Reliable Diagnostic Test Developed for Scabies

Scabies antigen specific immunoglobulin E (IgE) was measured by a dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA) and quantified, while a competitive inhibition enzyme-linked immunosorbent assay (ELISA) was also conducted.

Scientists from the Menzies School of Health Research, (Darwin, NT, Australia) collaborated with other institutions, to create recombinant allergens to S. scabiei and house dust mites (HDM). Specific IgE antibodies to a major scabies antigen recombinant Sar s 14.3 (rSar s 14.3) were measured in 140 plasma samples from scabies-infested and control subject groups. The 140 consenting volunteers consisted of six groups: 30 subjects with crusted scabies; 30 subjects with ordinary scabies; 30 previously exposed but currently noninfested subjects; 30 subjects naïve to scabies; 10 naïve subjects with atopic allergy as defined by positive skin prick test to a panel of common aeroallergens; and 10 naïve subjects with known allergy to human dust mites based on clinical history and positive specific IgE.

The mean IgE binding to the recombinant antigen for the crusted scabies group was significantly greater compared to each of the other groups. The ordinary scabies group also had a significantly higher mean value than each noninfested group, and the exposed but noninfested group's mean IgE response was significantly greater than the mean response for the naïve to scabies group. The recombinant antigen DELFIA (Wallac; Turku, Finland) showed excellent diagnostic capability, with 100% sensitivity and 93.75% specificity for distinguishing subjects with current scabies infestation from control, uninfested subjects.

The authors concluded that the results demonstrate sensitive detection of IgE reactivity with genus-specific scabies mite epitopes and differential diagnosis of scabies mite allergy from allergy to HDM. The recombinant antigen specific IgE DELFIA has high diagnostic efficiency, with accuracy superior to other diagnostic methods currently available for scabies. Due to the high sensitivity, specificity, accuracy, predictive values, and area under the ROC curve, the developed DELFIA represents a marked improvement for the clinical diagnosis of scabies and helps direct future development of a specific diagnostic tool for scabies. The study was published on October 21, 2011, in the journal Diagnostic Microbiology and Infectious Disease.

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Menzies School of Health Research
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