Causative Agent
Measles is caused by an RNA paramyxovirus. Humans are the only natural host. Carriers are not known to occur. The virus remains in the air in droplet form for several hours, especially in humid weather. The infection is transferred from infected secretions of the nose, throat and the respiratory tract, during the prodromal period or the early stages of rash (four days before and five days after the appearance of the rash). Measles affects virtually everyone in infancy or childhood between six months and three years of age in developing countries.

Incubation Period of Measles
The incubation period is commonly 10 days from exposure to the onset of fever, and 14 days to the appearance of rash.