Lots of press coverage in the last couple of weeks about some startling discoveries borne out of mtDNA analysis of demodex mites in 80 subjects.
The discovery uncovered by this research is that the genetic type of mite variety seems to be exclusively passed from parent to child in much the same way as DNA is inherited by children from their parents.
Thus the genetic variability of the demodex mite population can serve as a proxy for the genetic history of their hosts.
Another startling reality is that demodex mites appear to have been part of human existence for as long as humans have existed – around 100,000 years.
Demodex Mites are OLD
So whilst D. folliculorum may be a recent arrival to the news cycle, it is not a newcommer to the human epidermis.
Whatever is the real issue with demodex and skin conditions like rosacea, it likely has been so for the lifetime of our species. Maybe we just need to tip the balance back towards equilibrium rather than total eradication.
We all have them. New study reveals that people from different regions host different mite lineages, supports “Out of Africa” theory.
SAN FRANCISCO (December 14, 2015) — Scientists have discovered a universal human truth about our bodies: they all, without exception, have mites.
A landmark new study, led by scientists at Bowdoin and the California Academy of Sciences, explores the fascinating, little-known natural history of the face mite species Demodex folliculorum, using genetic testing to link the microscopic animal’s evolution to our own ever-evolving human story.
By zooming in on a type of genetic material (called mitochondrial DNA) in mite samples from around the world, scientists discovered that different human populations have different mites, that those mites follow families through generations, and that they are not casually transferred between humans.
For most people, mites are harmless. For some, however, mites can be associated with various skin and eye disorders including rosacea and blepharitis. Trautwein says this is one reason among many that scientists need to learn more about these constant human companions.
“It’s shocking that we’re only just discovering how deeply our histories are shared with the mites on our bodies,” says Trautwein, who has traveled the world to sample mites and learn more about their cryptic lives. “They aren’t just bugs on our faces, they are storytellers. Mites tell us about our own ancient history—it’s a complex story, and we’ve only just scratched the surface.”
Human Origin Models
Some further analysis of the findings here, also worth some attention.
January 14, 2016, By Dr. Fazale Rana
Remarkably, scientists know very little about face mites despite their close relationship with humans. Scientists don’t have a full understanding of the role mites play in human health nor do they know how these creatures are transmitted from human to human.
To address this lack of understanding, an international team of scientists, headed up by an investigator from the California Academy of Sciences, recently characterized the genetic variability of D. folliculorum.
Not only did their work turn out to be a landmark study—it also carries implications for human origins models.
Studying Mite Genetic Variability
These researchers analyzed D. folliculorum mitochondrial DNA (mtDNA) sequences isolated from 70 people who had ancestries from different parts of the world (Africa, Europe, Asia, and Latin America). They discovered different versions (called haplotypes) of face mite mtDNA that corresponded to the geographic ancestry of the human test subjects. In other words, people with a family history from Africa, Europe, Asia, and Latin America harbored face mites with characteristically distinct mtDNA, respectively.
The investigators learned that parents and children had the same face mites; but seldom did they observe the same types of face mites for people from different family units.
From these observations, the scientists concluded that face mite infection requires close and sustained physical contact and, therefore, occurs most frequently from parent to child.
This pattern of transference closely mirrors the transmission of genetic material (which, of course, is from parent to child). Consequently, the genetic variability of face mites can serve as a proxy for the genetic variability of their human hosts.
In fact, the researchers point out that the pattern for the global genetic variability of face mite mtDNA is exactly what would be expected if the out-of-Africa model for humanity’s origin is valid.
Further Article Extracts
Proc Natl Acad Sci U S A. 2015 Dec 29;112(52):15958-63
Microscopic mites of the genus Demodex live within the hair follicles of mammals and are ubiquitous symbionts of humans, but little molecular work has been done to understand their genetic diversity or transmission.
Here we sampled mite DNA from 70 human hosts of diverse geographic ancestries and analyzed 241 sequences from the mitochondrial genome of the species Demodex folliculorum.
Phylogenetic analyses recovered multiple deep lineages including a globally distributed lineage common among hosts of European ancestry and three lineages that primarily include hosts of Asian, African, and Latin American ancestry.
To a great extent, the ancestral geography of hosts predicted the lineages of mites found on them; 27% of the total molecular variance segregated according to the regional ancestries of hosts.
We found that D. folliculorum populations are stable on an individual over the course of years and that some Asian and African American hosts maintain specific mite lineages over the course of years or generations outside their geographic region of birth or ancestry.
D. folliculorum haplotypes were much more likely to be shared within families and between spouses than between unrelated individuals, indicating that transmission requires close contact. Dating analyses indicated that D. folliculorum origins may predate modern humans. Overall, D. folliculorum evolution reflects ancient human population divergences, is consistent with an out-of-Africa dispersal hypothesis, and presents an excellent model system for further understanding the history of human movement.
and the full published article PDF