Meningitis and Encephalitis
- Also Known As:
- Spinal Meningitis
- Meningococcal Meningitis
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What are meningitis and encephalitis?
Meningitis is an inflammation of the three membranes that cover the brain and spinal cord (the meninges). Encephalitis is an inflammation of the brain. Meningoencephalitis is an inflammation of both the brain and the meninges.
The meninges are layers of tissue that protect the central nervous system, which is comprised of the brain and the spinal cord. The central nervous system is also cushioned and protected by the…
Meningitis is an inflammation of the three membranes that cover the brain and spinal cord (the meninges). Encephalitis is an inflammation of the brain. Meningoencephalitis is an inflammation of both the brain and the meninges.
The meninges are layers of tissue that protect the central nervous system, which is comprised of the brain and the spinal cord. The central nervous system is also cushioned and protected by the watery fluid called cerebrospinal fluid (CSF) that surrounds the brain and flows between the meninges, in the spaces within the brain called ventricles, and along the spinal cord.
Meningitis and encephalitis result from infections of the central nervous system caused by a bacterium, virus, fungus, or parasite. These infections can be acute or chronic, and their severity can range from mild and self-limited to fatal. Their associated inflammation and swelling increase pressure on the brain and nerve tissue. This can hinder, or permanently damage, the function of nerves and the body systems that they control. Rarely, certain drugs can cause meningitis, and autoimmune disease can sometimes cause encephalitis.
Meningitis and encephalitis can disrupt the blood-brain barrier that separates the brain from circulating blood and regulates the distribution of substances between the blood and CSF. The blood-brain barrier helps keep large molecules, toxins, and most blood cells away from the brain. With the disruption of this barrier, white and red blood cells, immune system chemicals, toxins, increased amounts of protein, and the microorganism causing the inflammation may be found in the CSF. CSF is a clear, watery liquid that normally flows freely around the brain and spinal cord. With meningitis and encephalitis, the flow of CSF may slow or become obstructed, which can increase CSF pressure, increase pressure on the brain and spinal cord, and decrease blood flow to the brain.
About Meningitis and Encephalitis
Causes of Meningitis
Most cases of meningitis are due to a bacterial or viral infection, but it rarely may also be caused by certain cancers, injuries, parasites, or fungal spores in the environment. Bacterial meningitis can be life-threatening, but there are vaccines to prevent four of the five known types of bacterial meningitis. The infection may originate within the meninges (primary) or spread from an infection site located in another part of the body (secondary).
Viral meningitis, also called aseptic meningitis, is the most common form of meningitis in the United States, according to the Centers for Disease Control and Prevention. It is usually mild to moderate in severity and will usually resolve without treatment (self-limited).
- Enteroviruses are the most common cause of viral meningitis. Though enteroviruses are very common, they usually cause no symptoms or illness in most cases.
Less common causes include:
- Herpes simplex virus (HSV)
- Epstein-Barr virus (EBV)
- Varicella-zoster virus (VZV)—the cause of chickenpox and shingles
- Arboviruses—viruses spread by mosquitoes
Bacterial meningitis is generally considered a medical emergency. Acute cases can arise suddenly, with symptoms worsening within hours to a couple of days. Rapid identification and treatment is crucial. Untreated bacterial meningitis is usually fatal. While this condition can be caused by many different types (species) of bacteria, the most common causes are:
- Streptococcus pneumoniae – called pneumococcal meningitis; it is currently the most common form of bacterial meningitis in the U.S. It can also cause pneumonia, blood infections (septicemia), and ear and sinus infections. Infants under 2 years old, people with compromised immune systems, and the elderly are at greatest risk for it.
- Neisseria meningitidis – called meningococcal meningitis; it is highly contagious; people who are at risk include college students, infants, children younger than 1 year old, international travelers, and people with weakened immune systems.
- Haemophilus influenzae type b – once the most common cause of bacterial meningitis, its incidence has decreased in the U.S. because of widespread vaccination of children.
- Other causes include Listeria monocytogenes as well as Group B streptococcus and Escherichia coli, which may cause meningitis in a newborn when the mother passes the infection to her baby during delivery. Pregnant women are screened for Group B strep late in their pregnancy to determine whether there is risk of passing the infection to their babies.
Chronic meningitis is an infection that lasts for more than 4 weeks. It may be caused by microbes such as Mycobacterium tuberculosis, which causes tuberculosis, by Treponema pallidum, which causes syphilis, and by fungi.
Fungal meningitis, though rare, is most commonly seen in immune-compromised patients, such as those with AIDS, but may affect anyone.
- The most common cause is Cryptococcus neoformans (cryptococcal meningitis), thought to be contracted through inhaling dirt contaminated with bird droppings.
Other causes include:
- Coccidioides immitis
- Histoplasma capsulatum
- Candida species
Fungal meningitis is not contagious; it is not spread from person-to-person but occurs when an individual with a weakened immune system inhales spores from the environment. (For more, read the article on Fungal Infections.)
Parasitic meningitis is rare and can be lethal. One example is an infection caused by the free-living amoeba, Naegleria fowleri, a single-cell parasite, which can be found in warm water lakes and rivers. Infection occurs when the parasite enters the respiratory system through the nose of a person swimming in contaminated water. Another example is infection caused by the Schistosomaparasite. This type of infection does not occur in the U.S. but is common in other areas of the world such as Africa, South America, and South China.
Causes of Encephalitis
Encephalitis is an acute infection of the brain characterized by fever, headache, and an altered state of consciousness, with or without seizures. Most cases of encephalitis are caused by viruses. They may also be limited to a single location (focal) or diffuse throughout the brain (generalized). Each year there are several thousand cases reported but, according to the National Institute of Neurological Disorders and Stroke, there are probably many more cases with minimal to mild symptoms that occur but are not documented.
Viral encephalitis may be caused by a variety of viruses including:
- Herpes simplex virus
- The rabies virus (from an animal bite)
- Arboviruses – those spread primarily by infected mosquitoes but also by a few ticks
Most people who are infected have mild to moderate symptoms. Only a very small percentage of people develop encephalitis.
In the United States, West Nile virus is the most common cause of arbovirus encephalitis. Other more rare U.S. arboviruses are distributed geographically. Throughout the world, different types of arbovirus-related encephalitis may predominate. Types of encephalitis caused by arboviruses include:
- West Nile encephalitis – about one in 5 people infected with West Nile virus will develop fever with other symptoms and less than 1% will develop severe illness, according to the Centers for Disease Control and Prevention (CDC).
- Western equine encephalitis – per the CDC, about 3% of those affected die; illness is more severe in infants than adults.
- Eastern equine encephalitis – though this is a rare illness with only a few cases in the U.S. each year, it tends to be one of the most severe; the CDC estimates that about a third of those with the infection will die and many survivors will suffer brain damage.
- LaCrosse encephalitis – found in the upper Midwest, mid-Atlantic, and southeastern states; most severe cases occur in children less than 16 years of age, according to the CDC.
- St. Louis encephalitis – a rare infection, most cases occur in eastern and central states in the U.S.; illness is most severe in the elderly.
Other arboviruses that may be seen in other parts of the world include:
- Japanese encephalitis – found naturally (endemic) in Asia and is associated with rural farming areas; a vaccine to prevent infection is available.
- Venezuelan equine encephalitis – very rare in the U.S.; has killed thousands of people in South American epidemics.
Viral encephalitis may also be seen as a secondary condition that occurs a few weeks after a viral illness.
Bacterial, fungal, and parasitic encephalitis are very rare. Bacterial meningoencephalitis may develop from the bacteria that cause meningitis. Tick-transmitted Lyme disease may cause bacterial encephalitis. Toxoplasma gondii, a parasite associated with cats, can cause parasitic encephalitis in some people with weakened immune systems.
Signs and Symptoms
- Severe persistent headache
- A stiff neck
- Sensitivity to light
- Mental changes
Other symptoms may include confusion, nausea, vomiting, a red or purple rash, and seizures. An elderly person may be lethargic and show few other signs. People with weakened immune systems may have atypical symptoms. Infants may be irritable and cry when they are held, vomit, have body stiffness, have seizures, refuse food, and have bulging fontanels (the soft spots on the top of the head).
Encephalitis symptoms may also include neurological problems such as difficulty with hearing or speech, loss of sensation, partial paralysis, seizures, hallucinations, muscle weakness, changes in personality, and coma.
Complications and Prognosis
The outcome of those with meningitis and encephalitis depends on the specific cause of the condition, the severity, the person’s health and immune status, and how quickly the condition is identified and treated. Those with mild cases may recover fully within a few weeks or may have persistent or permanent complications.
As many as 15-25% of newborns and 15% of other patients with bacterial meningitis die, even when treated appropriately and rapidly. Up to 15-25% of those who survive may have neurological complications (sequelae), including accumulation of fluid within the brain (hydrocephalus), deafness, blindness, periodic seizures, and/or some degree of impaired thinking processes. These complications may occur at any age, but newborns are at the highest risk.
To investigate possible meningitis or encephalitis, healthcare practitioners start with a physical examination and a medical history. This examination may occur in the emergency room as symptoms may suddenly appear and rapidly worsen over several hours to a couple of days.
The healthcare practitioner will ask about recent illnesses, exposure to animals, mosquitoes, or ticks, contact with other people who have become ill, recent travel – especially outside of the United States, and recent activities. The healthcare practitioner will note the presence or absence of signs and symptoms frequently associated with meningitis and encephalitis. Neurological examinations may be performed to assess the status of the patient’s nervous system, sensory and motor function, coordination, vision, hearing, strength, and mental status.
Laboratory tests are performed to detect, identify, evaluate, and monitor meningitis and encephalitis. These tests are performed in order to:
- Distinguish these infections from other conditions with similar symptoms
- Determine the cause, whether bacteria, viruses, fungi, or parasites, as rapidly as possible to start and guide treatment
- Evaluate the affected person’s general state of health, immune system status, current signs and symptoms, and current complications to guide symptom relief and to minimize inflammation and neurological or brain damage
- Where possible, determine the infection’s source; this is especially important when the microbe causing the infection may be spread to others and may be a public health concern.
Depending on the suspected cause, samples may be sent to local or state public health laboratories for testing.
Cerebrospinal fluid (CSF) analysis. This is a primary diagnostic tool for encephalitis and meningitis. CSF analysis is a group of common tests, and a wide variety of other tests, that can be ordered and performed on a sample of CSF. It is collected using a procedure called a lumbar puncture or spinal tap.
Initial CSF tests—The initial basic set of CSF tests that are often performed with suspected infections of the central nervous system include:
- Physical characteristics: normal CSF appears clear and colorless. The appearance of the sample of CSF is usually compared to a sample of water. In infections, the initial pressure of CSF during collection may be increased and the sample may appear cloudy due to the presence of white blood cells (WBCs) or microorganisms.
- CSF protein: only a small amount is normally present in CSF because proteins are large molecules and do not cross the blood/brain barrier easily. Increases in protein are commonly seen with meningitis, brain abscess, and neurosyphilis.
- CSF glucose: normal is about 2/3 the concentration of blood glucose. Glucose levels may decrease when cells that are not normally present use up (metabolize) the glucose. These may include bacteria or cells present due to inflammation (WBCs).
- CSF total cell counts: WBCs may be increased with central nervous system infections.
- CSF WBC differential: small numbers of lymphocytes, monocytes (and in neonates, neutrophils) are normal in a sample of CSF. There may be:
- An increase in neutrophils with a bacterial infection
- An increase in lymphocytes with a viral infection
- Sometimes an increase in eosinophils with a parasitic infection
- CSF Gram stain for direct observation of microbes
- CSF culture and sensitivity for bacteria, fungi, and viruses
Additional or follow-up CSF tests—If any of the initial tests are abnormal, then additional infectious testing may be ordered. This may include one or more of the following:
- Detection of viruses by molecular tests (polymerase chain reactions, PCR) – detection of viral genetic material (DNA, RNA) such as West Nile virus, herpes, and enteroviruses
- CSF Cryptococcal antigen – to detect a specific fungal infection
- Other CSF antigen tests – depending on which organism(s) are suspected
- Specific CSF antibody tests – depending on which organism(s) are suspected
Less commonly ordered CSF infectious diseases tests include:
- CSF AFB smear and culture (when tuberculosis is suspected) – positive with tuberculosis and with other mycobacteria
- CSF Molecular tests to detect Mycobacteria tuberculosis
- CSF syphilis testing (VDRL) – positive with syphilis that has infected the brain (neurosyphilis); negative does not rule out condition
Several other types of CSF testing may occasionally be ordered to help distinguish between viral and bacterial meningitis:
- CSF lactic acid – often used to distinguish between viral and bacterial meningitis; the level will usually be increased with bacterial and fungal meningitis while it will remain normal or only slightly elevated with viral meningitis.
- CSF lactate dehydrogenase (LD) – used to differentiate between bacterial and viral meningitis
- CSF C-reactive protein (CRP) is an acute phase reactant and is elevated with inflammation; it is markedly increased with bacterial meningitis. Since it is very sensitive even with early bacterial meningitis, it is often used to distinguish between bacterial and viral meningitis.
Laboratory tests on samples other than CSF—may be ordered along with or following CSF testing and may include:
- Blood glucose, protein, CBC (complete blood count) – to evaluate and to compare with CSF levels
- Procalcitonin – growing evidence suggests that measuring blood levels of procalcitonin is useful in distinguishing bacterial from viral meningitis; a high blood level is a strong indication of bacterial meningitis.
- Tests for antibodies in blood for a variety of viruses, such as arboviruses, in particular West Nile virus, if there is a four-fold rise in the titer of the antibody between two samples collected about a month apart, then it indicates a recent infection by that microorganism.
- Molecular tests that directly detect viruses in blood
- Blood cultures may be ordered to detect and identify bacteria in the blood.
- Cultures of other parts of the body may be performed to detect the source of the infection that led to meningitis or encephalitis.
- CMP (comprehensive metabolic panel) – tests that evaluate organ function
Imaging tests may be performed to look for signs of brain inflammation or abnormalities but may be unremarkable with encephalitis. Brain damage, tumors, bleeding, and abscesses may be detected. Tests may include:
- CT (computed tomography)
- MRI (magnetic resonance imaging)
- EEG (electroencephalography) – to detect abnormal brain waves
For additional details on these imaging tests, visit RadiologyInfo.org.
Treatment and Prevention
Treatment for encephalitis, meningitis, and meningoencephalitis is targeted to the cause of the infection and inflammation while minimizing tissue damage and complications and relieving patient symptoms. Bed rest in a dark quiet room, fluids, pain relief for head and body ache, anti-inflammatory drugs, anti-seizure medications, sedatives, and anti-nausea agents may be prescribed. Corticosteroids may be given in some cases to help reduce tissue and brain swelling.
Treatment for bacterial causes
Acute bacterial and fungal meningitis and encephalitis are considered medical emergencies. Bacterial infections are frequently treated with a broad-spectrum antibiotic as soon as, or even before, the cause is positively identified. This therapy may then need to be modified once culture results identify the specific bacteria and its susceptibility to antimicrobial agents. Antibiotics chosen must be able to pass through the blood-brain barrier and reach sufficient concentration in the CSF. They may be administered intravenously and reach high levels in the blood. Patients are monitored for signs of drug toxicity and for organ function. Depending on the type of bacteria and the state of the patient’s immune system, treatment may need to be continued for weeks, months, or even years.
Medical procedures are sometimes necessary to drain infected abscesses or sinuses. These procedures may need to be repeated.
Treatment for viral causes
Many cases of viral encephalitis and meningitis may be mild to moderate in severity, self-limited, and only require monitoring, rest, and relief of symptoms. People with more severe cases may require hospitalization. For viral encephalitis due to herpes or varicella-zoster viruses (the cause of chickenpox and shingles), healthcare practitioners may prescribe an antiviral drug such as acyclovir. People with HIV infections are treated with highly active antiretroviral therapy (HAART).
Treatment for fungal causes
Fungal infections are usually treated with intravenous (IV) anti-fungal drugs. Treatment may continue for an extended period of time. Patients with compromised immune systems may have to continue oral therapy indefinitely to prevent the infection from recurring.
Treatment for parasitic causes
Acute parasitic meningoencephalitis caused by the amoeba Naegleria fowleri is frequently fatal because there are no antimicrobial drugs proven effective to treat this infection. Infections with Toxoplasma and other parasitic agents may resolve with appropriate anti-parasitic drugs.
There are vaccines available for:
- Haemophilus influenzae type b—widespread vaccination of children in the U.S. has drastically reduced the incidence of Haemophilus influenzae type b. For details, see the CDC page on Hib Vaccination.
- Streptococcus pneumoniae (pneumococcal meningitis)—see the CDC page on Pneumococcal Vaccination.
- Neisseria meningitidis (meningococcal meningitis)—see the CDC page on Meningococcal Vaccination.
Those with close contact to someone who has meningococcal meningitis may be prescribed antibiotics for a few days to decrease their risk of developing a full-blown infection.
Risk of infection caused by an arbovirus can be minimized by limiting exposure to mosquitoes and ticks, limiting outdoor activities at night, wearing long-sleeved clothing, using insect repellents, and eliminating freestanding water around the home.
1. Are meningitis and encephalitis always caused by infections?
Very rarely, meningitis and encephalitis may be due to a non-infectious cause. Examples include an autoimmune disorder that targets components of the nervous system, a reaction to a drug treatment, or certain cancers.
2. Can other conditions have similar symptoms?
Other serious conditions can cause some of the same symptoms as meningitis and encephalitis but have different causes and treatments. These include a brain abscess, brain lesion, drugs, trauma, or subdural empyema (a collection of pus in the space between the dura mater and arachnoid layers of the meninges).
3. Do meningitis and encephalitis start in the brain?
Meningitis can be caused by an infection in the blood or an infection in close proximity to the brain, such as an ear infection, that allows the microbes to enter the CSF, or head trauma that allows bacteria in the sinuses to cross the blood-brain barrier. Encephalitis can be caused by infections that originate in the respiratory tract, gastrointestinal tract, or the blood that can spread to the central nervous system.
4. Is meningitis contagious?
It depends on the microbe that is causing meningitis. People exposed to someone with meningococcal meningitis may be prescribed antibiotics for a few days to minimize their chance of developing it. There are vaccinations available for Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis that are the most common causes of bacterial meningitis and can be transmitted to others in respiratory secretions.
5. Once I have had meningitis or encephalitis, can I get it again?
It is possible to acquire this type of infection again. Some people with weakened immune systems may need to continue their antimicrobial therapy indefinitely to prevent recurrence.
Sources Used in Current Review
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