Arthropod Bites and Stings

Description

• Arthropods are the largest division of the animal kingdom. Two classes, insects and arachnids, have the greatest impact on human disease.
• 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.
• Transmission of infectious microorganisms during feeding is of the greatest concern.
• Sequelae of bites, stings, or contact may include:
  • 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.

Epidemiology

• ~40 deaths per year in the United States from fatal anaphylactic reaction to insects but likely underreported
• Unrecognized anaphylactic reactions to Hymenoptera stings may be cause of 1/4 of sudden and unexpected deaths outdoors.

Prevalence
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 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.

Genetics
Family history of atopy may be a factor in the development of more severe allergic reactions.

Risk Factors

• Previous sensitization
• Although most arthropod contact is inadvertent, some activities, occupations, and travel increase risk.
• Greater risk for adverse outcome in young, elderly, immunocompromised, and those with unstable cardiac or respiratory disease
• Increased risk of anaphylaxis in patients with mastocytosis (1)

General Prevention

• 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 (2)
    • Formulations with higher concentrations (20–50%) are first-line choice in areas of endemic arthropod-borne diseases (2).
    • Concentrations >30% have longer duration of action.
    • Safe for children >6 months of age and pregnant and lactating women (2)
  • Icaridin (formerly known as picaridin)
    • Concentrations <20% require more frequent applications to maintain activity.
  • P-menthane-3,8-diol (PMD-lemon eucalyptus extract)
    • Recommended alternative repellent to DEET at concentrations >20% (2)
    • May be used in children >6 months of age (2)
  • 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. Do not apply directly to skin. 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 (2).
• 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 decreased by prompt removal of ticks within 24 hours of attachment.