What Is Encephalitis?

Encephalitis is an inflammation of brain tissues associated with swelling, headaches, flu symptoms, and mental confusion. It has a variety of causes, ranging from viral and bacterial infections to cancers and autoimmune diseases. Though rarely fatal, encephalitis is a potentially serious medical condition that requires immediate diagnosis and treatment. Those particularly at risk are the young and the old, especially when living in certain geographic locations and during certain times of the year, when viral infections are common. 

What Are the Symptoms of Encephalitis?

Encephalitis is associated with a wide range of symptoms, including:
  • Headaches and neck stiffness
  • Nausea and loss of appetite
  • Photophobia (light sensitivity)
  • Fatigue, achiness, and other flu-like symptoms
  • Mental fogginess or confusion
  • Unsteadiness in standing and walking
  • Personality change (for example, greater irritability)
  • Feelings of lethargy and sleepiness
Symptoms of an advanced case include:
  • Hallucinations
  • Double vision
  • Impaired hearing and speech
  • Partial paralysis of the limbs
  • Coma

What Causes Encephalitis?

The causes of encephalitis can’t always be determined with certainty but the most common trigger is viral infection. There are several viruses associated with the development of this illness:
  • Herpes viruses: Included in this group are Herpes Simplex Viruses 1 and 2 (oral and genital herpes), as well as the varicella-zoster virus (shingles and chickenpox) and the Epstein-Barr virus (mononucleosis).
  • Tick-borne viruses: Ticks in the Midwestern U.S. carry the Powassan virus, which has been linked to encephalitis. 
  • Mosquito-borne viruses: Mosquitos carry the West Nile and other viruses, which are associated with several types of encephalitis, including West Nile, La Crosse, St. Louis, and both the eastern and western equine variants. 
  • Rabies: The rabies virus is an occasional cause of encephalitis in the U.S.
  • Enteroviruses: Included here are the poliovirus (polio) and coxsackievirus (aseptic meningitis and other illnesses). 
There are also secondary causes of encephalitis, most commonly autoimmune dysfunction resulting from cancers and other infections. When this occurs, the immune system mistakenly attacks the brain as one source of the infection. Also included in secondary causes are childhood diseases such as mumps and measles, the impact of which has been reduced by widespread vaccination programs.
Risk factors for developing encephalitis are a person’s age, the presence of a compromised immune system, and exposure to insect-borne viruses, depending on where you live, the season of the year, and how much time you spend in certain environments (ticks and mosquitos love the great outdoors).

How Is Encephalitis Diagnosed? 

Your physician will conduct a physical exam and one or more medical tests to diagnose whether you have contracted encephalitis:
  • Medical history and physical exam: In addition to recording your symptoms, your physician will ask questions about your possible contact with disease-causing agents (e.g., Have you recently had a viral infection? Were you bitten by a tick or a mosquito?). 
  • Magnetic resonance imaging (MRI) and CT scans: Imaging scans of the brain can reveal physiological change, such as swelling. 
  • Spinal tap: Alteration of spinal fluid sometimes offers evidence for the presence of a neurological disorder.  
  • Blood, urine, and stool tests: These tests can show signs of infection or immune-system disorder.  
  • Sputum culture: Sputum is a mucous-saliva mix coughed up from the lungs. If infection is present, it will often be evident in sputum.
  • Electroencephalogram (EEG): EEGs record the brain’s electrical activity by means of electrodes attached to the head. Anomalous readings may indicate neurological change or dysfunction.
Two other tests can point to the presence of encephalitis. Intracranial pressure monitoring, or ICP, measures pressure inside the skull. A brain biopsy, which requires a small tissue sample, can also provide evidence of physiological change due to inflammation and swelling. 

How Is Encephalitis Treated? 

Mild cases of encephalitis are treated at home with fluids, rest, and over-the-counter anti-inflammatory medications such as ibuprofen, acetaminophen, and naproxen sodium. Serious cases require more intensive intervention:

Antiviral Care

Because of the role of viruses in causing encephalitis, antiviral medications are often prescribed. Included in this group are acyclovir, foscarnet, and ganciclovir. These have few side effects, though they are not effective in every situation.

Supportive Care

Some persons with encephalitis require a period of hospitalization. They will typically receive intravenous fluids, breathing treatments, anti-inflammatory medications, including corticosteroids, and anticonvulsant drugs, such as phenytoin.


Encephalitis can lead to a certain degree of disability. Physical, occupational, and speech therapy may be required to recover full physical health. Psychotherapy is sometimes indicated to combat mood swings, irritability, or depression.
Many patients recover fully from encephalitis. In more extreme cases, however, long-term brain damage or even death can result.

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