Encephalitis refers to inflammation of the brain usually due to a viral infection. The inflammation may be focal if it occurs in one section of the brain, multi-focal if it occurs in several different areas or diffuse if it involves the entire brain. Some non-viral causes of encephalitis include Reye’s syndrome, brain abscess and tumors.
The central nervous system consists of the brain and spinal cord. The larger part of the brain is called the cerebrum and the lower portion is termed the brain stem. The cerebrum is responsible for such higher motor functions as, vision, hearing, smell, language, memory and thought. The brain stem is responsible for vital functions including breathing, heart rhythm, sleep and sexual behavior. The spinal cord extends from the base of the skull through the spinal column. Nerves arise from the spinal cord leading to other parts of the body.
In encephalitis, the brain tissue is involved although there also may be evidence of involvement of the meninges, which are tissue membranes that cover the brain. This would be termed meningo-encephalitis. Encephalitis may range in severity from mild to life threatening.
There are many viruses that can cause encephalitis. Up to twenty thousand cases of encephalitis are reported each year in the United States. One of the viruses that can cause encephalitis in adolescents is herpes simplex. This viral agent is the cause of genital herpes. Also the Epstein-Barr virus, which is the cause of mononucleosis, may cause encephalitis, and the varicella-zoster virus may occasionally cause encephalitis in teens. Chickenpox or varicella is caused by the varicella-zoster virus.
Some cases of encephalitis are due Arboviruses. By definition, these viruses are transmitted to humans by the bite of an insect most often a mosquito. The West Nile Virus is an Arbovirus. This virus can be transferred through mosquito bites to humans, horses or birds. In 1999, there was an outbreak of West Nile encephalitis in New York City. Seven individuals died and at least sixty-two people were ill with the virus.
Who is likely to develop encephalitis?
Encephalitis is not a common disease in the United States. Although any age group may be affected, children under age four years, and adults over sixty years appear to be at higher risk. Any individual who is immunocompromised secondary to HIV or cancer treatments, for example, may be at higher risk for encephalitis. Teens who acquire infectious mononucleosis or Chickenpox may have a slight risk for encephalitis. And adolescents who acquired the sexually transmitted illness genital herpes for the first time may also be at risk for encephalitis.
Arboviruses are more prevalent during the warm months when mosquitoes multiply and feed. So individuals who live in certain geographical areas where mosquitoes are more common may have a slightly higher risk for acquisition of viral encephalitis.
What are the symptoms of encephalitis?
In terms of the Arboviruses, symptoms usually occur four to fourteen days after exposure to the mosquito carrying the virus. The symptoms of encephalitis will depend on the age and condition of the teen, the specific virus and the part or parts of the brain involved in the disease.
The early symptoms may include fever, headache, nausea, vomiting and lethargy. As the brain tissue is further affected, the teen may develop changes in the level of consciousness, personality changes, loss of voice, memory and balance functions, seizures and paralysis. If the brain swells and compresses the brain stem, then there may be changes in the teen’s vital functions including respirations and heartbeat.
Encephalitis caused by the herpes virus usually affects the frontal and temporal lobes of the brain. As a result some teens may be left with residual learning disabilities, fine motor control deficits or speech problems. A teen may have a residual seizure disorder from encephalitis due to the varicella-zoster virus.
How is encephalitis evaluated?
If encephalitis is suspected, brain imaging is usually done quickly. A CT or MRI scan can quickly rule out other conditions such as tumors or bleeding into the brain. A spinal tap is usually also performed so that the physician may study the spinal fluid. Studies of the cell types, protein, glucose and fluid pressure are helpful in the evaluation. The fluid may be cultured for microorganisms, and polymerase chain reaction (PCR) may be performed to detect the presence of some viruses including herpes, varicella-zoster and cytomegalovirus. A biopsy of brain tissue may also be performed for further cultures and histological study of the tissue.
How is encephalitis treated?
There is no specific treatment for most cases of encephalitis. Teens with encephalitis need careful and close monitoring of their vital functions including respiration, blood pressure and pulse. Prevention of increased pressure on the brain is exceeding important. Some teens need to be hospitalized in an intensive care unit if the signs and symptoms of encephalitis are serious. Intravenous fluids are usually given, and if seizures occur, then anti-seizure medications are administered.
Acyclovir is a medication that is beneficial in the treatment of encephalitis due to herpes virus. Some authorities suggest that acyclovir should be started in any patient with suspected encephalitis and discontinued unless the patient has encephalitis due to the viruses that cause genital herpes, Chickenpox or mononucleosis. Other antiviral medications have been used under certain situations.
How is encephalitis prevented?
Every adolescent should be up to date on his or her immunizations. Two doses of the Measles-Mumps-Rubella vaccine should prevent most cases of encephalitis due to the measles or mumps virus. One or two doses of Varicella-Zoster vaccine should prevent a case of Chickenpox and resultant encephalitis.
Since herpes virus can be transmitted sexually, all teens should be instructed in safer sex methods including the use of condoms and encouraged to use these methods in every sexual encounter. There is no effective preventive measure against the Epstein-Barr virus.
Since Arboviruses are spread by mosquito bites, then teens who live in or travel to high-risk areas for mosquito bites should follow simple precautions. Mosquito repellant containing the chemical DEET in a concentration no higher than thirty-five percent may help to prevent mosquito bites. This should be reapplied every few hours if the teen is sweating profusely. Adolescents should be especially careful about going outdoors at dawn or at desk when mosquitoes feed more frequently. Other measures to be used include wearing long sleeves and long pants, sleeping in screened areas and removing any sources of standing or stagnant water. And adolescents who plan to travel should contact the Centers for Disease Control and Prevention website <www.cdc.gov/travel> to obtain information about encephalitis risk in the areas they plan to visit.
Related topics:
Herpes, immunizations, meningitis, mononucleosis, mumps, Reye’s syndrome, safer sex, sexually transmitted diseases, travel
