Human dermatitis caused by the natural infestation of larval trombiculid mites Leptotrombidium akamushi (Brumpt, 1910) (Acari: Trombiculidae) at the hot spot of Tsutsugamushi disease in Akita Prefecture, Japan

Abstract

We observed the prognosis of clinical symptoms and histopathological alternations of human dermatitis in a 61-year-old man, who had been bitten by the unfed larval trombiculid mites Leptotrombidium akamushi (Brumpt, 1910), during a field survey of trombiculid mites at the hot spot of Tsutsugamushi disease on the river side of the Omonogawa River, Omagari, Akita prefecture. The victim first noticed bites by the L. akamushi larvae on 12 sites comprised thin or tender areas in the neck, elbow folds, armpits, and around the nipples approximately 12 hours’ post-infestation. The average mite-feeding period was 59.3 hours. The pain persisted for 24–96 hours after each larva detached. The small erythematous macules lasted for several days to 1 week and then subsided gradually, leaving residual pigmentation for approximately 1–2 weeks. Histopathological examinations of the victim’s skin at 30, 40, and 54 hours’ post-infestation revealed that the larvae had formed mesenchymal stylostomes that penetrated through the epidermis into the dermis. Inflammatory cells such as histiocytes, lymphocytes, and neutrophils were observed around the stylostomes, but few eosinophilic leukocytes were seen. This report differs from those of animal experiments because it clarifies the natural infestation time of L. akamushi larvae on the human body.