Pyemotes ventricosus Dermatitis: A Serpiginous Skin Lesion due to a Mite that Parasitizes a Wood-Boring Beetle

In July (midsummer) 2018, a 51-year-old man residing in a village in the Swiss canton of Valais developed two highly pruritic skin lesions. One large lesion was located on the abdomen and a smaller one on the left flank. Erythematous macules evolved from initial red spots to full size (pictured) within 24 hours. An erythematous serpiginous track extending cranially from the larger lesion developed in the subsequent 12 hours. Both lesions appeared shortly after he handled substantial amounts of logs and timber outdoors. Based on the lesions' central morphology, rapid evolution, and itchiness, the consulted family physician discarded the differential diagnoses of erysipelas with lymphangitis, erythema migrans due to Lyme disease, and cutaneous larva migrans and suspected an unusual arthropod bite or sting. He referred the patient to the medical department of the Swiss Tropical and Public Health institute for advice, where the spot diagnosis of Pyemotes ventricosus dermatitis was made. Under topical corticosteroid and oral antihistamine treatment, the lesions slowly regressed and finally disappeared.