Meningitis and Encephalitis

Meningitis and encephalitis are serious health conditions that cause swelling and irritation in and around the brain. Most but not all are caused by viral infections.

Emergency Information

Because meningitis and encephalitis can occur suddenly and progress rapidly, anyone suspected of having either condition should immediately contact a doctor or go to the hospital.

Overview

Meningitis and encephalitis are serious health conditions that cause swelling and irritation (inflammation) in and around the brain. Meningitis affects the thin protective coverings (called meninges) around the brain and spinal cord. Encephalitis is inflammation of the brain itself. Both conditions can be life-threatening and need fast medical attention.

Most cases of meningitis in the United States are caused by an infection with a virus, but meningitis can also be caused by infection with bacteria, parasites, or fungi. Some cases improve on their own without treatment, but others need emergency treatment.

Both conditions can affect anyone at any age. People with weakened immune systems are at increased risk for both conditions. This includes people living with HIV or taking medicines that weaken the immune system.

Related Terms: Encephalitis has other names depending on its cause or location in the brain, including:

  • West Nile encephalitis
  • Eastern equine encephalitis
  • Autoimmune encephalitis
  • Limbic encephalitis
  • Herpes simplex encephalitis
  • Rasmussen’s encephalitis
  • NMDA receptor antibody encephalitis
  • Acute disseminated encephalomyelitis
  • Subacute sclerosing panencephalitis

Signs and Symptoms

Meningitis

People with meningitis often develop flu-like symptoms over one to two days. Signs may include:

  • Sudden fever
  • Severe headache
  • Nausea or vomiting
  • Double vision
  • Sensitivity to bright light
  • Stiffness in the neck

Some people with meningitis have unusual rashes. Bacterial meningitis can damage body organs like the kidneys and adrenal glands.

Signs to watch for in infants with meningitis include:

  • Fever
  • Sleepiness or weakness
  • Not waking up for feedings
  • Vomiting
  • Body stiffness
  • Unexplained or unusual irritability
  • The soft spot on a baby’s head (called a fontanel) looks swollen or bigger than normal

Encephalitis

People with encephalitis often have mild flu-like symptoms such as fever, tiredness, headache, or body aches. Other symptoms include:

  • Speech or hearing problems
  • Double vision or vision loss
  • Sudden and/or high fever
  • Seeing things that aren’t there (hallucinations)
  • Personality or behavior changes
  • Loss of consciousness
  • Numbness in some parts of the body
  • Changes in the ability to think
  • Neck stiffness
  • Uncontrollable jerking movements of the head, trunk, or limbs (called myoclonic jerks)
  • Partial paralysis in the arms and legs
  • Trouble thinking clearly about choices
  • Tremors
  • Seizures
  • Memory loss

Signs to watch for in infants with encephalitis include:

  • Fever
  • Sleepiness or weakness
  • Not waking up for feedings
  • Vomiting
  • Body stiffness
  • Unexplained or unusual irritability or crying
  • The soft spot on a baby’s head (called a fontanel) looks swollen or bigger than normal

Both meningitis and encephalitis can cause serious health problems, including:

  • Stroke
  • Hearing and/or speech loss
  • Blindness
  • Permanent brain and nerve damage
  • Behavioral changes
  • Thinking and learning disabilities
  • Loss of muscle control
  • Seizures
  • Memory loss

Causes and Risk Factors

Meningitis

Most cases of meningitis in the United States are caused by an infection with a virus, but meningitis can also be caused by infection with bacteria, parasites, or fungi. Meningitis caused by bacteria is often very serious and should be treated as a medical emergency. Cases of meningitis caused by viruses are usually mild and get better on their own. But they can be serious and require medical care, especially in people with weakened immune systems, infants, or older adults.

Meningitis can be caused by different types of bacteria:

  • Pneumococcal meningitis: This is the most common and serious type of bacterial meningitis. It is particularly dangerous for children under age 2 and adults with a weakened immune system. People who have had it often have neurological damage, which can range from deafness to severe brain damage.
  • Meningococcal meningitis: This type of bacterial meningitis is very contagious. It often affects infants, people with weakened immune systems, people who travel to countries where the disease is common, and people who live in shared housing such as college dormitories or military barracks.
  • Listeria monocytogenes meningitis: This type of bacterial meningitis can come from foods such as unpasteurized dairy or deli meats. It is most common in older adults, infants, and people with weakened immune systems.
  • E. coli meningitis: This type of bacterial meningitis is more common in older adults, infants, and people with implanted brain devices or who have had brain surgery.
  • Mycobacterium tuberculosis meningitis: This type of bacterial meningitis occurs in people who have tuberculosis.
  • Haemophilus influenzae meningitis: This type of bacterial meningitis used to be the most common form of bacterial meningitis. But the HIB (haemophilus influenzae b) vaccine has greatly reduced the number of cases in the United States. Those most at risk are children in child-care settings and children who do not get the vaccine.

Meningitis can be caused by different types of viruses:

Meningitis can be caused by fungi:

  • Cryptococcus neoformans, a fungus found in bird droppings and dirt. This type of meningitis usually affects people with weakened immune systems but can also occur in healthy people.

Meningitis can be caused by different types of parasites:

  • Cysticercosis: This type of meningitis is caused by a brain infection from a tapeworm. Tapeworm eggs are in contaminated food, water, or unwashed hands.
  • Cerebral malaria: This type of meningitis is caused by a severe form of malaria that affects the brain.
  • Rare cases of meningitis are caused by amoebas (tiny living organisms you can’t see that are often found in water and soil).

Not all meningitis is caused by infections. Non-infectious causes of meningitis are caused by certain immune diseases (autoimmune and rheumatological diseases) and some medicines.

Causes of Encephalitis

Encephalitis is inflammation of the brain or spinal cord. It can either be caused by infections with viruses or other microbes, including HIV and other viruses. Encephalitis can also be caused by immune diseases or in people with weakened immune systems who are taking medicines that weaken their immune system.

In the United States, most cases of encephalitis are caused by:

  • Herpes simplex virus types 1 and 2: These are common viruses that cause sores in the mouth or genital areas.
  • Arboviruses (such as West Nile Virus): These are transmitted through the bite of an infected tick, mosquito, or other blood-sucking insect.
  • Enteroviruses: They spread from person to person, especially through germs on hands, surfaces, or in the air.
  • Rabies virus: People can become infected from a bite from an infected animal (like a dog, bat, fox, or raccoon).

Risk Factors for Meningitis and Encephalitis

Some forms of bacterial meningitis and encephalitis are contagious and can spread through contact with:

  • A runny nose
  • Feces
  • Respiratory and throat fluids spread through saliva, like from kissing, coughing, or sharing drinks, eating utensils, or toothbrushes

People sharing a household, at a daycare center, or in a classroom with an infected person can become infected.

Prevention Guidance

Basic hygiene can prevent meningitis. People should wash their hands with soap and avoid sharing food, utensils, glasses, and other objects with someone who may have been exposed to or have it. Shared living areas like college dormitories and military barracks should be cleaned and sanitized regularly.

Effective vaccines are available to prevent certain types of meningitis caused by bacteria. These include Haemophilus influenzae, pneumococcal, and meningococcal meningitis.

Vaccines are also available to prevent certain types of meningitis caused by viruses. These include the viruses that cause measles, mumps, polio, rabies, rubella, and varicella (chickenpox). People traveling to parts of Asia, where tick-borne encephalitis and Japanese encephalitis are found, should get vaccinated before they travel.

People who live, work, or go to school with a person with bacterial meningitis may be prescribed antibiotics for a few days as a preventive measure.

To reduce the risk of being bitten by an infected mosquito or insect:

  • Limit outdoor activities at night.
  • Wear pants and long-sleeved clothing outdoors.
  • Use an EPA-registered insect repellent.
  • Stay away from outdoor areas near standing pools of water where mosquitoes and other insects breed.

Diagnosis

Early diagnosis is very important since symptoms and damage to the body and brain can happen quickly. A doctor or healthcare provider will review a person’s medical history to learn about other health conditions they have and what medicines they are taking. Questions will likely include those about activities over the past several days or weeks. This may include travel, exposure to insects, and contact with sick people. Diagnostic tests may include:

  • A neurological examination to assess motor and sensory function, nerve function, hearing and speech, vision, coordination and balance, mental status, and changes in mood or behavior
  • Lab tests of blood, urine, and body secretions to detect and identify infections and check for conditions with similar symptoms
  • Analysis of spinal fluid obtained through a procedure called a lumbar puncture (sometimes called a spinal tap) to detect infections, inflammation, and other diseases
  • Brain imaging such as a computed tomography (CT) scan or magnetic resonance imaging (MRI) scan can help diagnose meningitis or encephalitis and can also check for other disorders such as stroke and brain tumors
  • EEG (electroencephalography) records brain activity and can show unusual or abnormal patterns

Treatment and Management

People who have meningitis or encephalitis need immediate medical treatment. Each disease can get worse quickly and can cause lasting neurological damage.

Treating Meningitis

Early treatment of bacterial meningitis uses antibiotics that can get into the brain:

  • Anticonvulsant medicines to prevent seizures
  • Oral steroid medicines to reduce brain inflammation, relieve pressure and swelling, and prevent hearing loss

Antibiotics do not work for meningitis caused by viruses. Cases of meningitis caused by viruses are usually mild and get better on their own. But they can be serious and require medical care, especially in people with weakened immune systems, infants, or older adults. Meningitis caused by fungi can be life-threatening and is usually treated with antifungal medicines delivered directly through a vein.

People who have only headaches, fever, and a stiff neck may recover from meningitis in two to four weeks. People with bacterial meningitis typically feel better two or three days after being treated but are more likely to have complications. People with serious cases of meningitis may need long-term treatment and supportive care.

Treating Encephalitis

Treatment for encephalitis depends on what causes it. Treatment can include antiviral medicines, antibiotics, oral steroid medicines, and other medicines. Some severe types of encephalitis cannot be prevented or treated with vaccines or medicines. In these cases, supportive care like rest, nutrition, and fluids can help the body fight the infection and relieve symptoms.

Specific treatments for encephalitis include:

  • Antiviral drugs such as acyclovir and ganciclovir can treat infectious encephalitis caused by a virus
  • Antibiotics can treat infectious encephalitis caused by bacteria
  • Immunosuppressant medicines (and checking for other causes like tumors) can treat autoimmune encephalitis
  • Anticonvulsants can stop or prevent seizures
  • Oral steroid medicines can reduce brain swelling
  • Sedatives may be prescribed if a person is irritable or restless
  • Acetaminophen can relieve fever or headache
  • Artificial respiration may be needed for people with encephalitis having difficulty breathing

People with encephalitis usually improve and begin to recover in one to two weeks. They may need therapy to help with thinking, movement, speech, and daily activities if the brain has been affected.

In most cases, people with very mild encephalitis that does not last long can make a full recovery. But the process may be slow and take several months, and problems with thinking and memory can continue. People with serious cases of encephalitis may need long-term treatment and supportive care.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on meningitis and clinical trials on encephalitis.

Community Support

Note: This resource list is for informational purposes only. It is not comprehensive, and an organization’s inclusion does not constitute an endorsement by NIH.  

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

Meningitis Research

Research has led to vaccines for many types of meningitis. NIH research has contributed to understanding how meningitis infection can permanently damage the brain’s immune system and weaken immune cells in the brain’s outer coating (the meninges), preventing the ability to fight off future infections.

NIH-funded researchers are currently:

  • Exploring ways to help people with cryptococcal meningitis live longer after a diagnosis
  • Studying brain changes in people with both tuberculosis meningitis and stroke
  • Investigating the impact of E. coli in infants, toward identifying diet-based changes to keep the bacteria from taking hold in the body

Current diagnostic tests for some types of meningitis are not very sensitive and may miss positive cases. NIH-funded researchers are also working to identify tests for tuberculosis meningitis, which is a dangerous type of meningitis.

Encephalitis Research

NIH-supported researchers are studying inebilizumab, a promising treatment for NMDA receptor antibody encephalitis—one of the most common causes of autoimmune encephalitis. This research aims to improve recovery, measure health outcomes more effectively, and find better ways to predict how patients will do.

Researchers are also looking at ways to prevent viral infections from spreading from the nose to the brain.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.