The role of Demodex
Diane Thiboutot, M.D., professor of dermatology and vice-chair for Research at Penn State University, was on that AAD roundtable and says there are two things that have emerged in the literature when it comes to rosacea and Demodex.
“There’s a lot of evidence to demonstrate that patients with rosacea have more Demodex mites compared to patients without rosacea. But just the presence of Demodex, in and of itself, doesn’t induce rosacea. There seems to be a quantitative difference among Demodex mites in people with rosacea,” Dr. Thiboutot says.
Another important finding is the Demodex mites’ involvement with toll-like receptor-2 (TLR-2).
“There are studies to show that the Demodex mite is able to induce inflammation by activating the TLR-2,” Dt. Thiboutot says.
There’s a long way to go, however, before these findings translate to treatment. For example, TLR-2 activation is needed to fight off pathogens, so stopping it entirely isn’t an option.
“We need more studies looking at a cause and effect between the presence of Demodex and the development of rosacea, which can be challenging because, although rosacea is common, we really don’t have a clear idea of the exact steps involved in its pathogenesis,” Dr. Thiboutot says.
And while researchers are detecting the presence and quantity of Demodex by performing follicular biopsies, it might be too early for practicing dermatologists to think about testing for Demodex in their rosacea patients, according to Dr. Thiboutot.
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“I think that until there’s more information on Demodex, I don’t feel that follicular biopsies are necessary at the moment,” Dr. Thiboutot says.
Microorganisms and mast cells
Other microorganisms associated with rosacea include staph epidermidis, as well as a bacteria that lives on Demodex mites, called Bacillus oleronius.
“Bacillus oleronius may have a role in stimulating the immune system. All [the microorganisms] work by stimulating the TLR-2,” says Dr. Stein Gold, who was also a member of the AAD panel.
Another interesting direction into looking at what causes rosacea is in the study of mast cells.
“If you biopsy patients with rosacea, they seem to have more mast cells in their dermis,” Dr. Stein Gold says.
“There’s an interesting animal study that was done. If you take mice and inject the abnormal proinflammatory peptides that are found in rosacea, you can reproduce the signs and symptoms of rosacea. If you took those same mice and they don’t have any mast cells, that doesn’t happen. So, it does appear that mast cells have an important role, which might be an avenue of treatment down the line.”1