Knowledge center. Measles, also known as Rubeola or morbilli, is a highly infectious illness caused by a virus-a viral infection caused by the rubeola virus. Measles is an endemic disease; meaning it is continually present in a community and many people develop resistance.nowledge center. Measles, also known as Rubeola or morbilli, is a highly infectious illness caused by a virus-a viral infection caused by the rubeola virus. Measles is an endemic disease; meaning it is continually present in a community and many people develop resistance.