Investigative studies of the dermatitis caused by the larva of the brown-tail moth (Euproctis chrysorrhoea Linn.) II. Histopathology of skin lesions and scanning electron microscopy of their causative setae.

Two different aspects related to the dermatitis caused by the so-called nettling hairs of the larva of the brown-tail moth, Euproctis chrysorrhoea L., are documented. The first part describes the sequence of histopathologic changes associated with the inflammatory process in the human skin induced by epicutaneous application untreated (UT-N) and heat treated (HT-N) nettling hairs. The penetration of untreated and heat treated nettling hairs into the epidermis is evident from their presence in 12 out of 29 UT-N lesions and 5 out of 10 HT-N lesions respectively. The introduction of nettling hairs into the skin leads to damage and bulla formation of the surface epithelium and early inflammatory signs consisting of edematous changes of the dermis and pervascular infiltration of neutrophils, eosinophils and mononuclear leucocytes. After few hours the intensity of the dermal infiltrate has increased and spongiotic changes appear. After 48--72 h the perivascular infiltrate is mainly composed of mononuclear cells, while along with increased spongiosis the damaged surface epithelium may show repair. The traumatic changes of the surface epithelium in HT-N lesions appear less prominent in comparison with the UT-N lesions. The second part describes the findings obtained by scanning electron microscopy of the nettling hairs. Evidence is brought forward to support the view that the offending setae may be looked upon as tapering, hollow microcapillaries which are open at both ends. The present findings are consistent with the idea that the nettling hairs may serve as microneedles from which irritant substances may be liberated when penetrating into the skin, and that the resulting inflammatory reactions are attributable to combined mechanical and toxic effects.