In 2005 Barry Marshall and Robert Warren received the Nobel Prize in medicine for their discovery that about 75% of peptic ulcer disease was infectious – secondary to infection with H pylori, a bacterium. Earlier studies had shown that viruses could cause certain forms of cancer. Kaposi’s sarcoma was a prominent feature of the weakened immune system cause by symptomatic HIV infection – AIDS.
This work was a jolt to the medical profession’s thinking. If a disease thought to be related to excess gastric acid secretion turned out to be an infectious disease it was obviously possible that many other diseases thought not to have an infectious etiology could have an infectious component.
Alzheimer’s Disease is characterized by the accumulation of amyloid and tau proteins in the brains of afflicted patients. But how or if these proteins cause dementia is not known. New work is focusing on the possibility that this disorder may, at least in part, be infectious. There is a possibility that the herpes simplex virus may play a role in Alzheimer’s in patients genetically predisposed to respond adversely to its presence in the brain. An association between the HSV virus and the apolipoprotein E gene has been suggested as a possible cause of the disease. Obviously, such a causal relationship is at such an early stage that nothing may come of this putative interaction between a virus and a gene variant. But it’s certainly worth further study.
More certain is the association between chronic inflammation and a whole host of diseases including type 2 diabetes and vascular disease in general. A common cause, and an easily preventable one, of chronic inflammation is poor oral hygiene. There was a reason your mother told you to brush and floss regularly. For a good discussion of this issue see Rethinking the Most Common Causes of Death.
Medicine is not a science, though it relies heavily on science. When a doctor has a patient in front of him, he must do the best he can based on the best evidence available. Scientists are not under the same pressure. They can take as much time as necessary to first come up with the right question and then the best answer. The subject can always be re-evaluated. The doctor must proceed with what’s available realizing that the most current evidence often turns out to be inadequate or incorrect. The cause(s) of dementia will doubtless turn out differently from what we now think.