The most common signs of acute viral encephalitis are fever, headache, and a change in level of consciousness.
Other common signs are the eyes becoming sensitive to light (photophobia), confusion, and sometimes seizures.
Meningitis may sometimes occur with encephalitis. Meningitis is the inflammation of the membranes (meninges) surrounding the brain and spinal cord. Stiffness of the neck is the cardinal sign of meningitis, and occurs in addition to the symptoms of encephalitis.
Some people exposed to insect-borne encephalitis viruses do not develop symptoms of encephalitis. They may only experience low-grade fever, drowsiness, and flu-like symptoms of malaise (general feeling of illness) and myalgia (muscle aches). Headache, vomiting, and sensitivity to light may follow.
Some viruses may affect specific areas of the brain, including problems with speech, movement, and behavioral (personality) changes. Epstein-Barr virus, St. Louis encephalitis, eastern equine encephalitis, and enterovirus infections can have different symptoms, depending on the part(s) of the brain affected.
Herpes simplex encephalitis is known to cause additional symptoms. Fever, headache, decreased level of consciousness, and confusion may occur. Other symptoms may include seizures, difficulty speaking, inability to move one side of the body, memory loss, and/or behavioral changes.
Rabies may produce symptoms days to months after the exposure.
Frequently there is pain, numbness, or tingling at the bite wound. It may take 30-70 days after exposure for rabies symptoms to begin. Because of this, sometimes the patient cannot recall a bite or animal exposure. Early symptoms over the first 5-7 days of illness include fever, malaise, nausea, vomiting, and headache. Behavioral symptoms may also appear, including anxiety, depression, delirium (sudden confusion and change in mental status), hallucinations, and intolerance to touch, sounds, and visual stimuli. Later symptoms include agitation, muscle spasms, and fear of the sight of water (hydrophobia). It may become difficult to swallow liquids or saliva. Eventually, coma and death will occur. Some patients with rabies have paralysis that begins in the legs and moves upward to involve the arms, eventually leading to coma.
Crowded living conditions and poor sanitation can increase the risk of some types of encephalitis. Contact with infected animals can put humans at risk of encephalitis.
Some viruses are transmitted between humans by respiratory (airborne) and intestinal-borne routes. Measles, mumps, and chickenpox are examples of respiratory viruses. Poliovirus, coxsackie, and echovirus are examples of intestinal viruses. Frequent and thorough hand washing with soap and water can decrease the spread of viruses and other illness-causing germs.
Living in or traveling to an area where insects are known to carry encephalitis-causing viruses increases your risk for getting insect-borne encephalitis. In the U.S., you are most likely to get insect-borne encephalitis between June and October.
The months when risk of insect-transmitted viral infection is highest can vary, depending on the geographical region and the prevalence of mosquitoes and ticks that season.
Older people are at a greater risk of serious disease and death from West Nile and St. Louis encephalitis. However, California encephalitis poses a greater danger to children under 15 years of age than to older people. Having a weakened immune system puts you at risk for many types of encephalitis.
For example, people with weakened immune systems due to HIV are at higher risk for infection from many viruses that cause encephalitis. Similarly, transplant recipient patients who must be given medication to prevent organ or tissue rejection are more vulnerable to organisms that cause viral encephalitis.
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