Over the years, a number of diseases that were previously considered non-communicable have been found to have a microbial component. The role of Helicobacter pylori in ulcer formation is a particularly well-known example. The circulation is a closed system and the blood in healthy organisms was first believed to be a sterile environment. However, there is increasing recognition that blood in healthy organisms is not "steril" as it contains microbes in dormant state.
The presence of a blood bacteria has been associated with a variety of infectious as well as non-infectious diseases. Helicobacter pylori can exist not only in the stomach but also in peripheral blood, where it can contribute to Parkinson's disease and anemia. Individuals infected with Listeria monocytogenes, Salmonella typhimurium and Yersinia pestis become lifelong carriers as the bacteria survive intracellularly. There is also growing evidence that periodontal disease and gingivitis are closely linked to cardiovascular disease, pancreatic cancer, and lung cancer. It has also been proposed that the blood microbiota might represent or contribute to the first step in the development of atherosclerosis and type II diabetes.
Bacteria association with blood cells
Persistent colonization with Helicobacter pylori and Salmonella enterica typhi are usually not clinically apparent. However, even in the absence of clinical symptoms, infection poses some risk to the host. For example, H. pylori induce gastritis with varying degrees of severity. In addition, individuals who are chronically infected with Salmonella enterica typhi have an increased risk of developing hepatobiliary cancer.
It has been established that bacteria is present in almost all of the Alzheimer's disease (AD) and Parkinson's disease (PD) blood samples, in numbers much greater than in those seen in healthy individuals. Both red and white blood cells extend special projections towards the microbiota that might serve as a the mechanism by which the cells "engulf" the bacteria. Both coccoid (round) and bacillary (elongated) bacteria were found in PD whole blood samples, but only coccoid forms in AD whole blood samples.
- The dormant blood microbiome in chronic, inflammatory diseases. Marnie Potgieter et al.
- Helicobacter and Salmonella Persistent Infection Strategies. Denise M. Monack