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INFLAMMATION and INFECTION of the BRAIN. Encephalitis usually results from infection with a VIRUS and is potentially life threatening. Infection can enter the brain via pathogens that are small enough to pass across the BLOOD-BRAIN BARRIER or that are able to follow neural pathways (the routes of nerves) into the brain. The most common cause of encephalitis is infection with an arbovirus transmitted through the bite of a mosquito or tick. Other viruses that typically cause common infections may affect the brain to cause encephalitis, and encephalitis may develop as a complication of viral infection (and less commonly bacterial infection) elsewhere in the body. TOXOPLASMOSIS, a parasitic infection, may also cause encephalitis.
VIRUSES THAT CAN CAUSE ENCEPHALITIS
CYTOMEGALOVIRUS (CMV)California VIRUS
eastern equine virusEPSTEIN-BARR VIRUS
HERPES SIMPLEX virus(HSV) LaCrosse virus
MUMPS virusPowassan virus
RUBELLA virusrubeola (MEASLES) virus
St. Louis virusvaricella zoster viruses
West Nile viruswestern equine virus
Symptoms of Encephalitis and Diagnostic Path
The symptoms of encephalitis differ somewhat in children and in adults. Children often become lethargic, confused, irritable, and sensitive to light; older children may complain of severe HEADACHE. Adults often exhibit changes in mental alertness, cognitive ability, and emotional stability and may have severe headache. Both children and adults may have seizures, FEVER, NAUSEA, and VOMITING.
Diminished awareness or loss of consciousness that accompanies or follows other symptoms of encephalitis is an indication of serious INFECTION that requires urgent medical attention.
The diagnostic path includes LUMBAR PUNCTURE to determine the presence of pathogens or white BLOOD cells, or excessive fluid or increased pressure in the spinal column, any of which may indicate infection. Blood tests may show the presence of certain viruses. Diagnostic procedures such as electroencephalogram (EEG) and COMPUTED TOMOGRAPHY (CT) SCAN or MAGNETIC RESONANCE IMAGING (MRI) can show abnormalities of brain function and structure that are characteristic of encephalitis.
Encephalitis – Treatment Options and Outlook
Mild viral encephalitis generally runs its course within five to seven days and does not require treatment beyond ANALGESIC MEDICATIONS such as acetaminophen to relieve fever and headache. ANTIVIRAL MEDICATIONS can reduce the severity of symptoms and length of illness for some forms of viral encephalitis, notably those resulting from viruses in the herpes family, though have no effect against encephalitis resulting from arboviruses. CORTICOSTEROID MEDICATIONS to suppress the inflammatory response can reduce intracranial swelling and pressure that commonly accompanies encephalitis. Bacterial encephalitis, which is much less common than viral encephalitis and usually a secondary infection, requires treatment with antibiotic medications. Antibiotics are not effective against viral infections.
Recovery depends on the severity of symptoms and the causative PATHOGEN. Though viral encephalitis is generally more mild than bacterial encephalitis, it can be fatal, particularly in infants, the very elderly, and people who are IMMUNOCOMPROMISED. People who have mild encephalitis recover completely and without residual complications. More severe illness may result in permanent brain damage and corresponding cognitive dysfunction, memory impairment, LEARNING DISORDERS, PARALYSIS, SEIZURE DISORDERS, or speech disorders.
Risk Factors and Preventive Measures
The risk for viral encephalitis is greatest during times of the year when mosquito and tick activity is highest, typically May through October in most parts of the United States. Other risks include living in close contact, such as in dormitories and institutions, and infection elsewhere in the body that migrates to the brain. Prevention efforts include public health measures to control mosquito populations and individual efforts to minimize exposure to mosquitoes and ticks.
See also COGNITIVE FUNCTION AND DYSFUNCTION; MEMORY AND MEMORY IMPAIRMENT; MENINGITIS.