Measles is a common infectious disease, caused by a virus. It involves a characteristic sequence of fever, headache, and malaise followed by conjunctivitis and rhinitis, and then the development of a typical rash, with blotchy erythema, affecting the skin of the face, trunk, and limbs. Cough may indicate infections in small bronchi, and this may progress to viral pneumonia. Secondary bacterial infection may lead to middle ear, infection or pneumonia. Encephalitis, is seen in a small but significant number of cases and is a major justification for vaccination, against this common childhood disease. An abnormal and delayed immunity, to measles virus has been associated with a number of brain diseases, including multiple sclerosis.