THE DEVELOPMENT OF PROTECTIVE IMMUNITY IN CANINE SCABIES

Seven of eight dogs that had been previously infested with Sarcoptes s cabiei var. canis and then cured, expressed protective immunity when e xperimentally reinfested with scabies. All seven dogs that expressed r esistance were spontaneously cleared of scabies by 64 days after they were experimentally reinfested. Five of the eight dogs were free of sc abies by 24 days. The sequential changes in the inflammatory/immune ce llular infiltrate in the scabietic lesions of each dog were determined during the sensitizing infestation, cure and the subsequent experimen tal reinfestation (challenge). During the initial infestation and in t he subsequent challenge reinfestation, dogs developed mixed cellular i nfiltrates in their scabietic lesions that contained mononuclear cells , neutrophils, plasma cells and mast cells. Reinfestation induced more rapid increases in the densities of these cells than had occurred dur ing the sensitizing infestation. Mononuclear and mast cells were the m ost numerous infiltrating cells during the sensitizing phase. During t he challenge phase the most numerous infiltrating cells were mononucle ar cells and neutrophils. The sensitizing and challenge infestations i nduced circulating scabies-specific antibody responses, but the respon se was more rapid during the reinfestation challenge. Both the cell-me diated response in the skin and the circulating antibody response wane d in parallel with clearing of the mites following reinfestation.