2.4.7 Arthropod reactions

Synonyms

Ticks, stings, arthropod reaction

Epidemiology

Prevalence: hard to estimate because of different types of arthropods and environmental considerations. Most cases do not require medical intervention; more often in tropical climates.

Definition

It is necessary to distinguish between:

  1. Reactions to toxins from insect, spider, mites and tick bites
  2. Reactions to bites of parasitic insects, spider, mites and ticks
  • Permanent ectoparasites: parasitic insects (or arachnids = mites, ticks) live and/or feed on humans, are highly adapted and may be found on human hosts.
  • Temporary-accidental ectoparasites: bite humans by chance, the bite reaction varies greatly, and the parasite is rarely found on patients.

Aetiology & Pathogenesis

Human ectoparasites.


Permanent ectoparasites insects: head louse, clothing louse, pubic louse. Arachnids: Demodex and Sarcoptes scabei. Spiders of different types.
Accidental parasitic insects: bed bugs, fleas, mosquitoes, sandflies, gnats, flies and horse flies.


Accidental parasitic arachnids: ticks, Neotrombicula (see Trombiculosis), bites mites (Dermanyssus), non-burrowing animal mites (Cheyletiellidae = walking mange), animal forms of scabies (Sarcoptidae and others).

 

Sometimes symptoms may be due to neurotoxins.

Signs & Symptoms

Immediate and delayed reactions at site of sting: erythema, macules, papules, wheals and blisters.


The nature of the reaction depends more on the sensitivity of the victim, rather than the nature of the stinging insect.

Localisation

Exposed skin areas: head, neck, extremities.

Classification

See Aetiology and Pathogenesis.

Laboratory & other workups

None specific.

Dermatopathology

Not necessary.

Course

Varies from self-limited mild local reaction to life threatening anaphylactic reactions.

Complications

Persistent arthropod reaction with other complications: pseudolymphomatous reactions, persistent prurigo nodularis-like lesions, secondary bacterial infection. Arthropod borne systemic infections.

Diagnosis

Clinical features (grouped or linearly arranged pruritic papules, sometimes with central haemorrhagic punctae (purpura pulicans).

Differential diagnosis

For insect bites reactions: folliculitis, impetigo, furuncle, carbuncle, prurigo, dermatitis herpetiformis, erysipelas, blistering diseases.

Prevention & Therapy

Insect bite reaction from parasitic insects: topical antipruritic agents (zinc oxide lotion, anti-pruritic cream, corticosteroid lotions). Antihistamines in special situations of IgE mediated reactions (e.g. mosquitoes).


Prevention: protective clothing, sleep under fine-mesh nets, repellents.

Special

None. 

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