EncephalitisEncephalitis 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
viral. They may also be focal (limited to a single location) or generalised (spread throughout the brain). Each year there are several thousand cases reported but, according to the NINDS, 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, enteroviruses, the rabies virus (from an animal bite), or arboviruses – those spread primarily by infected mosquitoes but also by a few ticks.
Humans are not the preferred or primary host of the arboviruses. Most people who are infected have mild to moderate symptoms. Only a very small percentage of people develop encephalitis. Throughout the world, different types of arbovirus-related encephalitis may be seen.
Viral encephalitis may also be seen as a secondary condition that occurs a few weeks after a viral illness.
Bacterial, fungal, and parasitic encephalitis are very rare. Bacterial meningoencephalitis may develop from the bacteria that cause meningitis. Tick-transmitted Lyme disease may cause bacterial encephalitis. Toxoplasma gondii, a parasite associated with cats, can cause parasitic encephalitis in some people with compromised immune systems. Other bacteria, fungi, and parasites can occasionally cause encephalitis.