While the exact pathology of rosacea is not completely understood or widely agreed upon, recent studies suggest that chronic inflammation likely plays a role in many of the symptoms associated with this disease.
Background
Rosacea is a chronic disorder of still unknown cause that affects an estimated 14 million Americans.1 Rosacea often initially presents itself with transient flushing and redness of the cheeks, nose, forehead and chin, but it may also involve other areas of the body, including the ears, neck, and chest. With time the transient flushing becomes more frequent, the transient redness tends to become more persistent, and papules, pustules, and visible blood vessels called telangiectasias may also appear. Facial swelling, or edema, also often accompanies rosacea, as do burning or stinging sensations of the affected areas. In addition, many people with rosacea often also have the concomitant chronically irritated eye and eyelid symptoms of ocular rosacea and blepharitis.2
The exact pathology of rosacea is not completely understood or widely agreed upon, but recent studies suggest that chronic inflammation likely plays a role in many of the symptoms associated with this disease. And the chronic inflammation and blood vessel involvement in this disorder may well point to involvement of gram-negative bacteria, or more particularly their endotoxins, which have been shown to elicit similar response upon entry into the bloodstream.
While several gram-negative bacteria, including H. pylori and B. oleronius (found in Demodex folliculorum) have been associated with rosacea in the past, they have not been shown to enter the bloodstream, and thus they are unlikely to play anything more than a secondary role in the disease. Chlamydia pneumoniae, however, has been associated with rosacea in one small study, and studies in other inflammatory diseases in which it is being studied closely indicate that it is quite capable entering and persisting in the bloodstream, as well as producing the type of chronic inflammatory response that has been associated with rosacea. This evidence suggests the potential for C. pneumoniae's involvement in rosacea, at least secondarily.
Evidence
Although the exact pathology of rosacea is still unknown, recent studies suggest that chronic inflammation likely plays a role in many of the symptoms associated with the disease. Supporting the role for chronic inflammation is the host of elevated proinflammatory cytokines (TNF-a, IL-1B), matrix metalloproteinases (MMP-1, MMP-3, and MMP-9), nitric oxide (NO), and reactive oxygen species (ROS) that have been associated with rosacea in recent studies.3 Rosacea has been associated with elevated vascular endothelial growth factor (VEGF) in recent studies as well.4
It is important to note that the discovery of these elevated inflammatory mediators in rosacea may suggest important clues to an underlying disease etiology when comparing them as a whole to other known pathologies. And indeed, the elevated cytokines, MMPs, VEGF, NO and ROS associated with rosacea, match closely with the known pathology of early gram-negative sepsis, an infection of the bloodstream caused by toxin-producing bacteria.5
In fact, endotoxins, or rather lipopolysaccharides (LPS), portions of the outer membrane of gram-negative bacteria, are widely known to induce a variety of inflammatory responses, ranging from mild to severe inflammation (and death), depending on the virulence of the bacteria endotoxins themselves.6 Recent studies suggest as well that vascular endothelial growth factor (VEGF) itself may actually be a key biomarker for sepsis.7
While gram-negative bacteria such as H. pylori and even B. oleronius (found in Demodex folliculorum) have been associated with rosacea in past studies, since these bacteria have not been shown to enter the bloodstream, one would not expect them to produce pathology similar to early sepsis.8 So looking at other inflammatory diseases for clues relating to associated gram-negative bacteria, one such pathogen, Chlamydia pneumoniae, stands out for its association with many inflammatory diseases, including Atherosclerosis, Multiple Sclerosis, Asthma, Alzheimer's and other inflammatory disorders.9
Interestingly, one small study has linked C. pneumoniae with rosacea directly, detecting serum antibodies of C. pneumoniae in 8 of 10 patients with rosacea and detecting C. pneumoniae specimens in 4 of 10 cheek biopsy.10 Other studies suggest that infection with C. pneumoniae can lead to pustular rashes (acute generalized exanthematous pustulosis) and increased VEGF production, as in the case with wet age-related macular degeneration.11,12 These of course are most likely caused as by-products of the chronic inflammation associated with this pathogen, but I point them out since papule and pustule rashes and increased VEGF production are symptoms of rosacea.
Persistent C. pneumoniae infection of epithelial cells has been shown to produce chronic blood vessel inflammation, resulting in production of a host of cytokines and growth factors such as those found in rosacea as well as promoting a "foci of inflammatory responses in addition to promoting cellular proliferation, tissue remodeling and healing processes".13 And additional studies suggest that chlamydiae, while classified as gram-negative bacteria due to their outer LPS coating, are actually a distinct group of eubacteria, with a unique multi-form, intracellular and extracellular development cycle, allowing them to change between forms and promote the persistent infection that may lead to chronic inflammatory disease.14
Another clue potentially linking rosacea with C. pneumoniae involves recent studies in the anti-microbial peptides, cathelicidins, and their activity in rosacea. These recent studies have identified unusually high levels of kallikrein activated cathelicidins in rosacea and suggest that these two substances may be in part responsible for producing the papules and pustules associated with rosacea as well as in promoting the angiogenesis associated with the disease.15,16,17 Some additional studies have shown too that C. pneumoniae seems to invoke unusually high levels of cathelicidin activity and that endotoxins in general activate the kallikrein-kinin system.18,19 Intriguingly, still other studies suggest that cathelicidins seem to be ineffective in clearing C. pneumoniae infection.20 Potentially this is due to C. pneumoniae's ability to revert between forms, effectively evading the immune response. If this were correct then a C. pneumoniae infection, with the resulting ineffective yet elevated levels of activated cathelicidins, could indeed explain the unusual cathelicidin activity found in rosacea.
Dr. Charles Stratton, MD, at Vanderbilt University, in a recent interview, 21 summarized his observations of some of the emerging research on C. pneumoniae. He noted how C. pneumoniae crosses from the lungs to the bloodstream via infected macrophages. The spore-like Elementary Bodies (EB's) then circulate in the bloodstream to infect other organs throughout the body, including the liver, bone marrow, spleen, kidneys and skin.21 Potentially this might explain how C. pneumoniae, whose initial entry into the body is via the respiratory system, might arrive in the skin to cause rosacea. This may explain too the discovery of C. pneumoniae in cheek biopsy of rosacea as in the study discussed above.
Conclusion
In summary, Chlamydia pneumoniae may be involved at least secondarily in the etiology of rosacea. C. pneumoniae is a persistent, gram-negative bacteria known to enter and exist in the epithelial cells of the bloodstream, and it is known to produce the type of chronic inflammation that can be found in rosacea. Studies suggest C. pneumoniae may be involved with the etiology of many other inflammatory diseases, and intriguingly, a small study suggests a potential link with rosacea itself. Combined, this evidence would suggest more study related to C. pneumoniae's potential involvement in rosacea is necessary.
References
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