Demodex mites have yet to rise above the rosacea folklore and be proved to be a cause of rosacea. As far as I'm concerned the jury is still out. On the evidence so far, IMHO, more research is needed to prove a link and confirm to what extent symptoms may be related to the presence of demodex.
The NRS has sponsored a couple of studies in the past that look at what role demodex mites might play in rosacea. They themselves are not leaping to any conclusions - "these invisible organisms may be a cause or exacerbating factor in rosacea."
NRS Blog: Possible Role for Mites
So a one line summary is that the bacterium Bacillus oleronius can be isolated from demodex mites, and this then has been shown to produce a response that can be seen as papules and pustules.In the new study, published in the British Journal of Dermatology, the researchers identified Bacillus oleronius as distinct bacteria associated with Demodex mites. When analyzing blood samples using a peripheral blood mononuclear cell proliferation assay, they discovered that B. oleronius stimulated an immune system response in 79 percent of 22 patients with subtype 2 (papulopustular) rosacea, compared with only 29 percent of 17 subjects without the disorder.
It is then tempting to say that because treatments like antibiotics destroy B. oleronius, that this bacteria is the cause of the inflammation. Don't be tempted I say. Wait for proof. There are likely many factors that cause the inflammation of rosacea. I believe that rosacea is multifactorial, and this bacteria sounds too simple an explanation to me. Might it simply cause some inflammation in some sufferers ? that sounds more reasonable to me.
Here are some previous commentary from Rosacea News: if you'd like to read some more.