Demodex folliculorum is a microscopic mite that lives on our skin . New research led by Bangor University and the University of Reading (UK) in collaboration with the University of Valencia, the University of Vienna and the National University of San Juan (Argentina) concludes that this “bug” is becoming a such a simple organism due to its peculiar way of living that it could soon be one with us, going from being an external parasite to being an internal symbiont .
Mites are transmitted at birth and almost all humans have them, reaching their maximum number when we are adults. They are about 0.3 mm long and live in hair follicles on the face and nipples , including eyelashes. Its food is the sebum released by the cells of the pores. They are activated at night and move between the follicles in search of a mate. And yes, when they find her they mate with her. On your skin. They also defecate. On your skin.
In the study that concerns us, the researchers have sequenced the genome of the D. folliculorum mite for the first time and have discovered that it has an isolated and inbred existence. These circumstances are promoting the transition from external parasite to internal symbiont, that is, it merges with us.
“We found that these mites have a different arrangement of body part genes than other similar species, because they have adapted to a protected life inside the pores. These changes in their DNA have given rise to some characteristics unusual body shapes and behaviors,” said Alejandra Perotti, associate professor of invertebrate biology at the University of Reading, who co-led the research.
What the DNA study of Demodex folliculorum has revealed
To begin with, these mites lead an isolated life in the pores of our skin . They have no outside threats, they have no competition to infest hosts, and they do not encounter other mites that have different genes. Its genetic reduction has turned D. folliculorum into an extremely simple organism that moves its dwarf legs using only three unicellular muscles. In addition, they survive with a minimal amount of protein, the lowest seen in this and related species.
Genetic reduction also influences the nocturnal behavior of D. folliculorum . It has neither UV protection nor the gene that makes animals wake up in daylight. They are not capable of producing melatonin, but they can use the one that we secrete at night to fuel their nocturnal mating sessions.
Continuing with the matter of mating, these mites never cease to amaze, as the males have their penis in the front part of their body and it protrudes upwards. When copulating, they must therefore be placed under the female while both hold on to our hair.
Another interesting feature that the research team has discovered is that the mites have many more cells at a young age compared to their adulthood. This is something that goes against what was previously thought, that is, that parasites reduce their number of cells at the beginning of development. This characteristic leads the researchers to think that it could be the previous step for the mites to become symbionts.
Finally, there are those who have maintained throughout this time that mites do not have an anus and consequently must accumulate feces during their lives before releasing them when they die, causing inflammation in our skin. The new study confirms that they do have anus , which could have unfairly blamed them for certain skin conditions. “Mites have been blamed for many things. The long association with humans might suggest that they might also have simple but important beneficial functions , for example, keeping the pores on our face unclogged,” said Dr. Henk Braig, co-author of Bangor University and Saint John’s National University.
Referencia: Perotti, A., Braig, H. et al. 2022. Human follicular mites: Ectoparasites becoming symbionts. Molecular Biology and Evolution.
