Encephalitis is an acute infection of the brain characterized by
fever, headache, and an altered state of consciousness, with or
without seizures. Most cases of encephalitis are caused by
viruses. They may also be limited to a single location (focal)
or diffuse throughout the brain (generalized). Each year there
are several thousand cases reported but, according to the
National Institute of Neurological Disorders and Stroke, there
are probably many more cases with minimal to mild symptoms that
occur but are not documented. Viral encephalitis may be caused
by a variety of viruses including: - Herpes simplex virus - The
rabies virus (from an animal bite) - Arboviruses – those spread
primarily by infected mosquitoes but also by a few ticks Most
people who are infected have mild to moderate symptoms. Only a
very small percentage of people develop encephalitis. In the
United States, West Nile Virus is the most common cause of
arbovirus encephalitis. Other more rare U.S. arboviruses are
distributed geographically.