Ubiquity and diversity of human-associated Demodex mites

Abstract

Demodex mites are a group of hair follicle and sebaceous gland-dwelling species. The species of these mites found on humans are arguably the animals with which we have the most intimate interactions. Yet, their prevalence and diversity have been poorly explored. Here we use a new molecular method to assess the occurrence of Demodex mites on humans. In addition, we use the 18S rRNA gene (18S rDNA) to assess the genetic diversity and evolutionary history of Demodex lineages. Within our samples, 100% of people over 18 years of age appear to host at least one Demodex species, suggesting that Demodex mites may be universal associates of adult humans. A phylogenetic analysis of 18S rDNA reveals intraspecific structure within one of the two named human-associated Demodex species, D. brevis. The D. brevis clade is geographically structured, suggesting that new lineages are likely to be discovered as humans from additional geographic regions are sampled.

Figure 1. PCR based screen for presence of Demodex 16S rDNA in samples with no visually identifiable mites.

Lanes labeled 1–29 represent samples from single individual participants. Lanes labeled M represent 100 bp molecular weight size markers. (a) PCR products indicate the presence of Demodex DNA in 100% of the screened samples from individuals over the age of 18. (b) PCR products indicate the presence of Demodex DNA in 70% of the screened samples from individuals 18 years of age.

Figure 2. Maximum likelihood (ML) phylogeny of mites based on 18S rDNA sequences.

Support values (Bayesian posterior probabilities/ML bootstrap support) given next to major nodes in the topology. Scale bar indicates the number of substitutions per site. Icons indicate mite host.