Viruses have been implicated in the development of neurodegenerative diseases, such as Alzheimer's, Parkinson's, and multiple sclerosis.
Human herpesvirus-6 (HHV-6) is a neurotropic virus that has been associated with a wide variety of neurologic disorders, including encephalitis, mesial temporal lobe epilepsy, and multiple sclerosis. [Note: HHV-6 has also long been suspected as playing a role in chronic fatigue syndrome (ME/CFS) in conjunction with Epstein-Barr Virus/mononucleosis, and can persist in the brain tissue after evidence of primary infection has disappeared from the blood, according to the HHV-6 Foundation.]
Currently, the route of HHV-6 entry into the CNS [central nervous system – brain and spinal cord] is unknown.
Using autopsy specimens, we found that the frequency of HHV-6 DNA in the olfactory bulb/tract region was among the highest in the brain regions examined. [Note: the olfactory (odor sensing) system includes receptors in the roof of the nose which connect with the olfactory nerve, which terminates in the olfactory bulb (part of the brain), which in turn connects to parts of the cortex and amygdala.]
Given this finding, we investigated whether HHV-6 may infect the CNS via the olfactory pathway.
• HHV-6 DNA was detected in a total of 52 of 126 (41.3%) nasal mucous samples, showing the nasal cavity is a reservoir for HHV-6.
• Furthermore, specialized olfactory-ensheathing glial cells located in the nasal cavity were demonstrated to support HHV-6 replication in vitro.
Collectively, these results support HHV-6 utilization of the olfactory pathway as a route of entry into the CNS.
[Note: As described vividly by Mark Donohoe, MD, in his free book on environmental illness, Killing Us Softly, “the olfactory nerve is less a nerve than it is a misplaced piece of the brain, dangling almost unprotected in the outside world,” and every cell of which is “a card-carrying member of the central nervous system.”]
Source: Proceedings of the National Academy of Sciences USA (PNAS), Aug 8, 2011. doi:10.1073/pnas.1105143108, by Harberts E, Yao K, Wohler JE, Maric D, Ohayon J, Henkin R, Jacobson S. Viral Immunology Section, National Institute of Neurological Disorders and Stroke, Bethesda, Maryland, USA. [Email: firstname.lastname@example.org]