Conference Agenda

In recent years, the interest in molecular diagnostic methods for the detection of many pathogens has grown substantially. This escalation in interest has occurred in parallel with data indicating inaccuracy of scabies diagnosis based on currently available methods such as examination of skin samples by standard microscopy, burrow ink test and handheld dermatoscopy. Mites are very few in numbers at the early stage of the disease that makes it extremely difficult for even an experienced dermatologist to make a definitive diagnosis. Hence, scabies can be misdiagnosed as an allergic reaction or eczema. With the recent availability of the scabies genome, we developed a qPCR assay targeting a more abundant repetitive region to improve the sensitivity and specificity of a PCR-based diagnostic assay, alongside a non-invasive skin sample collection using FLOQ swabs. We have initially validated our qPCR methodology by testing samples from hospitalised cases in Darwin, NT and field collected samples from Kimberley, WA and Auckland, NZ. Recently, we have optimised our assay using the digital PCR format and have demonstrated a much higher sensitivity and specificity in detecting scabies, representing a major advance. Results of our studies showing its utility in improving clinical diagnosis of scabies will be presented.

Scabies is one of the most common skin diseases worldwide and is caused by the parasitic mite Sarcoptes scabiei. Unbearable itch is the cardinal symptom of scabies. Scratching in response to itching facilities the entrance of pathogenic bacteria into the skin and can lead to life-threatening sequelae. The mechanisms underlying the scabies itch are poorly understood, hence scabies itch targeted therapies are missing. Due to the non-responsiveness to anti-histamines, a histamine-independent pathway is proposed for scabies itch. We aimed to investigate the expression of non-histaminergic itch markers(MRGPRX2, tryptase, periostin, NK1R, epidermal nerve fiber density (ENFD) and substance P) ex-vivo over a course of scabies infection in a scabies pig model. Skin biopsies from three scabies infected pigs were collected pre-infection and 2, 4, 8, 12 and 20 weeks post-infection. Primary antibodies for above listed markers and cy-3 labelled secondary antibodies were used immunohistologically. Aperio FL slide scanner and QuPath software were used to image and quantify itch markers. We observed significant increase in typtase⁺ mast cells, MRGPRX2 positive cells, periostin, and NK1R expression, and reduced ENFD at 2 Weeks post-infection, coinciding with clinical onset of the scabies-associated itch in this model. We propose that scabies infection induces the non-histaminergic pathway.

The last formal study of scabies in New Zealand was conducted in 1978, indicating little interest has been given to this mite for more than forty years. Studies conducted in Pacific Island nations and in Aboriginal and Torres Strait Islander populations show a high prevalence of scabies, with common complications such as impetigo and bacterial skin infection. Our recent surveys of scabies in Auckland have shown an alarmingly high prevalence (36.5%) in predominantly preschool children living in sociodemographically deprived areas. Many children who were identified with scabies during the survey were treated for other diagnoses with topical steroid cream and other anti-pruritic lotions. Other work we have conducted shows a very strong statistical association between scabies and acute rheumatic fever: an important cause of ethnic inequality in health status in New Zealand children. Our work highlights the importance of improving the clinical diagnosis of scabies using molecular techniques such as the polymerase chain reaction test, and further understanding the prevalence of and improving treatment for this neglected tropical disease.