2.4.3 Trombidiosis

Grading & Level of Importance: B

ICD-11

NE61

Synonyms

Harvest itch, chigger itch

Epidemiology

Larvae are most prevalent in forests and long and overgrown grass in fields and gardens in late summer and fall. In tropical areas, the infection may occur at any time of the year. The natural hosts are small rodents.

Definition

Pruritic skin lesions caused by mite larvae (chiggers) of the Trombiculidae family.

Aetiology & Pathogenesis

Larval mites (Trombicula autumnalis): 0.3 mm, transfer from vegetation to skin, usually late summer, bite human as accidental host, inject proteolytic agent  then suck up debris and drop off.

Signs & Symptoms

Intensely pruritic papules and macules with haemorrhagic central punctae (site of bite), sometimes vesicles.

 

Localisation

Sites where clothing is tight (belt line, tight cuffs), proximal thighs, popliteal fossae, ankles. Often several lesions in a linear pattern.

Classification

None. 

Laboratory & other workups

Not required.

Dermatopathology

Lymphomononuclear cell infiltrate with eosinophiles in the dermis. Focal parakeratosis and spongiosis in the epidermis, sometimes vesicles around sting.

Course

Usually resolves spontaneously. 

Complications

Bacterial superinfection; “summer penile syndrome”.

Diagnosis

Clinical features and history (exposure in known endemic areas). Almost impossible to find larva on human. Sometimes larva found outdoors.

Differential diagnosis

Prurigo, other arthropod bites.

Prevention & Therapy

Topical antipruritic agents (zinc or corticosteroid lotion). Systemic antihistamines. Prophylaxis: avoidance of risk areas (gardens, parks, compost piles), insect repellents for garden work.

Special

None.

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