Encephalitis - Causes
There are more than a dozen viruses that can cause encephalitis. In some cases, the viruses are spread by direct contact between two people. In other cases, the viruses are transmitted by means of an animal or insect bite. Some common viruses and viral diseases that can cause encephalitis include:
- Chickenpox (see chickenpox entry)
- Measles (see measles entry)
- Mumps
- Epstein-Barr virus
- Cytomegalovirus infection (EBV)
- Human immunodeficiency virus (HIV; see AIDS entry)
- Herpes simplex virus
- Herpes zoster virus (shingles)
- Herpes B virus
- Polio (see polio entry)
- Rabies (see rabies entry)
- Viruses carried by mosquitoes (arboviruses)
Some of these viruses may infect the brain directly. In other cases, the infection spreads from another part of the body, as is usually the case with chickenpox, measles, mumps, rubella (see rubella entry), and Epstein-Barr virus. For example, a person may develop a case of chickenpox, then about five to ten days later, as an immune reaction to the chickenpox virus, the brain becomes inflamed and swollen.
Many forms of encephalitis are spread by the bites of insects or animals. Mosquitoes are common carriers of encephalitis viruses. They carry the viruses in their blood and saliva. When they bite a human, they may transfer the virus to the human's bloodstream. The virus multiplies and spreads throughout the body. When it reaches the brain, it may cause encephalitis.
Dogs, cats, mice, raccoons, squirrels, and bats are also carriers of encephalitis viruses. These animals also carry the virus in their blood and saliva. When they bite a human, they can transmit the virus to the human bloodstream.
- Cerebrospinal fluid:
- Fluid found within the spinal column that is often used to diagnose infections of the central nervous system (the brain and spinal cord).
- Electroencephalogram (EEG):
- A test in which electrical currents in the brain are measured to see if there has been damage to the brain.
- Inflammation:
- A response by the immune system to invasion by a foreign body; signs of an inflammation are redness, heat, swelling, and pain.
- Magnetic resonance imaging (MRI):
- A technique for studying the structure of internal organs by using magnetic waves.
- Vaccine:
- A preparation containing dead or weakened viruses or bacteria to increase a person's immunity (protection) against a certain type of infection.
- Virus:
- A very small organism that can live only within a cell and that can cause some form of disease.
One of the most serious forms of encephalitis is caused by the herpes simplex virus. The herpes simplex virus causes cold sores and genital herpes. Sometimes the herpes virus spreads directly to the brain, causing an encephalitis infection. About 10 percent of all encephalitis cases are caused by this virus. In untreated patients, the rate of death is 70 percent. The rate drops to 15 to 20 percent if patients receive treatment.
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