Encephalitis means inflammation of the brain. It can be caused by bacterial infections and, most often, viral infections.
Several thousand cases of encephalitis are reported each year, but many more may actually occur, since the symptoms may be mild to non-existent in most patients.
There are two types of the condition:
- Primary encephalitis (also called acute viral encephalitis) is caused by a direct viral infection of the spinal cord and brain. The infection may be focal (located in only one area) or diffuse (located in many different areas).
- Secondary encephalitis (also known as post-infective encephalitis) can result from complications of a current viral infection. When this type results from an immunization or earlier viral infection, it is known as acute disseminated encephalitis. This illness often occurs two to three weeks following the initial infection.
Most cases of encephalitis in the United States are caused by:
- Enteroviruses
- Herpes simplex virus types 1 and 2
- A bite from a rabid animal (rabies virus)
- Arboviruses, which are transmitted from infected animals to humans through the bite of an infected tick, mosquito, or other blood-sucking insect.
Lyme disease, a bacterial infection spread by tick bite, can also cause it.
Anyone can get it. People with weakened immune systems, including those with
HIV or those taking immunosuppressant drugs, are at the highest risk of contracting encephalitis.
The brain inflammation caused by encephalitis can produce a wide range of symptoms, including:
- Sudden fever
- Headache
- Vomiting
- Heightened sensitivity to light
- Confusion and impaired judgment
- Drowsiness
- Weak muscles
- Clumsy and unsteady gait
- Irritability.
Symptoms that might require emergency treatment include:
(Click Encephalitis Symptoms for information on other symptoms of the condition.)
Complications Resulting From Encephalitis
In extreme cases of encephalitis, complications can include:
Encephalitis treatment may involve antiviral medications being prescribed for
herpes encephalitis or other severe viral infections. Anticonvulsants are used to prevent or treat seizures. Corticosteroids are used to reduce brain swelling and inflammation. Sedatives may be needed for irritability or restlessness. Over-the-counter medications may be used for fever and
headache. Individuals with encephalitis or
bacterial meningitis are usually hospitalized for treatment.
The prognosis varies depending on the
cause of encephalitis. Some cases are mild, short, and relatively benign, with patients having a full recovery. Other cases are severe, possibly leading to permanent impairment or even death.
The acute phase of encephalitis may last for one to two weeks, with gradual or sudden resolution of fever and neurological symptoms. Neurological symptoms may require many months before full recovery.
Current research efforts include gaining a better understanding of how the central nervous system responds to inflammation and the role of T cells (blood cells involved in immune system response) in suppressing infection in the brain.
Scientists hope to better understand the molecular mechanisms involved in the protection and disruption of the blood-brain barrier, which could lead to the development of new treatments for several neuroinflammatory diseases such as
meningitis and encephalitis.
Other scientists hope to define, at a molecular level, how certain viruses overcome the body's defense mechanism and interact with target host cells.
A possible treatment under investigation involves testing neuroprotective compounds that block the damage that accumulates after the inflammation of encephalitis. (This damage can lead to potential complications including
dementia and loss of cognitive function.)
