Skin test and radioallergosorbent test characteristics of scabietic patients

The scabies mite Sarcoptes scabiei and the Dermatophagoides house dust mites (HDM) are related phylogenetically and are the sources of several cross-reactive antigens. The purpose of this study was to investigate the immune response to S. scabiei and HDM in scabietic patients. Skin test sensitivity and serum IgE to both S. scabiei and HDM were determined for patients who had or previously had confirmed ordinary scabies. A retrospective group included nine subjects who had received successful treatment three weeks to one year prior to the study. A prospective group included 16 subjects with active scabies. Allergic histories were obtained, serum was collected, and skin prick tests (SPTs) were performed at enrollment for all and periodically over the next 12 months for the prospective patients. None of the individuals in either group reported a known sensitivity to HDM. Six of the nine retrospective patients were SPT positive to both S. scabiei and HDM and two of these showed circulating IgE specific for these antigens. At diagnosis, 13 of 16 patients with active scabies were SPT positive to S. scabiei and 12 of these were also SPT and/or radioallergosorbent test positive to HDM. Six patients had circulating IgE directed at both S. scabiei and HDM antigens while one subject had IgE to S. scabiei only and another had IgE directed at HDM only. Twelve of the 15 subjects tested also showed IgE and/or IgG binding to one or more bands on Western blots of an S. scabiei-specific protein fraction. This study indicated that approximately half of the patients with active scabies had S. scabiei- and HDM-specific circulating IgE while most patients cured of scabies lacked S. scabiei- and HDM-specific serum IgE. The data also suggested that antibodies to S. scabiei in scabietic patients also recognize HDM; however, some antibodies were directed at scabies-specific antigens.