or prednisolone 1 to 2 mg/kg once daily
    • Topical intermediate-potency steroid cream or ointment × 3 to 5 days
      • Desoximetasone 0.05%
      • Triamcinolone 0.1%
      • Fluocinolone 0.025%
    • Wound care: antibiotics only if infection
    • Other specific therapies:
      • Scorpion stings: Treat excess catecholamine release (nitroprusside, prazosin, β-blockers). Diazepam for muscle spasms. Atropine for hypersalivation (6). Only one FDA-approved scorpion antivenom in United States and should be administered in conjunction with toxicologist. Black widow bites: Treat muscle spasms with diazepam and opioid analgesics PO or IV (6). Antivenom: available but should be administered in conjunction with toxicologist.
      • Poison control should be consulted for questions regarding management of envenomation. Poison Control hotline: 1-800-222-1222.
    • Fire ants: characteristically cause sterile pustules. Leave intact: Do not open or drain.
    • Brown recluse spider: pain control, supportive treatment; surgical consult if débridement needed
    • Ticks: early removal. Review guidelines for disease prophylaxis and treatment.
    • Pediculosis: head, pubic, and body lice
      • First line: permethrin 1% (Nix) topical lotion. Apply to affected area, wash off in 10 minutes.
      • Alternatives: pyrethrin or malathion 0.5% lotion, ivermectin (not FDA approved for pediculosis) orally
      • Repeat above treatment in 7 to 10 days.
      • For eyelash infestation: Apply ophthalmic-grade petroleum jelly BID for 10 days.
    • Sarcoptes scabiei scabies
      • Permethrin 5% cream: Apply to entire body. Wash off after 8 to 14 hours. Repeat in 1 week.
      • Ivermectin: 200 µg/kg PO once; repeat in 2 weeks (not FDA approved for this use)
      • Crotamiton 10% cream or lotion less efficacious; apply daily for 2 days after bathing.
Second Line
Second-line options for anaphylaxis:
  • Ranitidine
  • Methylprednisolone 1 mg/kg for 3 to 4 days or hydrocortisone 200 mg (5)
Refer to allergist with history of anaphylaxis, severe systemic symptoms, or progressively severe reactions
Débridement and delayed skin grafting may be needed for brown recluse spider and other bites.
  • Some stings may be treated with a paste of 3 tsp of baking soda and 1 tsp water.
  • None well tested
Admission Criteria/Initial Stabilization
Anaphylaxis, vascular instability, neuromuscular events, pain, GI symptoms, renal damage/failure
  • Immunotherapy as recommended by allergist/consultant for anaphylaxis or serious reactions; venom immunotherapy cornerstone of treatment for Hymenoptera.
  • Patient-administered epinephrine must be provided to patients with anaphylaxis. Consider “med-alert” identifiers (4,5).
Patient Monitoring
  • Monitor for delayed effects, including infectious diseases from arthropod vectors.
  • Serum sickness reactions, vasculitis (rare)
Avoidance and prevention
  • Excellent for local reactions
  • For systemic reactions, best response with early intervention to prevent cardiorespiratory collapse
1. Tanskersley MS, Ledford DK. Stinging insect allergy: state of the art 2015. J Allergy Clin Immunol Pract. 2015;3(3):315-322.
2. Diaz JH. Recognition, management, and prevention of hymenopteran stings and allergic reactions in travelers. J Travel Med. 2009;16(5):357-364.
3. Moore SJ, Mordue Luntz AJ, Logan JG. Insect bite prevention. Infect Dis Clin North Am. 2012;26(3): 655-673.
4. Simons FE, Ardusso LR, Bilò MB, et al. 2012 update: World Allergy Organization guidelines for the assessment and management of anaphylaxis. Curr Opin Allergy Clin Immunol. 2012;12(4):389-399.
5. De Bisschop MB, Bellou A. Anaphylaxis. Curr Opin Crit Care. 2012;18(4):308-317.
6. Quan D. North American poisonous bites and stings. Crit Care Clin. 2012;28(4):633-659.
Additional Reading
  • Centers for Disease Control and Prevention. Protection against mosquitoes, ticks, & other insects & arthropods. http://wwwnc.cdc.gov/travel/yellowbook/2014/chapter-2-the-pre-travel-consultation/protection-against-mosquitoes-ticks-and-other-insects-and-arthropods. Accessed 2015.
  • Centers for Disease and Prevention. FAQ. Insect repellent use & safety. http://www.cdc.gov/westnile/faq/repellent.html. Accessed 2015.
  • Centers for Disease Control and Prevention. Tickborne diseases of the United States: a reference manual for health care providers. Third edition, 2015. Handbook available as a PDF at http://www.cdc.gov/ticks/
  • Sicherer SH, Leung DY. Advances in allergic skin disease, anaphylaxis, and hypersensitivity reactions to foods, drugs, and insects in 2012. J Allergy Clin Immunol. 2013;131(1):55-66.
  • Studdiford JS, Conniff KM, Trayes KP, et al. Bedbug infestation. Am Fam Physician. 2012;86(7): 653-658.
  • Swanson DL, Vetter RS. Bites of brown recluse spiders and suspected necrotic arachnidism. N Engl J Med. 2005;352(7):700-707.
  • Warrell DA. Venomous bites, stings, and poisoning. Infect Dis Clin North Am. 2012;26(2):207-223.
  • Juckett G. Arthropod bites. Am Fam Physician. 2013; 88(12):841-847.
  • T63.481A Toxic effect of venom of arthropod, accidental, init
  • T63.301A Toxic effect of unsp spider venom, accidental, init
  • T63.484A Toxic effect of venom of oth arthropod, undetermined, init
Clinical Pearls
  • Urgent administration of epinephrine is a key to anaphylaxis treatment.
  • Local treatment and symptom management are sufficient in most insect bites and stings.