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What is meningitis? What is encephalitis?
Infections in the brain and spinal cord can cause dangerous
inflammation. This inflammation can produce a wide range
of symptoms, including fever, headache, or confusion and,
in extreme cases, can cause brain damage, stroke, seizures,
or even death.
Infection of the meninges, the membranes that surround the
brain and spinal cord, is called meningitis and inflammation
of the brain itself is called encephalitis. Myelitis is
an infection of the spinal cord. When both the brain and
the spinal cord become inflamed, the condition is called encephalomyelitis.
What causes meningitis and encephalitis?
Meningitis and encephalitis are usually caused by viruses
or bacteria. Most often, the body’s immune system is
able to contain and defeat an infection. But if the infection
passes into the blood stream and then into the cerebrospinal
fluid that surrounds the brain and spinal cord, it can affect
the nerves and travel to the brain and/or surrounding membranes,
causing inflammation. This swelling can harm or destroy nerve
cells and cause bleeding in the brain.
Meningitis
Meningitis is most often caused by a bacterial or viral
infection. It also may be caused by a fungal infection, a
reaction to certain medications or medical treatments, an
inflammatory disease such as lupus, some types of cancer,
or a traumatic injury to the head or spine.
Bacterial meningitis is a rare but potentially
fatal disease. It can be caused by several types of bacteria
that first cause an upper respiratory tract infection and
then travel through the blood stream to the brain. The disease
can also occur when certain bacteria invade the meninges
directly. The disease can block blood vessels in the brain,
causing stroke and permanent brain damage.
Pneumococcal meningitis is the most common form of meningitis
and is the most serious form of bacterial meningitis. Some
6,000 cases of pneumococcal meningitis are reported in the
United States each year. The disease is caused by the bacterium Streptococcus
pneumoniae, which also causes pneumonia, blood poisoning
(septicemia), and ear and sinus infections. At particular
risk are children under age 2 and adults with a weakened
or depressed immune system. Persons who have had pneumococcal
meningitis often suffer neurological damage ranging from
deafness to severe brain damage.
Meningococcal meningitis, which is caused by the bacterium Neisseria
meningitides, is common in children ages 2-18. Each
year in the United States about 2,600 people get this highly
contagious disease. High-risk groups include infants under
the age of 1 year, people with suppressed immune systems,
travelers to foreign countries where the disease is endemic,
and college students (freshmen in particular) who reside
in dormitories. Between 10 and 15 percent of cases are
fatal, with another 10-15 percent causing brain damage
and other serious side effects.
Haemophilus meningitis was at one time the most common form
of bacterial meningitis. Fortunately, the Haemophilus
influenzae b vaccine has greatly reduced the number
of cases in the United States. Those most at risk of getting
this disease are children in child-care settings and children
who do not have access to the vaccine.
Other forms of bacterial meningitis include Listeria
monocytogenes meningitis, which can cross the placental
barrier and cause a baby to be stillborn or die shortly
after birth; Escherichia coli meningitis, which
is most common in elderly adults and newborns and may be
transmitted to a baby through the birth canal, and Mycobacterium
tuberculosis meningitis, a rare disease that occurs
when the bacterium that causes tuberculosis attacks the
meninges.
Viral, or aseptic, meningitis is the most
common form of meningitis in the United States. This typically
mild and non-lethal disease is usually caused by enteroviruses—common
viruses that enter the body through the mouth and travel
to the brain and surrounding tissues where they multiply.
Enteroviruses are present in mucus, saliva, and feces and
can be transmitted through direct contact with an infected
person or an infected object or surface. Other viruses that
cause meningitis include varicella zoster (the virus
that causes chicken pox and can appear decades later as shingles), influenza,
mumps, HIV, and herpes simplex type 2 (genital herpes).
Many fungal infections can affect the brain. The most common
form of fungal meningitis is caused by the fungus cryptococcus
neoformans (found mainly in dirt and bird droppings). Cryptococcal
meningitis is common in AIDS patients. Although treatable,
fungal meningitis often recurs in nearly half of affected
persons.
Encephalitis
Encephalitis can be caused by bacterial infection and, most
often, viral infections. Several thousand cases of encephalitis
are reported each year, but many more may actually occur
since the symptoms may be mild to non-existent in most patients.
There are two types of encephalitis. Primary encephalitis (also
called acute viral encephalitis) is caused by a direct viral
infection of the spinal cord and brain. The infection may
be focal (located in only one area) or diffuse (located in
many different areas). Secondary encephalitis, also
known as post-infective encephalitis, can result from complications
of a current viral infection. Secondary encephalitis that
results from an immunization or earlier viral infection is
known as acute disseminated encephalitis. This illness often
occurs 2 to 3 weeks following the initial infection.
Most cases of encephalitis in the United States are caused
by enteroviruses, herpes simplex virus types 1 and 2, a bite
from a rabid animal (rabies virus), or arboviruses, which
are transmitted from infected animals to humans through the
bite of an infected tick, mosquito, or other blood-sucking
insect. Lyme disease, a bacterial infection spread by tick
bite, can cause encephalitis.
Herpes simplex encephalitis (HSE) is responsible
for about 10 percent of all encephalitis cases, with a frequency
of about 2 cases per million persons per year. More than
half of untreated cases are fatal. About 30 percent of cases
result from the initial infection with the herpes simplex
virus; the majority of cases are caused by reactivation of
an earlier infection.
HSE due to herpes simplex virus type 1 (which causes cold
sores or blisters around the mouth or eyes) can affect any
age group but is most often seen in persons under age 20
or over age 40. This rapidly progressing disease is the single
most important cause of fatal sporadic encephalitis in the
U.S. The virus is transmitted through contact with an infected
person. Symptoms include headache and fever for up to 5 days,
followed by personality and behavioral changes, seizures,
partial paralysis, hallucinations, and altered levels of
consciousness. Brain damage in adults and in children beyond
the neonatal period is usually seen in the frontal and temporal
lobes and can be severe.
Type 2 virus (genital herpes) is most often transmitted
through sexual contact. An infected mother can transmit the
disease to her child at birth, through contact with genital
secretions, but this is uncommon. In newborns, symptoms such
as lethargy, irritability, tremors, seizures, and poor feeding
generally develop between 4 and 11 days after delivery.
Powassan encephalitis is the only well-documented
tick-borne arbovirus in the United States and Canada. Symptoms
are noticed 7-10 days following the bite and may include
headache, fever, nausea, confusion, partial paralysis, and
coma. Permanent neurologic damage occurs in about half of
all cases and death in about 10-15 percent of all cases.
Four common forms of mosquito-transmitted viral encephalitis
are seen in the United States:
- Equine encephalitis affects horses and
humans. Eastern equine encephalitis also infects
birds that live in freshwater swamps of the eastern U.S.
seaboard and along the Gulf Coast. In humans, symptoms
are seen 4-10 days following transmission and include sudden
fever, general flu-like muscle pains, and headache of increasing
severity, followed by coma and death in severe cases. About
half of infected patients die from the disorder. Fewer
than 10 human cases are seen annually in the United States. Western
equine encephalitis is seen in farming areas in the
western and central plains states. Symptoms begin 5-10
days following infection. Children, particularly those
under 12 months of age, are affected more severely than
adults and may have permanent neurologic damage. Death
occurs in about 3 percent of cases. Venezuelan equine
encephalitis is very rare in this country. Children
are at greatest risk of developing severe complications,
while adults generally develop flu-like symptoms. Epidemics
in South and Central America have killed thousands of persons
and left others with permanent, severe neurologic damage.
- LaCrosse encephalitis occurs most often
in the upper midwestern states (Illinois, Wisconsin, Indiana,
Ohio, Minnesota, and Iowa) but also has been reported in
the southeastern and mid-Atlantic regions of the country.
Most cases are seen in children under age 16. Symptoms
such as vomiting, headache, fever, and lethargy appear
5-10 days following infection. Severe complications include
seizure, coma, and permanent neurologic damage. About 100
cases of LaCrosse encephalitis are reported each year.
- St. Louis encephalitis is most prevalent
in temperate regions of the United States but can occur
throughout most of the country. The disease is generally
milder in children than in adults, with elderly adults
at highest risk of severe disease or death. Symptoms typically
appear 7-10 days following infection and include headache
and fever. In more severe cases, confusion and disorientation,
tremors, convulsions (especially in the very young), and
coma may occur.
- West Nile encephalitis was first clinically
diagnosed in the United States in 1999; 284 people are
known to have died of the virus the following year. There
were 9,862 reported cases of human West Nile disease in
calendar year 2003, with a total of 560 deaths from this
disorder over 5 years. The disease is usually transmitted
by a bite from an infected mosquito, but can also occur
after transplantation of an infected organ or transfusions
of infected blood or blood products. Symptoms are flu-like
and include fever, headache, and joint pain. Some patients
may develop a skin rash and swollen lymph glands, while
others may not show any symptoms. At highest risk are elderly
adults and people with weakened immune systems.
Who is at risk for encephalitis and meningitis?
Anyone can get encephalitis or meningitis. People with weakened
immune systems, including those persons with HIV or those
taking immunosuppressant drugs, are at the highest risk of
contracting the diseases.
How are these disorders transmitted?
Some forms of bacterial meningitis and encephalitis are
contagious and can be spread through contact with saliva,
nasal discharge, feces, or respiratory and throat secretions
(often spread through kissing, coughing, or sharing drinking
glasses, eating utensils, or such personal items as toothbrushes,
lipstick, or cigarettes). For example, people sharing a household,
at a day care center, or in a classroom with an infected
person can become infected. College students living in dormitories—in
particular, college freshmen—have a higher risk of
contracting meningococcal meningitis than college students
overall. Children who do not have access to childhood vaccines
are at increased risk of developing certain types of bacterial
meningitis.
Because these diseases can occur suddenly, anyone who is
suspected of having either meningitis or encephalitis should
immediately contact a doctor or go to the hospital.
What are the signs and symptoms?
The hallmark signs of meningitis are sudden fever, severe
headache, and a stiff neck; encephalitis is characterized
by seizures, stupor, coma, and related neurological signs.
In more severe cases, neurological symptoms may include nausea
and vomiting, confusion and disorientation, drowsiness, sensitivity
to bright light, and poor appetite.
Meningitis often appears with flu-like symptoms that develop
over 1-2 days. Distinctive rashes are typically seen in some
forms of the disease. Meningococcal meningitis may be associated
with kidney and adrenal gland failure and shock.
Patients with encephalitis often show mild flu-like symptoms.
In more severe cases, patients may experience problems with
speech or hearing, double vision, hallucinations, personality
changes, loss of consciousness, loss of sensation in some
parts of the body, muscle weakness, partial paralysis in
the arms and legs, sudden severe dementia, impaired judgment,
seizures, and memory loss.
Important signs of encephalitis to watch for in an infant
include vomiting, body stiffness, constant crying that may
become worse when the child is picked up, and a full or bulging
fontanel (the soft spot on the top of the head).
How are meningitis and encephalitis diagnosed?
Following a physical exam and medical history to review
activities of the past several days (such as recent exposure
to insects or animals, any contact with ill persons, or recent
travel), the doctor may order various diagnostic tests to
confirm the presence of infection and inflammation. Early
diagnosis is vital, as symptoms can appear suddenly and escalate
to brain damage, hearing and/or speech loss, blindness, or
even death.
A neurological examination involves a series of
tests designed to assess motor and sensory function, nerve
function, hearing and speech, vision, coordination and balance,
mental status, and changes in mood or behavior. Doctors may
test the function of the nervous system through tests of
strength and sensation, with the aid of items including a
tuning fork, small light, reflex hammer, and pins.
Laboratory screening of blood, urine, and body secretions can
help detect and identify brain and/or spinal cord infection
and determine the presence of antibodies and foreign proteins.
Such tests can also rule out metabolic conditions that have
similar symptoms. For example, a throat culture may
be taken to check for viral or bacterial organisms that cause
meningitis or encephalitis. In this procedure, the back of
the throat is wiped with a sterile cotton swab, which is
then placed on a culture medium. Viruses and bacteria are
then allowed to grow on the medium. Samples are usually taken
in the physician’s office or in a laboratory setting
and sent out for analysis to state laboratories or to the
U.S. Centers for Disease Control and Prevention. Results
are usually available in 2 to 3 days.
Analysis of the cerebrospinal fluid that surrounds
and protects the brain and spinal cord can detect infections
in the brain and/or spinal cord, acute and chronic inflammation,
and other diseases. In a procedure known as a spinal tap
(or lumbar puncture), a small amount of cerebrospinal fluid
is removed by a special needle that is inserted into the
lower back. The skin is anesthetized with a local anesthetic
prior to the sampling. The fluid, which is completely clear
in healthy people, is tested to detect the presence of bacteria
or blood, as well as to measure glucose levels (a low glucose
level is a sign of bacterial or fungal meningitis) and white
blood cells (elevated white blood cell counts are also a
sign of infection). The procedure is usually done in a hospital
and takes about 45 minutes.
Computer-assisted imaging can reveal signs of brain
inflammation, internal bleeding or hemorrhage, or other brain
abnormalities. Two painless, noninvasive imaging procedures
are routinely used to diagnose meningitis and encephalitis.
- Computed tomography, also known as a CT scan,
combines x-rays and computer technology to produce rapid,
clear, two-dimensional images of organs, bones, and tissues.
Occasionally a contrast dye is injected into the bloodstream
to highlight the different tissues in the brain and to
detect signs of encephalitis or inflammation of the meninges.
CT scans can also detect bone and blood vessel irregularities,
certain brain tumors and cysts, herniated discs, spinal
stenosis (narrowing of the spinal canal), blood clots or
intracranial bleeding in patients with stroke, brain damage
from a head injury, and other disorders.
- Magnetic resonance imaging (MRI) uses computer-generated
radio waves and a strong magnet to produce detailed images
of body structures, including tissues, organs, bones, and
nerves. The pictures, which are clearer than those produced
by CT, can help identify brain and spinal cord inflammation,
infection, tumors, eye disease, and blood vessel irregularities
that may lead to stroke. A contrast dye may be injected
prior to the test to reveal more detail.
Electroencephalography, or EEG, can identify abnormal
brain waves by monitoring electrical activity in the brain
through the skull. Among its many functions, EEG is used
to help diagnose certain seizure disorders, brain damage
from head injuries, specific viral infections such as herpes
virus, and inflammation of the brain and/or spinal cord.
This painless, risk-free test can be performed in a doctor’s
office or at a hospital or testing facility.
To read the rest of this article (including treatment information)
from the National Institute of Neurological Disorders and
Stroke, please click here: http://www.ninds.nih.gov/disorders/encephalitis_meningitis/detail_encephalitis_meningitis.htm
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