trombiculidiasis

Trombiculidiasis is an infestation of humans or animals by the larval stage of mites in the family Trombiculidae, commonly known as chiggers. In humans, the larvae attach to the skin and feed for a few days before dropping off. Adults are free-living and do not parasitize hosts.

Etiology and life cycle: Trombiculid mites have a three-stage life cycle: egg, larva (the parasitic stage), nymph, and adult. Only the larvae are obligate ectoparasites of vertebrates, including humans; they attach to the skin, secrete saliva that digests tissue, and feed on the resulting fluid, typically for a few days before detaching. Some regional species can serve as vectors for Orientia tsutsugamushi, the agent of scrub typhus, but trombiculidiasis refers to the localized skin reaction rather than a systemic infection.

Clinical features: After exposure, individuals typically develop intense itching and a localized rash within hours to days. The bites appear as small red papules or vesicles, frequently around the ankles, waist, groin, or areas where clothing is tight. Pruritus can be severe, and scratching may lead to secondary infection.

Diagnosis and differential: Diagnosis is usually clinical, based on exposure history and the characteristic itching and lesions. There are no specific laboratory tests for trombiculidiasis. The condition can be confused with other causes of dermatitis, including mosquito bites, contact dermatitis, or scabies.

Management: Treatment is supportive. Topical corticosteroids and oral antihistamines can relieve itching; keeping nails short and using antiseptics can prevent secondary infection. Cleaning the skin and avoiding infested areas is advised. Prevention focuses on protective clothing, repellents such as DEET, permethrin-treated clothing, and good hygiene after outdoor exposure.

Prognosis and epidemiology: Trombiculidiasis is typically self-limited, with symptoms resolving within days to weeks after exposure. It is more common in warm, humid climates and rural or forested areas where people encounter vegetation.