The effect of immunosuppression with cyclosporin A on the development of sheep scab.

The present study confirms that following infection with the ectoparasitic sheep scab mite, Psoroptes ovis, there is a rapid (within 24 h) inflammatory influx of eosinophils and apoptosis of the keratinocytes at the site of infection. In order to investigate whether these inflammatory reactions are important in the maintenance of mite infection, a group of animals were treated daily after the establishment of infection with the potent anti-inflammatory drug, Cyclosporin A. The course of infection was monitored by determining the lesion area and mite numbers, systemic antibody and blood eosinophils, as well as the inflammatory cells and T cell sub-populations within the lesion throughout the 6-week duration of the experiment. These parameters were compared with those in a similar infected control (non-treated) group. In control infected animals, the lesion area and mite numbers increased steadily throughout the 6-week period. In contrast, lesion area and mite numbers were severely depressed in the group which received Cyclosporin A. Local and systemic eosinophils, and systemic antibody were also significantly reduced in the drug treated animals, compared to controls. Surprisingly however, the number of lesional pan T cells, T helper cells, gammadeltaT cells and dendritic cells in Cyclosporin A treated animals were either the same, or significantly (P < 0.05) enhanced when compared to the control infected animals at the termination of the experiment. The results will be discussed in terms of the role of the dermal inflammatory response in the establishment and maintenance of the sheep scab mite.