Condition 101 About Encephalitis

What is the definition of Encephalitis?

Encephalitis is irritation and swelling (inflammation) of the brain, most often due to infections.

What are the causes for Encephalitis?

Encephalitis is a rare condition. It occurs more often in the first year of life and decreases with age. The very young and older adults are more likely to have a severe case.

Encephalitis is most often caused by a virus. Many types of viruses may cause it. Exposure can occur through:

  • Breathing in droplets from the nose, mouth, or throat from an infected person
  • Contaminated food or drink
  • Mosquito, tick, and other insect bites
  • Skin contact

Different viruses occur in different locations. Many cases occur during a certain season.

Encephalitis caused by the herpes simplex virus is the leading cause of more severe cases in all ages, including newborns.

Routine vaccination has greatly reduced encephalitis due to some viruses, including:

  • Measles
  • Mumps
  • Polio
  • Rabies
  • Rubella
  • Varicella (chickenpox)

Other viruses that cause encephalitis include:

  • Adenovirus
  • Coxsackievirus
  • Cytomegalovirus
  • Eastern equine encephalitis virus
  • Echovirus
  • Japanese encephalitis, which occurs in Asia
  • West Nile virus

After the virus enters the body, the brain tissue swells. This swelling may destroy nerve cells, and cause bleeding in the brain and brain damage.

Other causes of encephalitis may include:

  • An allergic reaction to vaccinations
  • Autoimmune disease
  • Bacteria such as Lyme disease, syphilis, and tuberculosis
  • Parasites such as roundworms, cysticercosis, and toxoplasmosis in people with HIV/AIDS and other people who have a weakened immune system
  • The effects of cancer

What are the symptoms for Encephalitis?

Some people may have symptoms of a cold or stomach infection before encephalitis symptoms begin.

When this infection is not very severe, the symptoms may be similar to those of other illnesses:

  • Fever that is not very high
  • Mild headache
  • Low energy and a poor appetite

Other symptoms include:

  • Clumsiness, unsteady gait
  • Confusion, disorientation
  • Drowsiness
  • Irritability or poor temper control
  • Light sensitivity
  • Stiff neck and back (sometimes)
  • Vomiting

Symptoms in newborns and younger infants may not be as easy to recognize:

  • Body stiffness
  • Irritability and crying more often (these symptoms may get worse when the baby is picked up)
  • Poor feeding
  • Soft spot on the top of the head may bulge out more
  • Vomiting

Emergency symptoms:

  • Loss of consciousness, poor responsiveness, stupor, coma
  • Muscle weakness or paralysis
  • Seizures
  • Severe headache
  • Sudden change in mental functions, such as flat mood, impaired judgment, memory loss, or a lack of interest in daily activities

What are the current treatments for Encephalitis?

The goals of treatment are to provide supportive care (rest, nutrition, fluids) to help the body fight the infection, and to relieve symptoms.

Medicines may include:

  • Antiviral medicines, if a virus caused the infection
  • Antibiotics, if bacteria is the cause
  • Antiseizure medicines to prevent seizures
  • Steroids to reduce brain swelling
  • Sedatives for irritability or restlessness
  • Acetaminophen for fever and headache

If brain function is severely affected, physical therapy and speech therapy may be needed after the infection is controlled.

What is the outlook (prognosis) for Encephalitis?

The outcome varies. Some cases are mild and short, and the person fully recovers. Other cases are severe, and permanent problems or death is possible.

The acute phase normally lasts for 1 to 2 weeks. Fever and symptoms gradually or suddenly disappear. Some people may take several months to fully recover.

What are the possible complications for Encephalitis?

Permanent brain damage may occur in severe cases of encephalitis. It can affect:

  • Hearing
  • Memory
  • Muscle control
  • Sensation
  • Speech
  • Vision

When should I contact a medical professional for Encephalitis?

Go to the emergency room or call the local emergency number (such as 911) if you have:

  • Sudden fever
  • Other symptoms of encephalitis

How do I prevent Encephalitis?

Children and adults should avoid contact with anyone who has encephalitis.

Controlling mosquitoes (a mosquito bite can transmit some viruses) may reduce the chance of some infections that can lead to encephalitis.

  • Apply an insect repellant containing the chemical, DEET when you go outside (but DO NOT use DEET products on infants younger than 2 months).
  • Remove any sources of standing water (such as old tires, cans, gutters, and wading pools).
  • Wear long-sleeved shirts and pants when outside, especially at dusk.

Children and adults should get routine vaccinations for viruses that can cause encephalitis. People should receive specific vaccines if they are traveling to places such as parts of Asia, where Japanese encephalitis is found.

Vaccinate animals to prevent encephalitis caused by the rabies virus.


Bloch KC, Glaser CA, Tunkel AR. Encephalitis and myelitis. In: Cohen J, Powderly WG, Opal SM, eds. Infectious Diseases. 4th ed. Philadelphia, PA: Elsevier; 2017:chap 20.

Bronstein DE, Glaser CA. Encephalitis and meningoencephalitis. In: Cherry JD, Harrison GJ, Kaplan SL, Steinbach WJ, Hotez PJ, eds. Feigin and Cherry's Textbook of Pediatric Infectious Diseases. 8th ed. Philadelphia, PA: Elsevier; 2019:chap 36.

Lissauer T, Carroll W. Infection and immunity. In: Lissauer T, Carroll W, eds. Illustrated Textbook of Paediatrics. 5th ed. Philadelphia, PA: Elsevier; 2018:chap 15.

Latest Advances On Encephalitis

  • Condition: Subsegmental Pulmonary Embolism (SSPE) in Patients with Cancer
  • Journal: Blood advances
  • Treatment Used: Anticoagulation Therapy
  • Number of Patients: 206
  • Published —
This study identified the incidence and risk factors of recurrent proximal pulmonary embolism (clot) within 1 subsegmental pulmonary embolism (SSPE) in patients with cancer.
  • Condition: Herpes Simplex Virus Type 1-Related Acute Retinal Necrosis following Encephalitis Illness
  • Journal: BMC neurology
  • Treatment Used: Retinal Detachment Surgery
  • Number of Patients: 1
  • Published —
This case report describes a patient that acquired acute retinal necrosis due to encephalitis from herpes simplex virus type 1.

Clinical Trials For Encephalitis

Clinical Trial
  • Status: Not yet recruiting
  • Phase: Phase 1
  • Intervention Type: Drug
  • Participants: 120
  • Start Date: December 30, 2021
Tracking Peripheral Immune Cell Infiltration of the Brain in Central Inflammatory Disorders Using [Zr-89]Oxinate-4-labeled Leukocytes.
Clinical Trial
  • Status: Not yet recruiting
  • Intervention Type: Diagnostic Test
  • Participants: 715
  • Start Date: March 1, 2021
Establishment of Prevention and Control System of Central Nervous System Infection