Demodex Mites Resurface In the Rosacea Picture

In a study conducted by Dr. Kevin Kavanagh, Department of Biology, National University of Ireland - Maynooth, and Dr. Frank Powell, consultant dermatologist, Mater Misericordiae Hospital, Dublin.

Bacteria associated with microscopic mites known as Demodex folliculorum are believed to possibly play a role in the development of papulopustular (subtype 2) rosacea, according to the results of a study funded by a National Rosacea Society grant and reported at the 2004 annual meeting of the Society for Investigative Dermatology.

In the completed study, Dr. Kevin Kavanagh and colleagues found that the bacterium Bacillus oleronius stimulated an immune system response, inducing high levels of T-cell proliferation, in 79 percent of patients with subtype 2 rosacea, compared with only 29 percent of patients without the disorder. T-cell proliferation induces an inflammatory response, evident as papules and pustules.

"This indicates that the Bacillus bacteria found in the Demodex mite produce an antigen that could be responsible for the tissue inflammation associated with papulopustular rosacea," Dr. Kavanagh said.

The researchers located the bacteria in Demodex folliculorum, which are normal inhabitants of human skin. Because these microorganisms often occur in much greater numbers in patients with rosacea, researchers have long theorized that they may play a part in the development of the disorder.

The researchers offered several possibilities that may explain how Demodex and bacteria interact to cause inflammation in rosacea. The Demodex mites may carry the pathogenic bacteria into areas of the face susceptible to the changes of rosacea, so that the increased mite density in rosacea patients may result in a higher density of bacteria that produce the papules and pustules. Alternatively, Demodex mites may be attracted to an area of facial skin rich in these bacteria and increase in numbers in this "fertile territory."

Another possibility is that the mites in rosacea patients are infected with these bacteria, which in turn produce stimulatory antigens that trigger the disorder in susceptible patients.

Dr. Kavanagh noted that the potential role for bacteria in causing papulopustular rosacea is supported by the fact that typical treatment for rosacea initially includes oral antibiotics that destroy B. oleronius. Interestingly, he said, antibiotics that are not harmful to these bacteria generally are not effective in the management of rosacea.

Moreover, the possibility that antigens may play a role in disease processes has been demonstrated in other disorders. For example, antigens produced by Streptococcus and Staphylococcus bacteria have been linked with such disorders as psoriasis, food poisoning and toxic shock syndrome.

Dr. Kavanagh and his colleagues are now developing antibodies against the antigen produced by B. oleronius to confirm its presence on the faces of patients with papulopustular rosacea and to define its relationship with Demodex mites.