Among the several forms of viral brain inflammation are rabies, polio, and two types transmitted by the mosquito: equine encephalitis in its various forms and St. Louis encephalitis. The latter two have appeared in epidemic form in the United States and are characterized by high fever, prolonged coma (which is responsible for the disease being known as a "sleeping sickness"; see also trypanosomiasis), and convulsions sometimes followed by death. Encephalitis that results as a complication of another systemic infection is known as parainfectious encephalitis and can follow such diseases as measles (rubeola), influenza, and scarlet fever. The AIDS virus also infects the brain and produces dementia in a predictably progressive pattern. Although no specific treatment can destroy the virus once the disease has become established, many types of encephalitis can be prevented by immunization.
Inflammation of the brain, most often due to infection, usually with a virus. One class of encephalitis (including multiple sclerosis) attacks the myelin sheath that insulates nerve fibres rather than the neurons themselves. In most cases, symptoms include fever, headache, lethargy, and coma. Convulsions are most common in infants. Characteristic neurological signs include uncoordinated, involuntary movements and localized weakness. The symptoms and a lumbar puncture (to obtain cerebrospinal fluid for analysis) may establish the presence but not the cause. Treatment usually aims to relieve the symptoms and ensure quiet rest. Various symptoms may remain after recovery.
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Encephalitis may be caused by a variety of afflictions. One such affliction is rabies. Encephalitis may also be caused by HIV. The major causes of encephalitis outbreaks all over the world are viruses like Japanese Encephalitis, West Nile, Chandipura virus, St. Louis Encephalitis, Equine Encephalitis, La Crosse encephalitis, Murray Valley encephalitis virus, California encephalitis virus, Tick-borne meningoencephalitis, Herpes simplex, Influenza A virus. Less common are e.g. RSSE (Russian spring-summer encephalitis) viruses.
Neurological examinations usually reveal a drowsy or confused patient. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningeoncephalitis. Examination of the cerebrospinal fluid obtained by a lumbar puncture procedure usually reveals increased amounts of protein and white blood cells with normal glucose, though in a significant percentage of patients, the cerebrospinal fluid may be normal. CT scan often is not helpful, as cerebral abscess is uncommon. Cerebral abscess is more common in patients with meningitis than encephalitis. Bleeding is also uncommon except in patients with herpes simplex type 1 encephalitis. Magnetic resonance imaging offers better resolution. In patients with herpes simplex encephalitis, electroencephalograph may show sharp waves in one or both of the temporal lobes. Lumbar puncture procedure is performed only after the possibility of prominent brain swelling is excluded by a CT scan examination. Diagnosis is often made with detection of antibodies in the cerebrospinal fluid against a specific viral agent (such as herpes simplex virus) or by polymerase chain reaction that amplifies the RNA or DNA of the virus responsible (such as varicella zoster virus).
Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1917 to 1928, resulting in millions of deaths worldwide. Those who survived sank into a semi-conscious state that lasted for decades until the Parkinsons drug L-dopa was used to revive those still alive in the late 1960s by Oliver Sacks.
There have been only a small number of isolated cases in the years since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be either a bacterial agent or an autoimmune response following infection.
Herpes simplex encephalitis is caused by the herpes simplex virus that manifests in oral cold sores or genital sores. When this triggers brain inflammation, which occurs in 10% of cases of encephalitis (2 cases per million people), half of all untreated patients die (1 case per million people). Brain damage, partial paralysis, seizures, hallucinations and an altered state of consciousness are all common symptoms. HSE can be passed from mother to child during birth in rare cases, where symptoms include lethargy, tremors, irritability, seizures and poor feeding in the first two weeks after birth.