Transmission electron micrograph of a brain cell nucleus being completely overrun with replicating measles virus. The viral genome has been released from the virus particles and uses the cell's own machinery to help it replicate. If the brain becomes infected with measles the resulting encephalitis can cause seizures, epilepsy, deafness, coma, mental retardation or death. Encephalitis is a complication of measles that occurs in 1 in 1000 cases. Supplied by Mike Kayser, courtesy of Wellcome Images.