Herpes viruses enter the brain via the nose

Herpesviruses in the brain trigger serious illnesses

09.08.2011

Herpes viruses can apparently enter the brain through the nose and trigger serious neurodegenerative diseases such as Alzheimer's or Parkinson's. Also, multiple sclerosis (MS) and meningitis and certain forms of epilepsy are caused by the herpes viruses, the US researchers report to Erin Harberts of the National Institute of Neurological Disorders and Stroke in Maryland in the current issue of the journal "Proceedings" the US -Academy of Science.

The US scientists have detected human herpesviruses of type 6 (HHV-6) in the human nasal cavity and have been able to prove that these viruses proliferate actively in certain cells there. According to Erin Harberts, HHV-6 probably uses the cells in the nasal cavity to penetrate through the blood-brain barrier into patients' brains. Similar to some other so-called neurotropic viruses, the HHV-6 apparently reach the brain through the nose. There, they can then favor the occurrence of serious diseases, the US researchers report.

Herpesviruses as the cause of neuronal diseases
It has long been known that herpesviruses can play an essential role in the development of various neurodegenerative diseases. So far, however, it was unclear how the herpes viruses penetrate into the central nervous system, write Erin Harberts and colleagues. In several research steps, the US researchers have now been able to show a possible way of HHV-6 in the brain. First, the scientists analyzed in deceased patients, the spread of herpes viruses in the brain. Harberts and colleagues found that although the viruses can occur in all brain regions, but are mainly found in the olfactory center. In a next research step, the scientists succeeded in detecting the presence of HHV-6 in the nasal mucosa, both in healthy and in MS patients and in persons who had lost their sense of smell.

Propagation of herpesviruses in the nasal cavity
More than 40 percent of the tissue samples taken would have contained the herpesviruses, but no connection with the disease of the subjects was to produce, report Harberts and colleagues. In the final studies, US scientists have also shown that HHV-6 can be replicated in cultures from a specific cell type of the nasal cavity. Harberts and colleagues used the so-called olfactory ensheathing cells (OECs), which promote the growth of new olfactory neurons to breed the herpesviruses in the laboratory. The OECs usually surround the axons of the olfactory neurons, guiding them from the nasal cavity to the brain. The US scientists therefore conclude that the herpesviruses are likely to use the OECs to help them cross the blood-brain barrier and get into the brain as well.

Relatively high risk of getting the herpes virus into the brain
The herpes viruses' pathway to the brain, as described by the US researchers, can have serious consequences for the health of those affected, since the virus can trigger serious illnesses such as multiple sclerosis, meningitis or epilepsy after it enters the nervous system. Moreover, as herpesviruses are relatively prevalent, the risk of viruses crossing the blood-brain barrier seems relatively high, as well as evidence of HHV-6 in 40 percent of tissue samples from the brains of deceased patients. In addition, not only the disease itself but also the treatment of herpes virus infections sometimes quite cumbersome. Although there are numerous preparations on the market that promise immediate help, but their effect can not always convince and for a possible use in the nasal cavity - as suggested by the current study results - seem the previous drugs rather unsuitable. (Fp)

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