Infiltration of the Brain by Pathogens Causes Alzheimer's Disease

Newswise — The possibility of an infectious etiology of chronic diseases, including Alzheimer's disease, has long been debated and is difficult to prove. Following a debate last summer sponsored by the Alzheimer Forum on "Challenging Views of Alzheimer's Disease," researchers from Philadelphia College of Osteopathic Medicine and University of Manchester Institute of Science and Technology were asked to write a summary of the debate "Infiltration of the Brain Causes Alzheimer's disease." Peer-reviewed by individuals who do not totally support this belief, the paper was published in the May/June issue Volume 25, 2004, pgs 619-627 of Neurobiology of Aging.

This paper provides a synopsis of the current evidence of how pathogens, both Herpes Simplex Virus type I and Chlamydophila (Chlamydia) pneumoniae are involved in Alzheimer's disease and concludes that pathogens have the ability to cause late-onset sporadic Alzheimer's disease, by far the most common form of Alzheimer's disease (accounts for >90% of all cases). In addition, this form of Alzheimer's disease does not have associated genetic mutations, but does have genetic susceptibility or risk for individuals with certain genes for apolipoproteins, such as the ApoE e4.

Both Herpes Simplex Virus type I and Chlamydia pneumoniae have been found in AD brain tissues. The presence of one or both of these infections in brain tissue can cause inflammation. Inflammation is considered a major factor in the neurodegeneration seen in AD. While current thought is that amyloid accumulation causes the inflammation, the researchers of this paper believe the infection causes inflammation and possibly glial and nerve cell damage followed by amyloid accumulation and subsequently, more degeneration, which is followed by more inflammation and more damage. Thus, the cycle would initially begin with infection followed by cascading of amyloid and nerve cell damage.

The importance of this work is the realization that chronic infection can result in chronic diseases found in the aged population. While the current research does not yet prove conclusively how infection is causing neurodegeneration, evidence continues to accumulate implicating viruses and intracellular bacteria and other organisms in both neurologic and non-neurologic chronic diseases.

Two authors of this paper, Dr. Brian Balin, Ph.D. and Denah Appelt, Ph.D., Philadelphia College of Osteopathic Medicine, co-authored the paper, "Chlamydia pneumoniae induces Alzheimer's-like amyloid plaques in brains of BALB/c mice," which was published in the March issue of Neurobiology of Aging.