Rosacea – What Causes It? News story overplays suggested connection to skin mites

Just got done reading this: Could Bacteria in Skin Mites Help Cause Rosacea? – US News and World Report.  The article leads off with a bold statement that caught my eye

“Bacteria carried by tiny mites on the skin might be responsible for the common dermatological condition known as rosacea, researchers say.”

This caught my attention because I have been reading up on skin microbes recently and though many have suggested connections between microbes and rosacea as far as I know nobody has shown any causal relationship.  And causation vs. correlation has been on my mind a lot recently.

So I read further and found some suggestive but inconclusive statements that were linked together

  • there are more of these mites on the skin of patients with rosacea than on those without
  • a bacterium (Bacillus oleronius) has been found in the mites and in people w/ rosacea
  • this bacterium can be killed with the same antibiotics that seem to have some success in treating rosacea
  • people with rosacea have an immune reaction to compounds from this bacterium 
  • another bacterium Staphylococcus epidermis also appears in patients w/ rosacea but not patients free of rosacea

And that apparently was it … not very convincing.  Sounds like just a lot of random correlations to me.  So I decided to dig deeper.  And I went to see fi I could find the paper which alas was not linked from the news story.

I googled the journal name “Journal of Medical Microbiology” and got to the web site.  The news article had said the “review paper” had come out August 30th so I clicked on the Papers In Press link and got to the paper.  I browsed the abstract, which seemed somewhat different from the gist of the news story

Rosacea is a common dermatological condition that predominantly affects the central regions of the face. Rosacea affects up to 3% of the world’s population and a number of subtypes are recognized. Rosacea can be treated with a variety of antibiotics (e.g. tetracycline or metronidazole) yet no role for bacteria or microbes in its aetiology has been conclusively established. The density of Demodex mites in the skin of rosacea patients is higher than in controls, suggesting a possible role for these mites in the induction of this condition. In addition, Bacillus oleronius, known to be sensitive to the antibiotics used to treat rosacea, has been isolated from a Demodex mite from a patient with papulopustular rosacea and a potential role for this bacterium in the induction of rosacea has been proposed. Staphylococcus epidermidis has been isolated predominantly from the pustules of rosacea patients but not from unaffected skin and may be transported around the face by Demodex mites. These findings raise the possibility that rosacea is fundamentally a bacterial disease resulting from the over proliferation of Demodex mites living in skin damaged as a result of adverse weathering, age or the production of sebum with an altered fatty acid content. This review surveys the literature relating to the role of Demodex mites and their associated bacteria in the induction and persistence of rosacea and highlights possible therapeutic options.

And then I did what usually causes me much anguish when I am at home – I clicked on the link for the full text, thinking that I would get a paywall.  And low and behold, I got the preprint of the paper.  The paper is quite interesting in many ways with lots of details about these mites I knew nothing about.  It also has a lot of detail on these two bacterial species and why the authors think they are of interest in rosacea etiology.  But no convincing evidence of any kind is presented that there is a causal connection to these bacteria or to these mites.  I leave everyone with the last paragraph of the paper

The pathogenic role of Demodex mites, as well as B. oleronius and S. epidermidis, in the induction and persistence of rosacea remains an unresolved issue. The lack of an immunological response to Demodex mites in healthy skin raises the possibility of localized immunosuppression, facilitating the survival of the mite. Hopefully, the results of further research will bring us closer to understanding the role of microbes in the pathogenesis of rosacea and assist in the development of new and more effective therapies for the treatment of this disfiguring disease.

I agree. Unresolved.

Velasquez-Manoff opinion piece in the NY Times on autism, parasites & inflammation; nice ideas; not enough caveats

There is a very interesting “Opinion” piece in the New York Times today: Immune Disorders and Autism – NYTimes.com.  By Moises Velasquez-Manoff is details some recent work that the author believes relates to autism and a variety of other human ailments with an autoimmune connection.

The general logic/key points seem to be as follows:

  • Some autism cases look like a form of inflammatory diseases with the immune system overactive (inflammation on high, anti-inflammation on low, or some combination thereof)
  • Infection of a mother during pregnancy increases the risk of having a child with autism.
  • In animal models, inducing inflammation in the mother (even without an infection) leads to an increased risk of behavioral “problems” in her offspring
  • Inflammatory and/or autoimmune diseases (e.g., asthma) have increased in incidence along with autism.
  • If a mother has automimmune or inflammatory diseases such as rheumatoid arthritis celiac disease she has a higher risk of having a child with autism.  Similarly if a mother has allergies or asthma during the second trimester, there is a higher risk of having children with autism.  
  • Many automimmune and inflammatory disorders and autism are all more prevalent is the developed world.
  • The developed world is generally cleaner that the developing world.  
  • There are many fewer parasites in people in the developed world.
  • Parasites are known to suppress inflammation.
  • Therefore, we may be able to stop/limit autism, asthma, and other inflammatory diseases by purposefully infecting people with parasites from our evolutionary past. 

Now, personally, I like the general hypothesis here.  It makes complete sense.  But alas, it is suffers from this issue that is spreading almost as fast as these diseases – a lack of a discussion of the distinction between correlation and causation.  I have been obsessing about this a bit recently with studies of the microbiome.   Overall, I do like this current article.  It mixes human epidemiological studies with controlled animal studies with discussion of conceptual models.  But alas there is really no discussion of the challenges if disentangling correlations vs. causation. And I think it is a bit dangerous in the latter parts with the jump to potentially curing these various ailments by purposeful infection with parasites.  Again, I like the idea.  But a few caveats would have been nice.  I am glad it was marked as an opinion piece but even when one states an opinion about a medical issue, one can still say “there are reasons why this might not be true .. such as …”.  Too bad that wasn’t done here.

UPDATE – Emily Willingham has written a VERY detailed critique of the article that I think everyone interested in anything related to this topic should read: Emily Willingham: Autism, immunity, inflammation, and the New York Timeswww.emilywillinghamphd.com.