Abstract/Summary

Demodex mites (Acari) are highly specialised arthropods which infest the hair follicles of most mammals, including humans. Two species have been detected in human skin, Demodex folliculorum Simon, 1842 and D. brevis Akbulatova, 1963. They are common, intracutaneous parasites of the pilosebaceous complex and meibomian glands and can be found on the face, forehead, chest, neck, eyelids, eyebrows, scalp and the ear canal. The pathogenesis of human Demodex mites is far from well understood, but skin diseases such as gland dysfunction, dermatitis, rosacea and even follicular basal cell carcinoma may be caused by them. This study contributes to our knowledge of human Demodex biology with an evaluation of, and improvements on, existing methods for their microscopic identification. No method is currently available to sustainably rear these mites in vitro, so research continues to rely on de novo collection from willing hosts, a laborious and unreliable process. We investigate some published rearing media and propose new formulations for artificial media that may lead to success in this important area. We analysed the prevalence of Demodex mites in samples from human subjects of different ages, ethnicities, host’s sex, birth modes and postnatal feeding regimes, and found that age and postnatal feeding were influential on rates of infestation. Protocols and primer combinations are developed for a new, single, multiplex PCR reaction for DNA-based identification of mite species hosted by humans, which also includes the commonly carried dog mite, D. canis. The multiplex PCR successfully discriminated the three species, based on DNA fragment sizes and was also tested successfully on mites from several host ethnic groups. Finally, we assessed various proprietary kits and protocols for extracting, purifying and quantifying genomic DNA from D. brevis, since full nuclear sequences is not yet available for this species. The quality of resultant genomic DNA samples and the limitations of the kits are discussed. We make recommendations for further research and methodological improvements that may take forward our important contributions to the biology and DNA based identification and characterisation of these mites.