Skin mites in humans - from parasites to symbionts
They live in human hair follicles on the face, eyelashes and nipples - microscopic mites whose genetics have been extensively examined in a recent study for the first time. It turned out that the most common species of skin follicle mite is completely dependent on humans and can no longer exist outside of them.
An international working group has analyzed the DNA of the Demodex folliculorum mite for the first time. The findings, recently presented in the journal Molecular Biology and Evolution, show that mites living in skin pores have lost many genes and cells as a result of inbreeding and isolation and are approaching permanent existence with humans.
Almost everyone harbors dust mites
Demodex folliculorum mites about 0.3 mm long live in the pores of almost everyone's skin. Nocturnal animals feed on the sebum that is released from the cells in the pores.
Man as a nest for mites
However, they cannot survive outside the pores, as the research team has just discovered. "Because of this close and permanent link with humans, the mite grew enormously and lost many genes," confirms study co-author Alejandro Manzano Marín from the University of Vienna.
"They survive with a minimal repertoire of proteins - the lowest number ever observed in this and related species," explains the scientist.
According to him, it is surprising that mites have many more cells when they are young than when they are adults. This contradicts the previous hypothesis that parasitic animals reduce their cell number early in development.
Use for humans unclear
"We conclude that the mites develop from an external parasite into a permanent symbiont of humans", explains Manzano Marín. So far, however, it is unclear whether this symbiosis is also beneficial for humans.
The complete breakdown of genetic information provided detailed insights into the tiny organisms' unusual physical characteristics and lifestyle. Among other things, the mites have lost all genes for protection against UV rays, which explains the nocturnal activity of small animals.
Dust mites do not cause skin diseases
“Some researchers had previously assumed that the mites had no anus and therefore had to collect all their excrement during their lifetime before releasing them when they died and thus causing skin inflammation,” reports Manzano Marín.
However, according to the expert, the results of the study confirm that the mites do have an anus and are therefore "wrongly responsible for many skin diseases", points out Manzano Marín.
An evolutionary impasse
Mites live in the pores of the skin without enemies, competitive pressure or outside threats. The mites are often transmitted to the baby via the mother's breast. However, the lack of contact with partners with other genes could become an evolutionary dead end for mites.
“Inbreeding leads to an accumulation of harmful mutations, and bad genetic variants end up spreading quickly,” Manzano Marín points out. This could eventually lead to the extinction of this species of mite in the long term. (vb)
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This text corresponds to the requirements of the specialized medical literature, medical guidelines and current studies and has been verified by health professionals.
Graduate editor (FH) Volker Blasek
Sources:Gilbert Smith, Alejandro Manzano Marín, Henk R Braig, et al. : Human follicular mites: ectoparasites become symbionts; in: Molecular Biology and Evolution (2022), Academic.oup.comUniversity of Vienna: Symbiote instead of parasite: mites in our skin pores become part of us (published: 22/06/2022), medienportal.univie .ac.at
This article contains general advice only and should not be used for self-diagnosis or treatment. It cannot substitute a visit to the doctor.