Encephalitis Fast Facts

Up to 60% of all cases of encephalitis go undiagnosed.

The CDC documents several thousand encephalitis cases in the United States each year but estimates that many more cases go unreported because symptoms are mild or non-existent.

Approximately 175 cases of herpes simplex encephalitis (HSE) occur each year in the United States, accounting for about 10% of all encephalitis cases. When left untreated, the fatality rate of HSE is greater than 50%.

HSE is most common in adults between the ages of 20 and 40.

Eastern equine encephalitis usually affects fewer than ten people in the United States each year, but the disease’s fatality rate can be as high as 30%.

United Brain Association

The most common cause of encephalitis is an infection by one of several types of viruses, some of which are spread by the bite of infected insects or ticks.

What is Encephalitis?

Encephalitis is inflammation and swelling of brain tissue. Although the symptoms in most cases are mild, the condition can cause significant impairment of brain function.

The most common cause of encephalitis is an infection by one of several types of viruses, some of which are spread by the bite of infected insects or ticks. Bacterial infections and inflammatory conditions can also sometimes cause encephalitis, and one type of the disease is caused by an abnormal reaction of the body’s immune system.

In many cases, encephalitis produces no symptoms at all, and in mild cases, the symptoms often resemble those of the flu, including fever, body aches, fatigue, and headache.

Other common encephalitis symptoms include:

  • Stiff neck
  • Light sensitivity
  • Irritability, moodiness, or personality changes
  • Fatigue, lethargy, or sleepiness
  • Loss of appetite
  • Balance problems
  • Nausea or vomiting
  • Seizures

In more severe cases, symptoms can include weakness or paralysis of limbs and problems with speech, vision, or hearing.

What Causes Encephalitis?

Encephalitis is often a result of a viral infection that directly affects the brain, causing inflammation and swelling. These types of the disease are called primary encephalitis. They are often transmitted to humans by the bite of a tick, insect, or another animal infected with the virus.

Types of viral encephalitis include:

  • Herpes simplex encephalitis (HSE) is caused by the herpes simplex virus types 1 and 2. The brain inflammation may result from the reactivation of a virus that was already present and inactive in the body. Herpes simplex virus type 1 causes cold sores and is commonly acquired in childhood. The type 2 virus is usually spread through sexual contact. HSE is rare but is potentially very serious or even fatal.
  • Mosquito-born viral encephalitis types include Eastern equine encephalitis, Western equine encephalitis, West Nile encephalitis, La Crosse encephalitis, and St. Louis encephalitis. These types usually cause flu-like symptoms within days or weeks after the mosquito bite.
  • Tick-borne viral encephalitis includes Powassan encephalitis, which produces symptoms within 7-10 days after the bite of an infected tick.
  • Rabies virus is transmitted through a bite or scratch from an infected animal, and symptoms rapidly progress to severe encephalitis. Cases of rabies are rare in the United States, but the disease is almost always fatal if left untreated.
  • Bacterial or protozoan infections such as toxoplasmosis or malaria may also be a cause.

Sometimes encephalitis is caused by the body’s immune system as it tries to fight off another infection. In this case, the immune system mistakes proteins in nerve cells with those in a virus, causing the immune system to attack the healthy nerve cells. This type of encephalitis is called secondary encephalitis, post-infection encephalitis, or autoimmune encephalitis.

Infections that may trigger autoimmune encephalitis include:

  • Enterovirus infections
  • Epstein-Barr virus
  • Hepatitis A or B
  • Influenza
  • Human immunodeficiency virus (HIV)
  • Childhood diseases such as measles, mumps, and rubella
  • Cancer

Another form of autoimmune encephalitis occurs when the immune system attacks nerve-cell proteins called N-methyl-d-aspartate (NMDA) receptors. Called anti-NMDA receptor encephalitis, this type of the disease sometimes follows cases of herpes simplex encephalitis.

Is Encephalitis Hereditary?

In general, there seems to be little connection between family health history and the development of encephalitis. One study, however, has suggested that susceptibility to one type of encephalitis might come from a deficiency in a particular gene, and that deficiency might be inherited within families.

In 2006, researchers in France found that some otherwise healthy patients could not produce a protein that helps the immune system recognize viruses and other pathogens. The lack of this protein made the patients’ cells vulnerable to herpes simplex type 1 infections.

The researchers suggested that this vulnerability could lead to an increased risk of developing herpes simplex encephalitis. Further, they indicated that the gene mutation that causes the protein deficiency could be inherited rather than being driven by external environmental factors.

How Is Encephalitis Detected?

Early detection, diagnosis, and treatment of encephalitis are essential. Although many cases are relatively mild and may resolve on their own, severe cases of encephalitis–and especially types like herpes simplex encephalitis and eastern equine encephalitis–are likely to cause long-term harm or even death if left untreated and allowed to progress.

Early signs of encephalitis, which often precede the more commonly recognized symptoms, include:

  • Nausea or vomiting
  • Abdominal pain
  • Diarrhea
  • Cough
  • Sore throat
  • Runny nose
  • Body aches
  • Fever
  • Swollen lymph nodes

As encephalitis progresses, other more profound symptoms usually emerge, such as:

  • Headache
  • Confusion or disorientation
  • Irritability or mood changes
  • Numbness or paralysis in limbs
  • Seizures
  • Unusual sleepiness or fatigue

You should see a doctor immediately if you experience severe symptoms such as high fever, intense headache, or pronounced confusion. Children who exhibit any symptoms should also see a doctor immediately.

How Is Encephalitis Diagnosed?

If you exhibit symptoms consistent with encephalitis, your healthcare provider will move through a series of diagnostic steps to see if you have the condition.

  • Physical exam and medical history. The doctor will look for signs that you may be at risk for encephalitis. He or she may ask if you’ve recently had a gastrointestinal or respiratory illness (cold or flu), if you’ve been at risk for a tick or mosquito bite, or if you’ve recently traveled to areas where encephalitis is known to be prevalent.
  • Laboratory tests. Tests of your blood, urine, stool, and throat cultures can determine whether or not there is an infection in your body that could lead to encephalitis.
  • Electroencephalogram (EEG). This test monitors your brain’s electrical activity and can help to detect abnormalities in brain function.
  • Imaging tests. Magnetic resonance imaging (MRI) and computed tomography (CT) scans can detect brain swelling caused by encephalitis. These tests may also rule out encephalitis by revealing another condition that’s causing your symptoms.
  • Spinal tap. This procedure removes and tests a small amount of the fluid that protects your brain and spinal column. The test can often detect viral infections or inflammation in the brain.
  • Brain biopsy. This test, in which a small amount of brain tissue is removed and tested, is rarely used to diagnose encephalitis, but it may be necessary if the condition does not respond to initial treatment.

How Is Encephalitis Treated?

Treatment for encephalitis involves both controlling the inflammation and swelling of the brain, which can cause long-term damage and death, and treating the underlying infection or immune system problem that caused the encephalitis in the first place.

Treatment for mild cases of encephalitis typically includes:

  • Bed rest
  • Sufficient hydration
  • Over-the-counter anti-inflammatory medications such as acetaminophen, ibuprofen, or naproxen sodium

When encephalitis symptoms are severe and require hospitalization, more advanced treatments can include:

  • Intravenous hydration
  • Mechanical breathing assistance
  • More aggressive anti-inflammatory medications such as corticosteroids
  • Anticonvulsant drugs to treat seizures

The infections that cause viral encephalitis can be treated with anti-viral drugs such as:

  • Acyclovir to treat the herpes simplex or chickenpox (varicella-zoster) virus
  • Ganciclovir or foscarnet to treat cytomegalovirus
  • Antiretroviral medications to treat HIV-related encephalitis

Bacterial infections may be treated with antibiotics.

Autoimmune encephalitis is often treated with corticosteroids such as prednisone or methylprednisolone. Other approaches include transfusions of blood plasma to remove abnormal antibodies or the intravenous administration of normal antibodies.

How Does Encephalitis Progress?

Encephalitis may become a severe health threat depending on its cause, the severity of the initial infection, and the length of time that the condition goes untreated. Especially young or elderly patients are at the most significant risk of developing life-threatening complications.

With treatment, mild cases usually resolve within a few weeks and don’t cause long-term or permanent complications. Severe cases, however, may produce permanent complications, and the worst cases can result in coma or death.

Long-term or permanent complications may include:

  • Concentration or mental focus difficulties
  • Memory loss
  • Fatigue or weakness
  • Irritability or personality changes
  • Seizures
  • Paralysis
  • Problems with speech, hearing, or vision

How Is Encephalitis Prevented?

The best prevention strategy for encephalitis is avoiding the infections that may cause the condition.

To protect yourself from the common viruses that cause encephalitis, take these steps:

  • Vaccinate yourself and your children against common viruses such as measles, mumps, rubella, and chickenpox. If you’re traveling to foreign destinations, ask your doctor if you need vaccinations against locally prevalent viruses, bacteria, or protozoa.
  • Wash your hands and practice good hygiene to prevent the spread of viruses. Teach your children these practices, too.
  • Don’t share utensils, food, or beverages.

To guard against tick- or mosquito-borne encephalitis, these precautions are recommended:

  • Wear long sleeves and long pants when you’re outside, especially in areas of tall grass and between dusk and dawn.
  • Use insect repellents and insecticides.
  • Avoid wet areas where mosquitoes are common and don’t allow standing water to collect around your home.

Encephalitis Caregiver Tips

After surviving a severe case of encephalitis, patients are often forced to deal with complications that may last for years. Although the disease is gone, its lingering effects can make everyday difficult, and caregivers can help sufferers to return to their daily routines as much as possible.

  • Learn as much as you can about the disease and its long-term effects. The sufferer may need help with ongoing therapies, such as physical therapy, occupational therapy, speech therapy, or psychotherapy.
  • Understand that although your loved one may look as if everything is fine, they may be struggling with subtle, unseen complications. Depression and anxiety often result from these struggles, and daily tasks such as paying bills may be difficult, leading to financial missteps. As a caregiver, be aware that these seemingly unrelated problems result from the disease, and be alert for warning signs.
  • Create an environment free of distraction and confusion to help the sufferer cope with any problems with concentration or focus.
  • Find a support group for both the sufferer and yourself as a caregiver. It always helps to know that you’re not alone in what you’re going through.

Many people with anti-NMDA receptor encephalitis also suffer from other brain-related issues, a condition called co-morbidity. Here are a few of the disorders commonly associated with anti-NMDA receptor encephalitis:

  • Many people with anti-NMDA receptor encephalitis experience amnesia.
  • Some people with anti-NMDA receptor encephalitis have problems with excessive sleepiness (hypersomnia) or trouble falling asleep (insomnia).
  • Psychotic symptoms resembling schizophrenia are sometimes associated with anti-NMDA receptor encephalitis.
  • People with anti-NMDA receptor encephalitis may suffer from anxiety.

Encephalitis Brain Science

Encephalitis research includes studies aimed at finding ways to prevent or cure the infections that cause the condition, effective ways to treat the condition when it occurs, and ways to better help patients recover from the effects of encephalitis long term.

One current study is examining the early symptoms of anti-NMDA receptor encephalitis, specifically psychiatric and speech symptoms that occur in the early phases of the condition. These early symptoms often progress to more severe symptoms such as seizures and movement abnormalities. The study hopes to help practitioners better recognize the very early signs so that treatment can begin before the condition becomes more severe.

Another study is looking at the recovery obstacles faced by survivors of autoimmune encephalitis and their caregivers. Researchers hope that by having a more thorough understanding of what it means to live with the effects of encephalitis, practitioners will develop more effective therapies and support systems.

Encephalitis Research

Title: Safety and Immunogenicity Study of the Western Equine Encephalitis (WEE) Vaccine

Stage: Recruiting 

Principal Investigator: Anthony Cardile, DO   

U.S. Army Medical Research and Development Command

Fort Detrick, MD

This study is being conducted to collect safety and immunogenicity data for the WEE vaccine, TSI-GSD 210. Enrollment in this protocol is offered for personnel who enter areas where this virus is used in research or is endemic (an area where this disease process occurs frequently).


Title: Autologous Peripheral Blood Stem Cell Transplant for Neurologic Autoimmune Diseases

Stage: Recruiting 

Contact: George E. Georges

Fred Hutch/University of Washington Cancer Consortium

Seattle, WA

This phase II trial studies the side effects and how well carmustine, etoposide, cytarabine, and melphalan together with antithymocyte globulin before a peripheral blood stem cell transplant works in treating patients with autoimmune neurologic disease that did not respond to previous therapy. In autoimmune neurological diseases, the patient’s own immune system ‘attacks’ the nervous system, including the brain/spinal cord and/or the peripheral nerves. Giving high-dose chemotherapy, including carmustine, etoposide, cytarabine, melphalan, and antithymocyte globulin, before a peripheral blood stem cell transplant weakens the immune system and may help stop the immune system from ‘attacking’ a patient’s nervous system. When the patient’s own (autologous) stem cells are infused into the patient, they help the bone marrow make red blood cells, white blood cells, and platelets so the blood counts can improve.

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