What Are the Types of Encephalitis?

Encephalitis—inflammation of the brain—can be primary or secondary. Primary encephalitis occurs when a virus infects the brain, while secondary encephalitis is caused by an infection from a different part of the body that traveled to the brain.

The inflammation causes the brain to swell, which can lead to headache, stiff neck, sensitivity to light, mental confusion, and seizures. This requires immediate medical attention.

There are several types of encephalitis, and they are a result of different types of viruses and other causes.

How Common Is Encephalitis?

Encephalitis affects 10 to 15 people per 100,000 each year, with more than 250,000 patients diagnosed in the last decade alone in the United States. 

woman with headache holding her head

Jamie Grill / Getty Images

Causes and Symptoms

The three most common causes of encephalitis in the United States are:

  • Herpes simplex virus types 1 and 2
  • Arboviruses, which are transmitted from infected blood-sucking insects like ticks or mosquitos
  • Enteroviruses

In extremely rare cases, a Lyme disease bacterial infection or the rabies virus can cause encephalitis.

Being infected does not necessarily mean you will develop encephalitis, though. Symptoms include:

  • Decreased appetite
  • Fatigue
  • Feeling sick
  • Nausea or vomiting
  • Fever
  • Headache
  • Seizures
  • Behavioral changes
  • Confusion 
  • Problems with speech or hearing
  • Stiff neck

Types of Encephalitis 

Epidemic Encephalitis

Enterovirus can enter your gastrointestinal tract or respiratory system and cause an infection. They can travel to the central nervous system. It can then cause the death of neurons and, unique to this type of encephalitis, paralysis.

On the other hand, arborviruses enter your bloodstream when an infected insect (typically a tick or mosquito) bites you. Symptoms of this infection include light sensitivity and extreme weakness.

There have been outbreaks in recent years in the United States of several types of encephalitis, such as West Nile encephalitis and St. Louis encephalitis. Travelers abroad are most at risk for Japanese encephalitis and tick-borne encephalitis.

People can be infected by the bite of infected Ixodes ricinus ticks. This usually happens in those who visit or work in forests, fields, or pastures. You can also get the infection by consuming unpasteurized dairy products from infected cows, goats, or sheep. The risk of getting the disease is greatest from April through August, when ticks are most active.

Sporadic Encephalitis

Herpes simplex type 1 and type 2 are commonly contracted during childhood. It causes sporadic encephalitis, and is most commonly seen in the 20 to 40 age group. Symptoms are very similar to those of other types of encephalitis, but people with this infection can also have altered levels of consciousness.

Rabies is an extremely rare cause of encephalitis in the United States. It is transmitted when rabid animals bite humans. The virus differs from all other viruses causing encephalitis because it goes undetected by the immune system and targets the central nervous system. 

Unique symptoms of encephalitis caused by rabies include:

  • Signs of autonomic dysfunction, including excessive sweating and salivating and pupil dilation 
  • Progressive and debilitating fear of swallowing water
  • Phobic spasms in response to stimuli like fear-stricken jerks in response to noises

Autoimmune Encephalitis

This is a noninfectious type of encephalitis. It can be a result of an autoimmune disorder that has been triggered by an infection.

NMDA-receptor encephalitis (Anti-N-methyl D-aspartate encephalitis) is the most common type of autoimmune encephalitis. It presents in the early stages as a viral illness and then with psychotic symptoms that may be missed or misdiagnosed as schizophrenia symptoms.

Symptoms include:

  • Upper respiratory problems
  • Paranoia
  • Hyper-religiosity 
  • Agitation to point of combativeness


Early diagnosis is important to effective treatment of encephalitis. The diagnostic process will begin with the doctor taking a medical history and performing a physical exam.

Your doctor will then order tests to check for infection, including:

  • Neurological exam: Assesses motor skills and sensory functions
  • Blood, urine, and body secretion screening: Detects antibodies and foreign proteins
  • A spinal tap: Tests for bacteria, blood, viruses, glucose, and white blood cells as well as well protein and antibody levels in cerebrospinal fluid (CSF)
  • Computed tomography (CT) scan: Checks for inflammation in the brain
  • Magnetic resonance imaging (MRI): Checks for brain or spinal cord inflammation, infection, tumors, or other conditions
  • Electroencephalography (EEG): Identifies abnormal brain waves that could indicate viral infection

Treatment and Prevention

Treatment options for encephalitis include:

  • Antiviral medications: These drugs can be used to treat viral encephalitis, such as Zovirax (acyclovir).
  • Immunosuppressants: These can be added to your existing medication regime to treat autoimmune encephalitis.
  • Anticonvulsants: These medications can help with seizure prevention and reduce the frequency of them happening.
  • Corticosteroids: They can be used to reduce brain swelling.
  • Artificial respiration: Respirators can help with breathing difficulties.
  • Comprehensive rehabilitation: This can help treat physical, speech, or occupational dysfunction.

Steps to prevent encephalitis infection can include:

  • Protect yourself from insect bites, especially in areas with known cases, with DEET bug spray
  • Wear light-colored clothing in wooded or grassy areas (tiny bugs are easier to detect on lighter colors) 
  • Practice mosquito control measures by using screen doors and mosquito netting to keep bugs out and spraying repellent or insecticide (permethrin) to keep them away
  • Dry up any pools of water on your lawn or outdoor area
  • Limit your nighttime outdoor activities
  • Avoid unpasteurized milk or dairy products
  • Get vaccinated against some types of encephalitis
  • Maintain proper hand hygiene (frequent washing with soap and water) and do not share utensils, food, and glasses with people who have or may have encephalitis


Encephalitis, regardless of the cause, is a serious condition that requires immediate medical attention. If you have been outside and begin having symptoms of encephalitis, you may have become infected with a virus carried by insects.

A Word From Verywell

While many types of encephalitis are rare, you can never be too careful. If infected, the illness can progress quickly and cause life-threatening symptoms. If you are concerned about symptoms, reach out to your doctor while they are mild. Do not wait for them to resolve on their own (they won’t). Talk to your local clinic or community center about your risk factors and your area’s history of active cases. 

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Johns Hopkins Medicine. Encephalitis.

  3. National Institute of Neurological Disorders and Stroke. Meningitis and encephalitis fact sheet.

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By Michelle Pugle
Michelle Pugle, BA, MA, is an expert health writer with nearly a decade of contributing accurate and accessible health news and information to authority websites and print magazines. Her work focuses on lifestyle management, chronic illness, and mental health. Michelle is the author of Ana, Mia & Me: A Memoir From an Anorexic Teen Mind.