Definition and Overview

Encephalitis is an acute inflammation of the brain commonly caused by a viral infection. It can also occur due to bacterial infections, noninfectious inflammatory conditions, or an abnormal immune response in which the immune system mistakenly attacks brain tissue. Although the condition requires urgent care, it is rarely life threatening.

There are two types of encephalitis - primary and secondary. It is primary if the offending virus or bacterium directly affects the brain and spinal cord. This type may occur sporadically or in many people in the same area at the same time (epidemic). On the other hand, the condition is referred to as post-infectious or secondary encephalitis if the pathogen attacks other parts of the body first before travelling to the brain. Infections that may trigger secondary encephalitis include measles, influenza, mumps, chickenpox, and rubella.

Encephalitis is different from meningitis, which refers to the inflammation of the membranes (meninges) covering the brain. However, the two conditions can co-exist and if they do, it can make diagnosis and treatment more complex.

On its own, viral encephalitis is often treated successfully with medications especially when its diagnosed and treated early. However, the prognosis is not as good for the elderly and very young patients and those whose immune system is compromised.

Causes of Condition

Encephalitis can be caused by viruses and bacteria including those that are transmitted by mosquitoes and other arthropods. Depending on what is causing the infection, the condition can develop abruptly or slowly and its symptoms can range from mild to life threatening.

Encephalitis causes and types

  • Arbovirus - This refers to viruses transmitted by insects and ticks. Worldwide, there are different types of arboviral encephalitis that are transmitted through mosquitoes. These include western equine, eastern equine, St. Louis, and LaCross encephalitis. Arboviral encephalitis is often mild and many patients are either asymptomatic or show very mild symptoms. It is uncommon for the condition to develop into full-blown encephalitis but when it does, it can be quite serious and is often associated with permanent neurological damage.

  • Herpes simplex encephalitis (HSE) - Herpes simplex can sometimes cause encephalitis in some people. It is considered the most serious type because it can lead to significant neurological dysfunction. It commonly affects the elderly and very young children.

  • Rabies - In some underdeveloped and developing countries, encephalitis cases can be caused by rabies, a virus transmitted by certain animals including dogs, raccoons, and foxes. If a person does not receive immediate treatment, the condition can lead to severe encephalitis, which can result in death.

Key Symptoms

Mild cases of encephalitis usually cause fever, headache, joint and muscle pain, and general feeling of weakness or fatigue. Some patients also experience sore throat, muscle stiffness, nausea, upper respiratory tract infection, confusion, and lethargy.

In severe cases, patients may suffer from:

  • Convulsions

  • Disorientation

  • Personality changes

  • Double vision

  • Crossed eyes

  • Increased intracranial pressure

  • Motor dysfunction

  • Partial paralysis of extremities

  • Seizures or loss of consciousness

  • Problems with hearing or speech

In infants and young children, the following can also be observed:

  • Fontanels (soft spots on the skull)

  • Vomiting

  • Nausea

  • Irritability

  • Poor feeding

Who to See and Types of Treatments Available

A person with symptoms mentioned above should immediately seek medical attention. The earlier encephalitis is diagnosed, the better are the treatment outcomes. Depending on the underlying cause, a person with encephalitis can be managed by a general or primary care physician, paediatrician, infectious disease specialist, emergency medicine or critical care specialist, or neurologist.

To diagnose encephalitis, the doctor will review the patient’s medical history and carry out a thorough physical exam. The patient is also commonly asked about his or her travel history in an attempt to identify the cause of the disease. Depending on the results of these tests, doctors may also order the following:

  • Blood and urine tests

  • Computed tomography (CT) scan or magnetic resonance imaging (MRI) of the brain - These imaging tests produce detailed pictures of the brain structures and show any abnormality.

  • Electroencephalogram (EEG) - Used to detect any irregularities in the brain’s electrical activity.

  • Enzyme-linked immunosorbent assays (ELISA) - IgG ELISA and IgM-capture ELISA (MAC-ELISA) can identify which virus has caused encephalitis soon after infection. Polymerase chain reaction (PCR), on the other hand, can be used to identify viral DNA.

  • Spinal tap - Also referred to as lumbar puncture, this procedure involves collecting a small amount of fluid (cerebrospinal fluid) that surrounds the brain and spinal column. The sample taken is then tested in a laboratory for infectious agents.

Encephalitis treatment

Patients with mild encephalitis are often prescribed with anti-inflammatory and antiviral drugs (if the disease is caused by a viral infection). Patients who are otherwise healthy often experience an uneventful recovery within one to two weeks.

Currently, there is no cure for serious arboviral encephalitis. Available treatment methods focus on relieving patient’s symptoms. Patients are usually provided with:

  • Breathing assistance

  • Intravenous fluids, to prevent dehydration

  • Diuretics, to reduce intracranial pressure

  • Anticonvulsants, to prevent seizures

Patients may also benefit from physical therapy, occupational therapy, speech therapy, and psychotherapy to better cope with the complications of their condition.

The prognosis for patients with encephalitis depends on what caused the condition. For example, the death rates for St. Louis and Japanese encephalitis are 30% and 60%, respectively. If herpes encephalitis is left untreated, as many as 75% of patients who have it can die within 18 months.


  • United States. National Institute of Neurological Disorders and Stroke. “NINDS Rasmussen’s Encephalitis Information Page.” Dec. 19, 2011.

  • Bennett JE, et al. Encephalitis. In: Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 8th ed. Philadelphia, Pa.: Saunders Elsevier; 2015.

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