Arthropod Bites and Stings
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- Arthropods are the largest division of the animal kingdom. Two classes, insects and arachnids, have the greatest impact on human health.
- Arthropods affect humans by inoculating poison, microorganisms, or irritative substances through a bite or sting; by invading tissue, or by contact allergy to their skin, hairs, or secretions.
- Transmission of infectious microorganisms during feeding is of the greatest concern.
- Sequelae of bites, stings, or contact include:
- Local redness with itch, pain, and swelling: common, usually immediate and transient
- Large local reactions that increase 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.
28,087 cases of arthropod exposures were reported in 2015. This is a small fraction of arthropod encounters.
Widespread, with regional and seasonal variations
Etiology and Pathophysiology
- 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 or venom 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 transmit bacterial, viral, and protozoal diseases.
Family history of atopy may be a factor in the development of more severe allergic reactions.
- Previous sensitization
- Although most arthropod contact is inadvertent, certain activities, occupations, and travel exposures increase risk.
- Greater risk for adverse outcome in young, elderly, immunocompromised, and those with chronic or poorly controlled cardiac or respiratory disease
- Increased risk of anaphylaxis in patients with mastocytosis
- Avoid 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 (1,2)[A]
- Formulations with higher concentrations (20–50%) are first-line choice in areas of endemic arthropod-borne diseases (2)[A].
- Concentrations >30% have longer duration of action.
- Safe for children >6 months of age and pregnant and lactating women (2)[B]
- Icaridin (formerly known as picaridin)
- P-menthane-3,8-diol (PMD; lemon eucalyptus extract)
- IR3535: less effective in most studies; not appropriate for malaria-endemic regions (1)[B]
- N,N-diethyl-meta-toluamide (DEET)
- 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. Do not apply directly to skin. Permethrin-impregnated clothing provides good protection against arthropods.
- Mosquito nets: advised for all travelers to disease-endemic areas at risk from biting arthropods. Permethrin-treated nets may offer additional protection (2)[B].
- Desensitization 75–95% effective for Hymenoptera-specific venom
- Skin tests to determine sensitivity
- Refer to allergist/immunologist.
- Fire ant control (but not elimination) possible
- Baits; sprays, dusts, aerosols; biologic agents
- Risk of tick-borne diseases may be decreased by prompt removal of ticks within 24 hours of attachment.