2.4.3 Trombidiosis

Grading & Level of Importance: B

Review:

2026

W. Burgdorf, Munich; J. McGrath, London;
Revised by Z. Bukvić Mokos, Zagreb; B. Marinović, Zagreb

Overview:

ICD-11
Synonyms
Epidemiology
Definition
Aetiology & Pathogenesis
Signs & Symptoms
Localisation
Classification
Laboratory & other workups
Dermatopathology
Course
Complications
Diagnosis
Differential Diagnosis
Prevention & Therapy
Special

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.

The skin reaction is caused by the larval form of Trombicula, a small plant mite (about 0.3 mm). It is sometimes known as harvest mites because they often infect grains, but they are also acquired in gardens and forests. Mites attach to passers-by and using enzymes to create a hole in the epidermis through which they can receive nutrients. The chemicals they release during this process cause intensive pruritus.

Signs & Symptoms

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

Usually, it starts with a small macule or wheal, which after 1-2 days develop to pruritic papules and /or papulo-vesicles. The lesions can last several weeks, during which they become excoriated. Secondary infection is possible.

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.

In general, a symptomatic therapy with topical corticosteroids or antipruritic agents is the first line. Systemic antihistamines can be given. Regular use of repellents is effective. They should be applied about the clothing lines. Prophylaxis: avoidance of risk areas (gardens, parks, compost piles), insect repellents for garden work.