Facts on File Encyclopedia of Health and Medicine

older children may complain of severe HEADACHE.
Adults often exhibit changes in mental alertness,
cognitive ability, and emotional stability and may
have severe headache. Both children and adults
may have seizures, FEVER, NAUSEA, and VOMITING.

Diminished awareness or loss of con-

sciousness that accompanies or follows

other symptoms of encephalitis is an

indication of serious INFECTION that

requires urgent medical attention.

The diagnostic path includesLUMBAR PUNCTUREto
determine the presence of pathogens or white
BLOODcells, or excessive fluid or increased pressure
in the spinal column, any of which may indicate
infection. Blood tests may show the presence of
certain viruses. Diagnostic procedures such as elec-
troencephalogram (EEG) andCOMPUTED TOMOGRA-
PHY(CT) SCANorMAGNETIC RESONANCE IMAGING(MRI)
can show abnormalities of brain function and
structure that are characteristic of encephalitis.

Treatment Options and Outlook

Mild viral encephalitis generally runs its course
within five to seven days and does not require
treatment beyond ANALGESIC MEDICATIONSsuch as
acetaminophen to relieve fever and headache.
ANTIVIRAL MEDICATIONScan reduce the severity of
symptoms and length of illness for some forms of
viral encephalitis, notably those resulting from
viruses in the herpes family, though have no effect
against encephalitis resulting from arboviruses.
CORTICOSTEROID MEDICATIONSto suppress the inflam-
matory response can reduce intracranial swelling
and pressure that commonly accompanies
encephalitis. Bacterial encephalitis, which is much
less common than viral encephalitis and usually a
secondary infection, requires treatment with
antibiotic medications. Antibiotics are not effective
against viral infections.
Recovery depends on the severity of symptoms
and the causative PATHOGEN. Though viral
encephalitis is generally more mild than bacterial
encephalitis, it can be fatal, particularly in infants,
the very elderly, and people who are IMMUNOCOM-
PROMISED. People who have mild encephalitis
recover completely and without residual compli-

cations. More severe illness may result in perma-

nent brain damage and corresponding cognitive

dysfunction, memory impairment, LEARNING DISOR-

DERS, PARALYSIS, SEIZURE DISORDERS, or speech disor-

ders.

Risk Factors and Preventive Measures

The risk for viral encephalitis is greatest during

times of the year when mosquito and tick activity

is highest, typically May through October in most

parts of the United States. Other risks include liv-

ing in close contact, such as in dormitories and

institutions, and infection elsewhere in the body

that migrates to the brain. Prevention efforts

include public health measures to control mos-

quito populations and individual efforts to mini-

mize exposure to mosquitoes and ticks.

See also COGNITIVE FUNCTION AND DYSFUNCTION;

MEMORY AND MEMORY IMPAIRMENT; MENINGITIS.

Epstein-Barr virus A member of the herpesvirus

family best known for causing the illness infec-

tious mononucleosis. INFECTIONwith the Epstein-

Barr VIRUS, also called human herpesvirus-4

(HHV-4), causes other disease as well and was the

first virus researchers linked with cancer (notably

Burkitt’s lymphoma). Epstein-Barr virus is ubiqui-

tous; it infects more than 90 percent of Americans

by age 25.

As is characteristic of herpesvirus infections,

Epstein-Barr virus causes first an acute illness

(infectious mononucleosis), then retreats into a

state of dormancy and remains in the body as a

latent infection that does not cause illness or

symptoms. B-cell lymphocytes, white BLOODcells

key to ANTIBODY-MEDIATED IMMUNITY, harbor the

latent Epstein-Barr virus. Though the virus does

not change the ability of its host B-cell lympho-

cytes to function within the IMMUNE RESPONSE, it

does alter their DNA such that they become

immortalized—they lose their genetic encoding for

APOPTOSIS, the natural process for cell death.

Only a small percentage of B-cell lymphocytes

contain the virus, so for the most part immune

function continues as normal. A healthy IMMUNE

SYSTEMmaintains a balance between B-cell lym-

phocytes and T-cell lymphocytes (white blood cells

key to CELL-MEDIATED IMMUNITY) that prevents B-

Epstein-Barr virus 323