Encephalitis caused by measles viruses, computer illustration. This virus, from the Morbillivirus group of viruses, consists of an RNA (ribonucleic acid) core surrounded by an envelope studded with surface proteins haemagglutinin-neuraminidase and fusion protein, which are used to attach to and penetrate a host cell. Measles is a highly infectious itchy rash with a fever. It mainly affects children and one attack usually gives life-long immunity. Encephalitis is one of complications of measles infection.