For years people thought stomach ulcers were caused by stress until Dr. Barry Marshall and Dr. Robin Warren won the Nobel Prize by proving the bacteria Helicobacter pylori was the primary cause of gastric ulcers. It took them years to convince the medical community of this fact. Dr. Marshall actually had to ingest a flask of the bacteria and develop ulcers to prove this fact, to an unbelieving community of practitioners. He and Dr. Warren won the Nobel Prize for medicine due to this discovery.
Helicobacter pylori is a Gram-negative bacteria that has have been found colonizing the stomach in over 1/2 the people in the world. It can cause chronic active gastritis which can progress to peptic and duodenal ulcers, and gastric cancer, and MALT lymphoma. The person's immune system is unable to clear the infection and it persists unless treated. Luckily, not everyone is negatively effected by the bacteria. The reasons for this are not entirely known at this point.
These bacteria are being implicated in a variety of unusual health conditions. One of them is Alzheimer's disease. There are many research articles that suggest this relationship. One study showed a relationship between Alzheimer's and Helicobacter pylori. Another study showed that eradication of the bacteria induced a improvement in cognition of people with Alzheimer's disease.
It is known that people with H. pylori infection in the stomach lining have low levels of B12 usually. Low levels of B12 are a risk factor for Alzeihmer's disease. H. pylori also creates inflammation and inflammation is also a risk factor for Alzeimer's disease.
These bacteria are not the only critters that may be implicated in Alzheimer's disease. There are significant associations between Alzheimer's disease and a variety of pathogens, including Herpes simplex virus type 1, Cytomegalovirus, and other Herpes viruses, Chlamydophila pneumoniae, spirochetes, and various periodontal microbes. Like Helicobacter pylori, these pathogens are able to evade destruction by the host immune system, leading to persistent infection.
These bacteria and viruses increase the expression of pro-inflammatory molecules and activate the innate and adaptive immune systems. There is evidence that pathogens directly and indirectly induce Alzheimer's pathology, including amyloid-β accumulation, phosphorylation of tau protein, neuronal injury, and apoptosis. Chronic brain infection with Herpes simplex virus-1, Chlamydophila pneumoniae, and spirochetes can result in complex cyclic processes of uncontrolled neuroinflammation leading to neurodegeneration. Infections such as Cytomegalovirus, Helicobacter pylori, and periodontal pathogens have been shown to induce production of systemic pro-inflammatory cytokines that may cross the blood-brain barrier to promote neurodegeneration contributing to Alzeihmer's disease.
Currently treatment for Alzheimer's is ineffective. We need to start looking towards causes of inflammation, be they infectious, environmental or otherwise induced.