Encephalitis is an
inflammation of the brain, usually caused by a direct viral infection or a
hypersensitivity reaction to a virus or foreign protein. Brain inflammation
caused by a bacterial infection is sometimes called cerebritis. When both
the brain and spinal cord are involved, the disorder is called
Encephalitis is an
inflammation of the brain that is a reaction of the body's immune system to
infection or invasion. During the inflammation, the brain's tissues become
swollen. The combination of the infection and the immune reaction to it can
cause headache and a fever, as well as more severe symptoms in some cases.
The viruses causing primary
encephalitis can be epidemic or sporadic. The poliovirus is an epidemic
cause. Insect-borne viral encephalitis is responsible for most epidemic
viral encephalitis. The viruses live in animal hosts and mosquitoes that
transmit the disease. The most common form of non-epidemic or sporadic
encephalitis is caused by the herpes simplex virus, type 1 (HSV-1) and has
a high rate of death. Mumps is another example of a sporadic cause.
There are more than a dozen
viruses that can cause encephalitis, spread by either human-to human
contact or by animal bites. Encephalitis may occur with several common
viral infections of childhood. Viruses and viral diseases that may cause
Primary encephalitis is
caused by direct infection by the virus, while secondary encephalitis is due
to a post-infectious immune reaction to viral infection elsewhere in the
body. Secondary encephalitis may occur with measles, chickenpox, mumps,
rubella, and EBV. In secondary encephalitis, symptoms usually begin 5-10
Mosquitoes are carriers to
many types of encephalitis including the Japanese type. The risk of
contracting a mosquito-borne virus is greatest in mid- to late summer when
mosquitoes are most active. The viruses responsible for this disease are
classified as arbovirus and these diseases are collectively called
Herpes simplex encephalitis
is a disease responsible for 10% of all encephalitis cases and is the main
cause of fatal encephalitis. In untreated patients, the rate of death is 70%.
Symptoms may progress
rapidly, changing from mild to severe within several days or even several
hours. The symptoms of encephalitis range from very mild to very severe and
(sleepiness, decreased alertness, and fatigue)
consciousness (drowsiness, confusion, delirium, unconsciousness)
Diagnosis of encephalitis
includes careful questioning to determine possible exposure to viral
sources. Tests that can help confirm the diagnosis and rule out other
tests. These are to detect antibodies to viral antigens, and foreign
fluid analysis (spinal tap). This detects viral antigens
and MRI scan.
brain biopsy (surgical gathering of a small tissue sample)
Choice of treatment for
encephalitis will depend on the cause. Bacterial encephalitis is treated
with antibiotics. Viral encephalitis is usually treated with antiviral
drugs including acyclovir, ganciclovir, foscarnet, ribovarin, and AZT.
Viruses that respond to acyclovir include herpes simplex.
The symptoms of encephalitis
may be treated with a number of different drugs. Corticosteroids are
sometimes prescribed to reduce inflammation and brain swelling.
Anticonvulsant drugs are used to control seizures. A person with
encephalitis must be monitored carefully, since symptoms may change
Encephalitis symptoms may
last several weeks. Most cases of encephalitis are mild, and recovery is
usually quick. Mild encephalitis usually leaves no residual neurological
problems. Overall, approximately 10% of those with encephalitis die from
their infections or complications such as secondary infection. Some forms
of encephalitis have more severe courses, including herpes encephalitis, in
which mortality is 15-20% with treatment, and 70-80% without. Antiviral
treatment is ineffective for eastern equine encephalitis, and mortality is
Permanent neurological consequences
may follow recovery in some cases. Consequences may include personality
changes, memory loss, language difficulties, seizures, and partial
Because encephalitis is due
to infection, avoiding the infection may prevent it. Minimizing contact
with others who have any of the viral illness listed above may reduce the
chances of becoming infected. Most infections are spread by hand-to-hand or
hand-to-mouth contact; frequent hand washing may reduce the likelihood of
infection if contact cannot be avoided.
Mosquito-borne viruses may be
avoided by preventing mosquito bites. Mosquitoes are most active at dawn
and dusk, and are most common in moist areas with standing water.
Minimizing exposed skin and use of mosquito repellents on other areas can
reduce the chances of being bitten.
Vaccines are available
against some viruses, including polio, herpes B, Japanese encephalitis, and
equine encephalitis. Rabies vaccine is available for animals; it is also
given to people after exposure.