Sequential histopathology at the Rhipicephalus sanguineus tick feeding site on dogs and guinea pigs

The tick Rhipicephalus sanguineus is a very common parasite of dogs worldwi de. Dogs seem unable to acquire resistance against this tick species, where as guinea pigs demonstrate a very strong resistance following primary infes tation. We studied the inflammatory reaction at the R. sanguineus tick feed ing site on dogs and guinea pigs during primary and tertiary infestations a t different time intervals after attachment. Biopsies were collected after 4, 24, 48 and 96 hours. Changes that were found in all experimental groups included a cone of cement around the mouthparts of the tick, epidermal hype rplasia, edema and inflammatory cell infiltration in the dermis directly un derneath the tick attachment site. Dogs reacted to ticks mainly with neutro phils, particularly after repeated exposure. Mast cells and mononuclear leu kocytes were also present. Guinea pigs reacted to R. sanguineus mainly with mononuclear cells, eosinophils and basophils. These cells were particularl y numerous after repeated exposure to R. sanguineus. Our results suggest th at basophils and eosinophils are involved in resistance of guinea pigs to R . sanguineus and that neutrophils in dogs have little effect against this t ick species.