Skin reactions induced by experimental exposure to setae from larvae of the northern pine processionary moth (Thaumetopoea pinivora)

Background: Moth larvae that carry noxious hairs (setae) are spread worldwide. A population of the northern pine processionary moth (Thaumetopoea pinivora, TP) is present on the island of Gotland in the Baltic Sea. This study aimed to evaluate the local skin reactions following experimental exposure to TP setae. Subjects and Methods: A drop of setae suspension was applied on the volar forearm of six volunteers. The local skin reactions were studied by microscopy and skin perfusion using laser Doppler (LD) scanning. Results: Setae penetrated into the skin, and LD scanning showed marked increase in blood perfusion in all subjects. In two, with a history of severe symptoms, microscopic vacuoles developed around setae, followed by desquamation and severe symptoms. Remaining individuals, with only light symptoms during previous exposure, exhibited only mild reactions that disappeared within 3 weeks. In none of the volunteers, immunoglobulin (Ig) E or IgG4 antibodies to larval antigens were found. Conclusion: Experimental skin exposure to TP setae induces local inflammatory reactions independent of earlier exposure to TP. The degree of reaction correlated well with the magnitude of symptoms during natural exposure. The initial reaction mimics a ‘foreign body reaction’ that varies depending on individual predisposition.