Comparative diagnostics reveals PCR assays on skin scrapings is the most reliable method to detect Sarcoptes scabiei infestations

Sarcoptic mange is a globally significant parasitic disease of humans and other animals, both domestic and wild. But clinical diagnosis of S. scabiei infestation, using the standard skin scraping followed by microscopy technique, remains highly variable (predominantly due to false-negatives), and a major challenge for human and animal welfare. Here, we utilised a unique sample set from bare-nosed wombats (Vombatus ursinus) to evaluate a variety of putatively useful diagnostic approaches for S. scabiei. Against the standard of skin scrapings followed by microscopy, we compared observational scoring of mange severity (often employed in field studies of wildlife), PCR on skin scrapings (recently proposed as an improvement for humans and other animals), and PCR on skin swabs (proposed a non-invasive method for humans and other animals). We find that observational scoring positively correlated with counts of S. scabiei from skin scrapings, particularly as mange severity increases, but underdiagnoses early mange. Species-specific PCR for S. scabiei on skin scrapings had enhanced capacity for mite detection relative to microscopy. Finally, the non-invasive sampling method of PCR on skin swab samples had a high congruence to skin scraping microscopy, however prospective false negatives as a consequence to sampling is concerning. To our knowledge, this is the first study to simultaneously assess this combination of methods for S. scabiei diagnosis. We conclude that PCR on skin scrapings as an advancement on traditional microscopy, and the other techniques (observational, skin swabs and microscopy) remain useful, but harbour greater false-negatives. Outcomes are transferrable to diagnosis of S. scabiei for other host species, including humans, particularly for crusted mange and potentially ordinary mange also.