Brain Infections Inflammation of brain is known as encephalitis. Viruses are the most common reason. Encephalitis can be life-threatening. The most important predictor of survival in such situation is timely diagnosis and treatment. A pus-filled swelling in the brain is called brain abscess and usually occurs when bacteria or fungi enter the brain tissue after an infection or severe head injury. It is a medical emergency. Meningitis is an inflammation of the covering membranes of the brain and spinal cord. The usual infectious agents are bacteria or virus. Some forms of bacterial meningitis are preventable with the vaccinations: Meningitis can be life-threatening, depending on the cause.