Encephalitis (en-sef-uh-LIE-tis) is inflammation of the brain. It can be caused by viral or bacterial infections, or by immune cells mistakenly attacking the brain. Viruses that can lead to encephalitis can be spread by insects such as mosquitos and ticks.

When inflammation is caused by an infection in the brain, it's known as infectious encephalitis. And when it's caused by the immune system attacking the brain, it's known as autoimmune encephalitis. Sometimes there is no known cause.

Encephalitis can sometimes lead to death. Getting diagnosed and treated right away is important because it's hard to predict how encephalitis may affect each person.

Anyone can develop encephalitis. Factors that may increase the risk include:

• Age. Some types of encephalitis are more common or more serious in certain age groups. In general, young children and older adults are at greater risk of most types of viral encephalitis. Similarly, some forms of autoimmune encephalitis are more common in children and young adults, whereas others are more common in older adults.
• Weakened immune system. People who have HIV/AIDS, take immune-suppressing medicines or have another condition causing a weakened immune system are at increased risk of encephalitis.
• Geographical regions. Mosquito- or tick-borne viruses are common in particular geographical regions.
• Season of the year. Mosquito- and tick-borne diseases tend to be more common in summer in many areas of the United States.
• Autoimmune disease. People who already have an autoimmune condition may be more prone to develop autoimmune encephalitis.
• Smoking. Smoking increases the chances of developing lung cancer, which in turn increases the risk of developing paraneoplastic syndromes including encephalitis.

The complications of encephalitis vary, depending on factors such as:

• Your age.
• The cause of your infection.
• The severity of your initial illness.
• The time from disease onset to treatment.

People with relatively mild illness usually recover within a few weeks with no long-term complications.

Complications of serious illness

Inflammation can injure the brain, possibly resulting in a coma or death.

Other complications may last for months or may be permanent. Complications can vary widely and can include:

• Fatigue that doesn't go away.
• Weakness or lack of muscle coordination.
• Personality changes.
• Memory problems.
• Hearing or vision changes.
• Trouble with speech.

The best way to prevent viral encephalitis is to take precautions to avoid exposure to viruses that can cause the disease. Try to:

• Practice good hygiene. Wash hands often and thoroughly with soap and water, especially after using the toilet and before and after meals.
• Don't share utensils. Don't share tableware and drinks.
• Teach your children good habits. Make sure they practice good hygiene and avoid sharing utensils at home and school.
• Get vaccinations. Keep your own and your children's vaccinations current. Before traveling, talk to your healthcare professional about recommended vaccinations for different destinations.

Protection against mosquitoes and ticks

To minimize your exposure to mosquitoes and ticks:

• Dress to protect yourself. Wear long-sleeved shirts and long pants outside. This is especially important if you're outside between dusk and dawn when mosquitoes are most active. It's also important when you're in a wooded area with tall grasses and shrubs where ticks are more common.
• Apply mosquito repellent. Chemicals such as DEET can be applied to both the skin and clothes. To apply repellent to your face, spray it on your hands and then wipe it on your face. If you're using both sunscreen and a repellent, apply sunscreen first.
• Use insecticide. The Environmental Protection Agency recommends the use of products containing permethrin, which repels and kills ticks and mosquitoes. These products can be sprayed on clothing, tents and other outdoor gear. Permethrin shouldn't be applied to the skin.
• Avoid mosquitoes. Stay away from places where mosquitoes are most common. If possible, don't do outdoor activities from dusk till dawn when mosquitoes are most active. Repair broken windows and screens.
• Get rid of water sources outside your home. Eliminate standing water in your yard, where mosquitoes can lay their eggs. Common places include flowerpots or other gardening containers, flat roofs, old tires, and clogged gutters.
• Look for outdoor signs of viral disease. If you notice sick or dying birds or animals, report your observations to your local health department.

Protection for young children

Insect repellents aren't recommended for use on infants younger than 2 months of age. Instead, cover an infant carrier or stroller with mosquito netting.

For older infants and children, repellents with 10% to 30% DEET are considered safe. Products containing both DEET and sunscreen aren't recommended for children. This is because reapplying for sunscreen protection can expose the child to too much DEET.

Tips for using mosquito repellent with children include:

• Always assist children with the use of mosquito repellent.
• Spray on clothing and exposed skin.
• Apply the repellent when outdoors to lessen the risk of inhaling the repellent.
• Spray repellent on your hands and then apply it to your child's face. Take care around the eyes and ears.
• Don't use repellent on the hands of young children who may put their hands in their mouths.
• Wash treated skin with soap and water when you come indoors.

To diagnose encephalitis, a member of your healthcare team does a physical exam and takes your medical history.

Your healthcare professional might then recommend:

• Brain imaging. MRI or CT images can reveal any swelling of the brain or another condition that might be causing your symptoms, such as a tumor.
• Spinal tap, known as a lumbar puncture. A needle inserted into your lower back removes a small amount of cerebrospinal fluid (CSF), the protective fluid that surrounds the brain and spinal column. Changes in this fluid can point to infection and inflammation in the brain. Sometimes samples of CSF can be tested to identify the cause. This may include testing for infection or the presence of antibodies associated with autoimmune encephalitis.
• Other lab tests. Samples of blood, urine or excretions from the back of the throat can be tested for viruses or other infectious agents.
• Electroencephalogram (EEG). Electrodes attached to your scalp record the brain's electrical activity. Certain patterns may point to encephalitis.
• Body imaging. Sometimes, autoimmune encephalitis may be triggered by an immune response to a tumor in the body. The tumor may be noncancerous or cancerous. Your healthcare professional may order imaging studies, such as ultrasound, MRI, CT or PET-CT scans. These scans may look at your chest, stomach area or pelvis to check for these tumors. If a mass is found, a small piece of it may be removed to study it in a lab. This is known as a biopsy.
• Brain biopsy. Rarely, a small sample of brain tissue might be removed for testing. A brain biopsy is usually done only if symptoms are worsening and treatments are having no effect.

Treatment for mild encephalitis usually consists of:

• Bed rest.
• Plenty of fluids.
• Anti-inflammatory medicines — such as acetaminophen (Tylenol, others), ibuprofen (Advil, Motrin IB, others) and naproxen sodium (Aleve) — to relieve headaches and fevers.

Antiviral medicines

Encephalitis caused by certain viruses usually requires antiviral treatment.

Antiviral medicines commonly used to treat encephalitis include:

• Acyclovir (Zovirax, Sitavig).
• Ganciclovir.
• Foscarnet (Foscavir).

Some viruses, such as insect-borne viruses, don't respond to these treatments. But because the specific virus may not be identified right away or at all, you may be treated with acyclovir. Acyclovir can be effective against HSV, which can result in serious complications when not treated quickly.

Antiviral medicines are generally well tolerated. Rarely, side effects can include kidney damage.

Autoimmune encephalitis

If the tests show an autoimmune cause of encephalitis, then medicines that target your immune system, known as immunomodulatory medicines, or other treatments may be started. These may include:

• Intravenous or oral corticosteroids.
• Intravenous immunoglobulin.
• Plasma exchange.

Some people with autoimmune encephalitis need long-term treatment with immunosuppressive medicines. These may include azathioprine (Imuran, Azasan), mycophenolate mofetil (CellCept), rituximab (Rituxan) or tocilizumab (Actemra).

Autoimmune encephalitis caused by tumors may require treatment of those tumors. This may include surgery, radiation, chemotherapy or a combination of treatments.

Supportive care

People who are hospitalized with serious encephalitis might need:

• Breathing assistance, as well as careful monitoring of breathing and heart function.
• Intravenous fluids to ensure proper hydration and levels of essential minerals.
• Anti-inflammatory medicines, such as corticosteroids, to reduce swelling and pressure within the skull.
• Anti-seizure medicines to stop or prevent seizures.

Follow-up therapy

If you experience complications of encephalitis, you might need additional therapy, such as:

• Brain rehabilitation to improve cognition and memory.
• Physical therapy to improve strength, flexibility, balance, motor coordination and mobility.
• Occupational therapy to develop everyday skills and to use adaptive products that help with everyday activities.
• Speech therapy to relearn muscle control and coordination to produce speech.
• Psychotherapy to learn coping strategies and new behavioral skills to improve mood disorders or address personality changes.

Serious illness associated with encephalitis is usually severe and relatively sudden, so seek emergency medical care. Your healthcare team will likely include specialists in infectious diseases and in the brain and nervous system, known as neurologists.

Questions from your doctor

You may need to answer these questions, or answer them on behalf of your child or another person with a serious illness:

• When did the symptoms begin?
• Have you recently started taking any new medicines? If so, what is the medicine?
• Have you been bitten by a mosquito or tick during the past few weeks?
• Have you traveled recently? Where?
• Have you recently had a cold, flu or other illness?
• Are you up to date on your immunizations? When was your last one?
• Have you had any exposure to wild animals or known toxins recently?
• Have you had unprotected sex with a new or long-term sexual partner?
• Do you have a condition or take any medicines that result in a weakened immune system?
• Do you have an autoimmune condition or do autoimmune conditions run in the family?