Brain B is transmitted through mosquito bites, the virus has strong neurophagy, incubation period of 10-15 days, most of the patients have mild symptoms or are asymptomatic latent infected, only a few appear central nervous system symptoms, manifested as high fever, impaired consciousness, convulsions, etc. Typical cases can be divided into four stages. Typical cases can be divided into four stages of the general course of the disease, the initial period of high fever, accompanied by nausea, vomiting, some patients have drowsiness, mental lethargy, etc., the course of the disease 1-3 days, the temperature can be as high as 40 ℃ or more, the symptoms gradually worsened, the consciousness of the obvious obstacles, coma can occur. In severe cases, brain parenchymal lesions occur, and central respiratory failure occurs. During and after the recovery period, the body temperature gradually decreases and the mental and neurological symptoms gradually improve. In the sequela period, there are psycho-neurological symptoms after half a year, which are mainly characterized by impaired consciousness, dementia, aphasia, paralysis of limbs, epilepsy, and so on.