Nose takes virus up to brain

Researchers in the US found that the nose can be a portal for herpes virus-6 (HHV-6), a member of herpes viruses family, which is linked to brain disorders such as multiple sclerosis, encephalitis and a form of epilepsy.

It also causes roseola, a disease common among infants that leads to high fever and skin rash, LiveScience reported.

“This is a virus that we’ve all been exposed to, that we all pretty much acquired in childhood,” said researcher Steven Jacobson, a neurovirologist at the National Institute of Neurological Disorders and Stroke in Bethesda, Maryland. “Most of the time it’s utterly benign.”

The way this virus entered the brain had remained a mystery, as the seat of our intelligence is largely protected by the so-called blood-brain barrier, which filters out many germs and drugs.

However, researchers had known that other viruses, such as influenza and rabies, apparently could use the sensory network hooked up to the nose as a kind of highway into the central nervous system.

To see how HHV-6 enters the brain, scientists analysed tissue samples from autopsies, including a patient who had multiple sclerosis. Although viral DNA was seen throughout the brain, it was found largely in the olfactory bulb, the brain region involved in detecting odours.

In addition, the researchers found DNA from HHV-6 in nasal mucus samples from healthy people, those suffering a loss of smell, and people with multiple sclerosis.

This suggests the nasal cavity might harbour the virus in both healthy and diseased individuals, the team reported in the Proceedings of the National Academy of Sciences.

Moreover, in experiments, the scientists demonstrated that HHV-6 could infect lab-grown versions of the olfactory ensheathing cells, which help olfactory neurons grow and establish connections in the brain.

The researchers believe the virus might use these cells as a bridge across the blood-brain barrier, the first time scientists had evidence these cells could be a route of infection.

“Now researchers can start looking to see if other viruses might use this route as well,” Jacobson said.

The researchers cautioned that while this virus might help trigger brain disorders, it was not necessarily the primary cause. “We may all have it, but some might have a special genetic susceptibility to it, or maybe there’s an environmental trigger that causes neurologic disease to then occur,” Jacobson said.

Further studies could also investigate whether this virus has any effect on behaviour. “It all depends on where this virus goes in the brain,” Jacobson said.

With the new information, researchers could then look for therapies against this virus.