A Histopathologic Study of the Human Skin in the Early Stage After a Tick Bite: A Special Reference to Cutaneous Tissue Reaction to the Cement Substance of Tick Saliva

The Ixodidae family of hard ticks has cement-producing and non-cement-producing species. Involved skins of four patients bitten by cement-producing ticks and two by non-cement-producing ticks were histopathologically examined. Those of the latter two patients were also studied immunohistochemically to characterize the infiltrating inflammatory cells. In patients with cement-producing ticks, the cement substance was observed as external cement or outer zone of internal cement, respectively. Coagulative necrosis was present in the epidermis in one patient and from the epidermis to the dermis in another patient. Epidermal cells were damaged in the remaining two patients. Despite these severe tissue damages, the cutaneous inflammatory reaction in all four patients was very mild. In contrast, the patients bitten by non-cement-producing ticks had severe cutaneous inflammatory reaction. In addition to caseous necrosis-like change in the entrance site of the inserted mouthparts, extensive interstitial lymphohistiocytic infiltrate was present diffusely from the dermis to the subcutaneous tissue. In one of the patients coagulative necrosis was present from the dermis to the subcutaneous tissue. Immunohistochemically, the infiltrating lymphocytes were T-cell dominant and mixed moderately with B-cells. Pathogenetically, the cutaneous inflammatory reaction is only mild in the skins involved by the cement-producing ticks, perhaps because inflammatory reaction in the host skin is suppressed by antiinflammatory and immunosuppressive substances contained in tick’s saliva in order to prevent position of their mouthparts fixed to the host skin from rejection of the host until finishing their engorgement. In contrast, the cutaneous inflammatory reaction induced by the non-cement-producing ticks is severe, possibly because these ticks have no antiinflammatory and immunosuppressive substances in their saliva, and because their saliva is much more injurious than that of the cement-producing ticks.