Virus linked to temporal lobe epilepsy

Open-access science journal PLoS Medicine published a recent study that suggests that infection with the herpes virus might cause temporal lobe epilepsy in some people.

The study found the virus in the brains of 11 out of 16 patients with temporal lobe epilepsy but not in those with other forms of epilepsy.

Studies that test brain tissue are often done post-mortem, on people who have died, because brain surgery is just too risky for the sake of removing samples for research.

This study is particularly impressive because it studied brain tissue from live patients.

In severe cases of epilepsy that don’t respond to medication, one option is to find which bit of the brain triggers the seizures (the ‘foci’) and surgically remove it.

This is particularly effective in people with mesial temporal lobe epilepsy, a type in which the foci is deep within the temporal lobes (mesial means ‘towards the midline’), usually stemming from disturbance in the hippocampus.

The team examined brain tissue removed in operations on 22 patients, and tested it for the presence of the human herpesvirus 6B (HHV-6B).

This type of herpes infection is incredibly common, more than 90% of the population have it. Normally, it’s completely harmless and just lies dormant in the body.

We don’t really know why, but in some people, it seems to reactivate, and is linked to neurological disorders like multiple sclerosis.

The researchers found that it was present in brain cells called astrocytes from 11 out of 16 patients with mesial temporal lobe epilepsy, but wasn’t present at all in patients with other types of epilepsy.

The image on the right is of a herpes infected astrocyte, the infection is visible due to a green marker.

They also studied one patient in more detail. He had four operations in a row, each of which reduced his seizures, until the final one left him seizure-free.

They found that the herpes virus was present most strongly in the temporal lobe tissue from the first operation, was weakly present in later operations, and wasn’t present in other brain areas.

They also found that infected brain tissue didn’t produce very much of a chemical that transports the key neurotransmitter glutamate across the brain.

If it doesn’t get transported properly, it ‘hangs around’, and because glutamate tends to make brain cells more active, too much could lead to overactivity and seizures.

To test the herpes – glutamate link, the team deliberately infected brain tissue taken from a patient without a previous infection.

In the lab, they discovered that herpes slowed the creation of the transporter chemical for glutamate, providing strong evidence for the link.

The evidence from the lab tests, the single case study, and the 22 patients, provides strong evidence that herpes infection could lead to temporal lobe epilepsy in some people.

This is an important finding because it suggests a cause for the disorder in some people, and provides a clear target which could lead to better treatments and prevention strategies.

What is still not clear is why this usually harmless infection might cause some people severe neurological problems, and remain dormant in others.

Link to PLoS Medicine paper.

8 Comments

  1. Posted July 6, 2007 at 2:51 pm | Permalink

    Very interesting! Gotta repost this one and the one on schizophrenia epidemiology in my Russian language blog..

  2. Posted July 7, 2007 at 3:05 am | Permalink

    Strictly speaking, they don’t call it temporal lobe epilepsy any more. The more recent term is complex partial seizures epilepsy since it isn’t just the temporal lobe that’s involved in those type of seizures. Perhaps other parts of the brain are affected by the virus as well?

  3. Posted July 8, 2007 at 10:29 pm | Permalink

    Acute HHV infection has been associated with febrile seizures in kids. Sometimes febrile seizures progress on to epilepsy (although only a small fraction), and that epilepsy usually has a focus in the temporal lobes.
    Febrile seizures also tend to run in families. If there is a susceptibility locus, that would be a good place to look – families with a strong history of febrile seizures in childhood.

  4. Posted November 7, 2007 at 7:26 pm | Permalink

    Very interesting Post!!!.
    This is in agreement with the view that reactive astrocytes may may be responsable or at least contribute to the progression from acute to chronic epilepsy after different types of brain insult.
    It would be interesting to compare the metabolism and protein expression (glutamate transporter, potassium channesl…) of virally infected astrocytes whith that of reactive astrocytes.
    A post related to this topic can be found in my blog NEURODISORDER.

  5. tony
    Posted August 23, 2010 at 9:58 am | Permalink

    very interesting after being diagnosed with herpes I then had a nocturnal seizure right temporal lobe with tonic clonic S.that was in 1999 today I am having herpes every three months which seems to affect my brain I told my gp but he does nothing about it, So I have reffered myself to a specialist.

    • D. Fowler
      Posted November 10, 2011 at 4:11 am | Permalink

      I have had recurring herpes outbreaks (mouth, face,eye, headache, etc)for many years. I avoid high arginine foods, but it’s hard to avoid stress which also triggers herpes. A year ago I began having nighttime seizures, usually after extreme emotional/physical stress. I have had six this year. A local neurologist isn’t interested in the cause/prevention, just medication, so I am seeing a specialist in January.

      • George Lemi
        Posted August 27, 2012 at 12:30 pm | Permalink

        Thanks D. Fowler for the very interesting post. Your case is similar to mine in that, pon turning mid 30, I started having occassional seizure by collapsing down for about 1 minute when I wake up in mid sleep to go for p! This happened for about 2 years then vanished. When I reached mid 40 I started feeling astrange like mild electric short triking my body. I went to a doctor who did a CT scan and diagonised me to have epilepsy. He subscribed me on a carbamazepine drug which I used for 6 months. This shock vanished and I stopped the medication for about a year. Then I suddenly started having night time epilepsy where I would urinate and bite my toungue sverely unconsiously. My wife says that I snores heavily and jerks my body and immediately go back to sleep, soundly! I went back to the former mediacation, and whenever I use it without fail I can go up to a year without a seizure. It is when I stops when seizre returns within the second month or if I drink strong alcohol.
        I live in Africa where there is shortage of specialists and proper consultants on epilepsy.
        Please, let me know if anyone know whether this could be a virus epilepsy, what type of epilepsy and what I should do to eliminate the problem completely.
        I am now 55 years.
        Thanks.
        Lemi

  6. Carol
    Posted December 25, 2012 at 4:33 am | Permalink

    Interesting. I have crippling Obsessive Compulsive Disorder and Independent Generalized Seizures (complex partial, simple partial, and atonics), and I when tested a couple of years back I had high titers of both parvo and HHV6.


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