Demodex mites with associated T-cell exhaustion could be central to the cause of rosacea with papulopustules (PPR), according to findings from a review published in the Journal of the European Academy of Dermatology and Venereology. Demodex proliferation seems integral to a multifactored causal network directing the occurrence and severity of inflammatory symptoms.

Recent increasing evidence suggests that Demodex mites play a key role in the rosacea inflammatory process; Demodex mites are also the cause of demodicosis. The reviewer aimed to analyze the role of Demodex in the cause and development of rosacea to determine if the cause of PPR could be credited to Demodex proliferation.

According to data in the review, more than 98% of patients with PPR present much higher Demodex densities than patients with healthy skin. The deeper in the skin the Demodex mites, the less likely they are to be detected, but they ignite deeper inflammation resulting in larger papules. The study author wrote that it is possible Demodex mites cause opposite components in host immunity: an immunosuppressive action favoring its own proliferation, and a defense immune response to eliminate the mite.


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T-cell exhaustion possibly diverts the defensive immune response to benefit the mite. The reviewer said that demodicosis and rosacea are indistinguishable, with most patients presenting clinical characteristics of both disorders and no 1 symptom is specific to just 1 of the disorder. It was also noted that topical acaricidal treatment is effective for papulopustules of PPR, but since agents such as benzyl benzoate are not anti-inflammatories, they must be “killing the parasites” which perhaps “confirms the role of the parasite in the development of PPR.”

The reviewer concluded that, “Current data appear to support the pathogenic role of Demodex in PPR, with proliferation of the Demodex mite appearing to be a necessary cause inside a complex network in which multiple co-factors interact to influence disease development.”

Reference

Forton FMN. Rosacea, an infectious disease: why rosacea with papulopustules should be considered a demodicosis. A narrative review. J Eur Acad Dermatol Venereol. July 2022; 36(7):987-1002. doi:10.1111/jdv.18049