Compared to other infectious diseases, encephalitis has a high mortality rate.
When death occurs it is usually a result of the brain swelling (inflammation). The
brain is encased in a hard shell (the skull) and when it swells, it pushes downwards
onto the brainstem. This part of the brain controls the vital functioning of breathing
and heart beat and when the pressure upon it becomes severe it ceases to function.
The illness can be very quickly fatal causing extreme trauma for all the family.
It is difficult to understand why a virus infection in the modern world can have
such devastating consequences.
Many viruses can cause encephalitis it is not the virus that is specific - rather
the fact that it has managed to enter the brain. Usually a blood - brain barrier
prevents viruses entering the brain, why this fails in only a very small number
of people is not known. We are currently funding a research project looking
at possible causes.
Normally the blood-brain barrier prevents any large molecules passing from the blood
into the brain. The barrier is the result of the lining of the blood vessels in
the brain. Blood vessels in the rest of the body are lined by cells which
fit together very loosely allowing easy movement by quite large bodies to and from
the blood. Cells lining blood vessels in the brain fit together very tightly
and most substances have to be actively transported through the cells rather than
passing between them. This normally keeps viruses out.
Once in the brain, the virus enters nerve cells and replicates (makes copies of
itself) thus damaging the cell. The copies spill out and cause the infection.
Infection is the invasion of the body by disease-producing organisms and
the reaction of the tissues to their presence and to the toxins generated by them.
There are a number of ways by which a viral infection of the brain may damage nerve
cells
- viruses can enter nerve cells and utilise components of the cell to replicate (make
copies of itself). This may affect glucose or oxygen metabolism and is serious
enough to kill the cell.
- the characteristics of the cell membrane may be altered, disturbing the electrical
properties of the nerve cell.
- byproducts of the body’s defense against the infection (white blood cells,
the contents of dead nerve cells and disabled viruses) can significantly alter the
fluid surrounding nerve cells and affect their functioning.
- swelling resulting from additional fluid entering the brain can interfere with blood
supply and compress the brain resulting in brain dysfunction.
Written by Elaine Dowell, Encephalitis Society
Last modified: March 2008