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Trombiculosis
4 Interesting facts of Trombiculosis
- Chigger bites are caused by the larval stage of certain species of trombiculid mites.
- No treatment is reasonable because the lesions are self-limited. Topical products with pramoxine may provide some limited but immediate relief from the pruritus.
- The lesions resolve over 5 to 14 days.
- The prevention of chigger bites is helpful, typically by applying N,N-diethyl-3methyulbenzamide (DEET) to the skin, using DEET-impregnated clothing, wearing long pants, and tucking pant legs into boots when hiking.
Etiology and Risk Factors
Chigger bites are caused by the larval stage of certain species of trombiculid mites. In the United States, the predominant species is Trombicula alfreddugesi, and chiggers occur chiefly in the humid portions of the Midwest and Southeast. The red six-legged larvae lie in ambush on blades of grass or other short vegetation (typically, <15 inches off the ground), leap onto a passing host, and attach and feed for 3 to 4 days before dropping to the ground. The chigger is smaller than 1 mm in size and can barely be seen by the human eye.
Workup
History
- A clinical history of discrete erythematous papules, in appropriate areas, and after outdoor activities in an endemic area, should strongly suggest the diagnosis.
- Chiggers are found chiefly in the southeastern and south central United States and are not present in the Rocky Mountains.
Physical Examination
- The primary lesion is a red papule that may demonstrate a small, central, punctum-like area.
- Marked pruritus is a near-constant feature.
- Lesions occur in crops and are notoriously grouped on the ankles, behind the knees, or along points of pressure or contact of clothing.
- Patients with considerable sensitivity to chigger bites may develop bullous lesions, but this is uncommon.
- Secondary excoriation may be more impressive than the primary lesion and may lead to persistent papules or superimposed prurigo nodules.
- Secondary bacterial infection may also occur.
Diagnostic Procedures
- Skin scrapings may demonstrate the mite on rare occasion, but because the organism is only present transiently and does not complete its life cycle on humans, this is not typically used.
Treatment
Approach to Treatment
- No treatment is reasonable because the lesions are self-limited.
Patient Myth
Many patients have been taught by their families and friends to treat chigger bites with nail polish or various glues to suffocate the mite. In many cases, the mite has already dropped off. Occlusion actually increases heat retention at the site of the bite, which will increase pruritus. The only potential benefit is that the polish or glue will reduce skin damage from excoriations.
Drug Therapy
- Topical products with pramoxine may provide some limited but immediate relief from the pruritus.
- Potent topical corticosteroids applied bid provide modest relief in 24 to 48 hours.
- For exceptional cases only, intralesional triamcinolone (2.5 mg/mL) may be used to reduce inflammation and decrease pruritus.
References
1.Hohenberger ME, et al. What’s eating you? chiggers. Cutis. 2017;99(6):386-388.
