A child born in the first month of life may get encephalitis. Encephalitis refers to an infection of the brain parenchyma, which may be caused by a direct invasion of the brain tissue by a pathogen or by an immune response during infection in certain acute or chronic diseases, and may present with fever, altered mental status, and increased or decreased muscle tone in the child. Infants and children are the most commonly affected by encephalitis, so the possibility of infection leading to encephalitis exists in children in the first month of life. When a child develops high fever, altered mental status, and neurological symptoms such as convulsions and is suspected of having encephalitis, he or she should go to a regular hospital in time.