Hypersensitivity to house dust mites in patients with scabies

Background: Since they are related phylogenetically, house dust mites (HDM: Dermatophagoides pteronyssinus=Dp, and dermatophagoides farinae=Df) and scabies mite (sarcoptes scabiei=ss) show great physical and antigenic similarities. Therefore, circulating antibodies against scabies mite antigens may have been cross reactive to HDM antigens. Objective: Our aim was to detect HDM hypersensitivity by skin prick test (SPT) in patients with scabies. Methods: Fifty non-atopic scabies patients, and 50 non-atopic healthy people enrolled in the study. History of scabies in the past was regarded as an exclusion criteria. SPT with standardized HDM "mixed" extract was performed in all patients and controls. Results were evaluated as positive, if HDM extract-induced wheal was at least three mm larger in diameter than the negative control. All patients were treated with anti-scabies agents after SPT evaluation. Control examinaion was planned at the end of the third month. Results: While only six out of 50 healthy controls (12 %) had SPTpositivity against HDM, it was found to be positive in 16 out of 50 scabies patients (32 %) There was a statistically significant difference between two groups for skin test positivity (p<0.05). We were able to follow only six out of 16 SPT (+) patients. Besides having mild pruritus, they were still SPT-reactive at the end of the third month. Conclusion: The results obtained from this study lend support to the view that patients with scabies develop reactivity against HDM. As a result, it may be suggested that: The cross- reactivity between ss and HDM may partly explain the persistence of pruritus in some properly treated scabies patients: Since the period during scabies infestation and post-treatment phase might be regarded as "SPT- reactive state against HDM" at least in some cases, one more should be added to the questions asked during the evaluation of a patient for SPT: "Have you ever been treated scabies in recent months?".