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Diseases & Topics


Encephalitis is irritation and swelling (inflammation) of the brain, most often due to an infection. It is relatively rare. Viral infections are the most common cause of encephalitis. Communicable diseases such as measles, mumps and chickenpox (varicella) can result in encephalitis, as can mosquito-borne viruses (including LaCrosse encephalitis, Eastern equine encephalitis, West Nile virus). Other causes include autoimmune disease, allergic reactions, cancer, and infection with bacteria (such as Lyme disease) or parasites.

Early symptoms of encephalitis may include fever, mild headache, low energy and poor appetite. More severe symptoms include clumsiness or difficulty walking, confusion, drowsiness, irritability, sensitivity to light and vomiting. Other symptoms can include a stiff neck or back. Newborns and young babies may exhibit body stiffness, be irritable and cry more often especially when picked up, may feed poorly and may vomit. Some conditions that cause encephalitis can also cause meningitis, so the symptoms of these conditions can overlap. Symptoms that would require immediate emergency care can include loss of consciousness or stupor, muscle weakness or paralysis, seizures, severe headache and/or a sudden change in mental functions and inability to think clearly. Immediate medical care is essential for emergency symptoms to avoid permanent brain damage, physical impairment or even death. Treatment depends on the cause and the severity of symptoms.

To prevent encephalitis:

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