Plastic model of the Measles virus designed from electron micrographs.Although round, the measles virus is classed as a cubic form. There is an outer envelope studded with small spiky projections. The coiled rope formation inside is the capsid, taking this shape instead of the box-like shell seen in some viruses. The nucleic acids which carry the genetic code of the virus are wound in a spiral inside the cord-like capsid. Measles virus (MeV) is a single-stranded, negative-sense, enveloped (non-segmented) RNA virus of the genus Morbillivirus within the family Paramyxoviridae. Humans are the natural hosts of the virus; no animal reservoirs are known to exist. The measles virus is the cause of measles, an infection of the respiratory system. Symptoms include fever, cough, runny nose, red eyes and a generalized, maculopapular, erythematous rash. The virus is highly contagious and is spread by coughing and sneezing via close personal contact or direct contact with secretions. Rubella (German measles) and roseola are different diseases.