 Lymphocytic encephalitis is an actual disease caused by the  Lymphocytic Choriomeningitis Virus. Encephalitis is the acute  inflammation of the brain. Brain damage and death can occur as a  result of the inflammation. As Doc Cottle stated in the episode, it  is usually carried and transmitted by rodents. Unlike the Colonial  survivors, humans on Earth are not immune, although infection does  not result in symptoms in most healthy adults. It can, however, be  deadly for persons with compromised immune systems.