Encephalitis is an inflammation of the brain that can be caused by bacterial or viral infections. Although anyone can get encephalitis, people with weakened immune systems, including those with HIV or those taking immunosuppressants, are at the highest risk of contracting encephalitis. There are two types of encephalitis: primary encephalitis, which is caused by a direct viral infection of the spinal cord and brain, and secondary encephalitis, which results from complications of a current viral infection. Some symptoms of encephalitis can include a sudden fever, a headache, and vomiting.