Abstract
The progression of human cutaneous reactions, caused by the bite of non-infected unfed larval trombiculid mites, Leptotrombidium pallidum and/or L. scutellare was observed by applying unfed larvae to the flexure of the wrist of the forearm of two human volunteers. The histopathology of human skin in response to stylostome formation was also examined. Unfed larvae were also applied to laboratory mice. The infestation rate of L. scutellare (60.0-93.3%) was higher than that of L. pallidum (5.0-40.0%) on human skin. However, the infestation rates of L. pallidum and L. scutellare on mice were similar (63.5% and 57.0%, respectively) and showed no significant difference (P>0.05). The feeding period of L. pallidum (52.5-76.0 hrs) was longer than that of L. scutellare (42.3-51.4 hrs) in both human volunteers. However, the average feeding period of L.scutellare (45.1 hrs) on human skin was shorter than that on mice (60.2 hrs). The skin reactions to the L. scutellare and L. pallidum infestations differed in the two human volunteers. Volunteer A developed a slight skin reaction, whereas volunteer B exhibited a severe skin reaction. Specifically, a vesicle and bulla formations accompanied by pain and pruritus were observed at the bite site of volunteer B in every experimental infestation. The stylostomes formed by L. pallidum and L. scutellare were epidermal stylostomes, which did not extend beyond the basal layer of epidermis. All stylostomes exhibited considerable inflammation in the epidermis and similar reactivity.
