What is meningitis? What is encephalitis?
Infections, and less commonly other causes, in the brain and spinal cord can cause dangerous inflammation. This inflammation can produce a wide range of symptoms, including fever, headache, seizures, change in behavior or confusion and, in extreme cases, can cause brain damage, stroke, or even death.
Infection of the meninges, the membranes that surround the brain and spinal cord, is called meningitis. Inflammation of the brain itself is called encephalitis. Myelitis refers to inflammation of the spinal cord. When both the brain and the spinal cord are involved, the condition is called encephalomyelitis.
What causes meningitis and encephalitis?
Infectious causes of meningitis and encephalitis include bacteria, viruses, fungi, and parasites. Many of these affect healthy people. For others, environmental and exposure history, recent travel or immunocompromised state (such as HIV, diabetes, steroids, chemotherapy) are important elements. There are also non-infectious causes such as autoimmune causes and medications.
Meningitis is most often caused by a bacterial or viral infection. It also may be caused by a fungal infection, parasite, a reaction to certain medications or medical treatments, a rheumatologic 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 cause stroke, hearing loss, 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, including the elderly. Persons who have had pneumococcal meningitis often suffer neurological damage ranging from deafness to severe brain damage. There are immunizations available for certain strains of the Pneumococcal bacteria.
Meningococcal meningitis is caused by the bacterium Neisseria meningitides. 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% of cases are fatal, with another 10-15% causing brain damage and other serious side effects. If this is diagnosed, people who come in close contact with the affected individual should be given preventative antibiotics.
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. Certain foods such as unpasteurized dairy or deli meats are sometimes implicated. 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 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 mostly occurs in immunocompromised individuals such as in AIDS patients but can also occur in healthy people Some of these cases can be indolent and smolder for weeks. Although treatable, fungal meningitis often recurs in nearly half of affected persons.
Parasitic causes include cysticercosis, which is common in other parts of the world as well, and cerebral malaria.
There are rare cases of amoebic meningitis, sometimes related to fresh water swimming, which can be rapidly fatal.
Encephalitis can be caused by the same infections listed above. However, up to 60% of cases remain undiagnosed, so this is an active area of research. 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.
Most diagnosed cases of encephalitis in the United States are caused by enteroviruses, herpes simplex virus types 1 and 2, rabies virus (this can occur even without a known animal bite, such as for example due to exposure to bats), or arboviruses such as West Nile virus, 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, more typically causes meningitis, and rarely encephalitis.
Herpes simplex encephalitis(HSE) is responsible for about 10% 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% of cases result from the initial infection with the herpes simplex virus; the majority of cases are caused by reactivation of an earlier infection. Most people acquire herpes simplex type 1 (the cause of cold sores or fever blisters) in childhood so it is a ubiquitous exposure.
HSE due to herpes simplex virus type 1 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. Symptoms can include headache and fever for up to 5 days, followed by personality and behavioral changes, seizures, hallucinations, and altered levels of consciousness. Brain damage in adults and in children beyond the neonatal period is usually seen in the frontal (leading to behavioral and personality changes) and temporal lobes (leading to memory and speech problems) and can be severe.
Type 2 virus (genital herpes) is most often transmitted through sexual contact. Many people do not know they are infected and may not have active genital lesions. An infected mother can transmit the disease to her child at birth, and through contact with genital secretions. 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 (most people do not notice tick bites) and may include headache, fever, nausea, confusion, partial paralysis,coma, and seizures.
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% 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.
Many cases of encephalitis are caused by an autoimmune disorder which may or may not be triggered by an infection.
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 increased risk.
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 have not been given routine vaccines are at increased risk of developing certain types of bacterial meningitis.
Because these diseases can occur suddenly and progress rapidly, 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, nausea/vomiting, double vision, drowsiness, sensitivity to bright light, and a stiff neck; encephalitis can be characterized by fever, seizures, change in behavior, confusion and disorientation, and related neurological signs depending on which part of the brain is affected by the encephalitic process, as some of these are quite focal (locally centered) while others are more global.
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.
Individuals 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, seizures, and memory loss.
Important signs of meningitis or encephalitis to watch for in an infant include fever, lethargy, not waking for feeding, vomiting, body stiffness, unexplained or unusual irritability, 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/weeks (such as recent exposure to insects or animals, any contact with ill persons, recent travel, or preexisting medical conditions and medications list), 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 can be seen in bacterial or fungal meningitis) and white blood cells (elevated white blood cell counts are also a sign of infection). The procedure is done in a hospital and takes about 45 minutes.The individual will most often be placed on antibiotics and an antiviral drug while awaiting the final microbiology results as delay in treatment can be life-threatening.
- Brain 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. If the individual has abnormal results on a neurological examination, often a CT scan is performed to look for brain swelling, hemorrhage, or abscess which if present, could make a spinal tap unsafe.
- 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. Thee is no radiation involved in this test and it gives a much better picture of the actual brain tissue. this may not be available in the emergency setting so a CT scan is usually performed first in very ill individuals. 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 seizures or patterns that may suggest specific viral infections such as herpes virus, and to detect subclinical seizures which may contribute to abnormalities in level of consciousness in critically ill individuals.
How are these infections treated?
Persons who are suspected of having meningitis or encephalitis should receive immediate, aggressive medical treatment. Both diseases can progress quickly and have the potential to cause severe, irreversible neurological damage.
Early treatment of bacterial meningitis is important to its outcome, with antibiotics that can cross the protective blood-brain lining. Appropriate antibiotic treatment for most types of meningitis can reduce the risk of dying from the disease to below 15%.
Infected sinuses may need to be drained. Corticosteroids such as prednisone may be ordered to relieve brain pressure and swelling and to prevent hearing loss that is common in patients with Haemophilus influenza meningitis. Lyme disease is treated with intravenous antibiotics.
Unlike bacteria, viruses cannot be killed by antibiotics; generally there is no specific treatment for viruses except for the herpes virus, which can be treated with the antiviral drug acyclovir. The physician may prescribe anticonvulsants such as dilantin or phenytoin to prevent seizures and corticosteroids to reduce brain inflammation. If inflammation is severe, pain medicine and sedatives may be prescribed to make the person more comfortable.
Acute disseminated encephalomyelitis is treated with steroids. Fungal meningitis is treated with intravenous antifungal medications.
Antiviral drugs used to treat viral encephalitis include acyclovir and ganciclovir.
Anticonvulsants may be prescribed to stop or prevent seizures. Corticosteroids can reduce brain swelling. Individuals with breathing difficulties may require artificial respiration.
Autoimmune causes of encephalitis are treated with additional immunosuppressant drugs and screening for tumors when appropriate.
Individuals should receive evaluation for comprehensive rehabilitation that might include cognitive rehabilitation, physical, speech, and occupational therapy once the acute illness is under control.
Can meningitis and encephalitis be prevented?
Avoid sharing food, utensils, glasses, and other objects with a person who may be exposed to or have the infection. Wash hands often with soap and rinse under running water.
Effective vaccines are available to prevent pneumonia, H. influenza, pneumococcal meningitis, and infection with other bacteria that can cause meningococcal meningitis.
People who live, work, or go to school with someone who has been diagnosed with bacterial meningitis may be asked to take antibiotics for a few days as a preventive measure.
To lessen the risk of being bitten by an infected mosquito or other insect, people should limit outdoor activities at night, wear long-sleeved clothing when outdoors, use insect repellents that are most effective for that particular region of the country, and rid lawn and outdoor areas of free-standing pools of water, in which mosquitoes breed. Do not over-apply repellants, particularly on young children and especially infants, as chemicals such as DEET may be absorbed through the skin.
What is the prognosis for these infections?
Outcome generally depends on the particular infectious agent involved, the severity of the illness, and how quickly treatment is given. In most cases, people with very mild encephalitis or meningitis can make a full recovery, although the process may be slow.
Individuals who experience only headache, fever, and stiff neck may recover in 2-4 weeks. Those with bacterial meningitis typically show some relief 48-72 hours following initial treatment but are more likely to experience complications caused by the disease. In more serious cases, these diseases can cause hearing and/or speech loss, blindness, permanent brain and nerve damage, behavioral changes, cognitive disabilities, lack of muscle control, seizures, and memory loss. These patients may need long-term therapy, medication, and supportive care. The recovery from encephalitis is variable depending on the cause and extent of brain inflammation.
What research is being done?
The National Institute of Neurological Disorders and Stroke (NINDS), a component of the National Institutes of Health (NIH) within the U.S. Department of Health and Human Services, conducts and supports a wide range of research on neurological disorders, including meningitis and encephalitis. Current research efforts include gaining a better understanding of how the central nervous system responds to inflammation and to better understand the molecular mechanisms involved in the protection and disruption of the blood-brain barrier, which could lead to the development of new treatments for several neuroinflammatory diseases such as meningitis and encephalitis. A possible therapeutic approach under investigation involves testing neuroprotective compounds that block the damage that accumulates after the infection, and how the inflammation of meningitis and encephalitis can lead to potential complications including loss of cognitive function and dementia.
Where can I get more information?
For more information on neurological disorders or research programs funded by the National Institute of Neurological Disorders and Stroke, contact the Institute's Brain Resources and Information Network (BRAIN) at:
P.O. Box 5801
Bethesda, MD 20824
Information also is available from the following organizations:
Meningitis Foundation of America, Inc.
1818 El Mirage, AZ 85335
National Meningitis Association
P.O. Box 60143
Ft. Myers, FL 33906
NIAID Office of Communications and Government Relations
National Institutes of Health, DHHS
5601 Fishers Lane, MSC 9806
Bethesda, MD 20892