Encephalitis B, or epidemic B encephalitis, is an inflammation of the brain parenchyma caused by the B encephalitis virus and is an acute infectious disease of the central nervous system. Epidemic B encephalitis is transmitted by mosquitoes, so it is often prevalent in the summer and fall. Patients with epidemic B encephalitis often present with high fever, impaired consciousness, convulsions, and signs of meningeal irritation, such as headache, vomiting, and cervical ankylosis, etc. Heavy patients often have sequelae of the disease, such as physical impairment, dementia, and unfavorable speech. Epidemic B encephalitis can be divided into four stages: initial, extreme, recovery, and sequelae, with different manifestations in different stages. Most patients have mild or no symptoms at the initial stage, and may experience fever, nausea, vomiting, headache and other discomforts; as the disease progresses, patients with severe disease may exhibit high fever, up to 40°C or more, significant impairment of consciousness, convulsions, etc., which may turn from drowsiness and lethargy to coma. Patients with epidemic B encephalitis can be treated symptomatically, such as anticonvulsant, antipyretic, etc. The disease has a high mortality rate and must be treated actively. Some patients who remain with sequelae need rehabilitation.