Morphological characterization of stylostome and skin reaction produced by Leptotrombidium album (Acariformes, Trombiculidae) on the bat Barbastella pacifica from Kunashir Island

Abstract

Larvae of the chigger mite Leptotrombidium album (Kamo, Kawashima & Nishimura, 1957) (Acariformes, Trombiculidae) are found in Kunashir island and recognized as parasites of bats Barbastella pacifica (Kruskop, Kawai & Tiunov, 2019) for the first time. Larvae were measured and photographed using SEM and DIC approaches. A stylostome is described in bats for the first time by histological with additional CLSM, DIC and polarized light methods. The stylostome belongs to the mesenchymal type and penetrates deep into the host dermis perpendicular to the skin surface. The stylostome is a straight relatively wide (80 µm) tube and may reach 250 µm long in the maximum development. The axial stylostome canal varies from 7.5 to 20 µm wide and distally is opened to the subjacent host tissue. A particular eosinophil cone of a gel consistency to which the larval cheliceral blades are tightly cemented represents the proximal stylostome portion. The main stylostome portion usually remains unstained and also shows a gel-like consistency. The distal stylostome portion—supposedly a fresh saliva portion—is typically stained by Azur in blue and seems to be a transitional condition between sol to gel. No birefringent components are found in the stylostome substance. The stylostome may immediately contact host tissues or may be surrounded by a mixed eosinophil substance composed of destroyed inflammatory cells. If present, this substance is tightly associated with the stylostome walls and may be considered as an analog of scab but distributed not on the surface but inside the skin. The stylostome formation is accompanied by a generalized inflammatory reaction with the predominance of neutrophil leukocytes. The activity of basophils, lymphocytes, macrophages and mast cells is relatively weak. A particular tissue sinus filled with inflammatory cells, an analog of the feeding cavity, situates underneath the stylostome. The disclosed stylostome organization confirms its species-specific character.