Measles is caused by the measles virus (a virus in the paramyxovirus family), which occurs in humans everywhere in the world, except where almost 100% of the population has been vaccinated.
Measles (rubeola) is highly contagious and almost everyone coming into contact with an infectious person will contract the disease, unless they have had measles before or have been vaccinated.
If a person who hasn’t been vaccinated comes into contact with someone who is infected with measles and breathes in droplets that contain the virus, they will rapidly become infected with the virus. Ninety percent of people who haven’t been vaccinated against measles will get the virus if they’re in contact with an infected person.
The spread of the disease from person to person is assisted by the fact that a runny nose with sneezing and coughing occurs in the early stages of the illness. A person is infectious from about 3 days before the rash appears and up to 5 days after its appearance.
Reviewed by Prof Eugene Weinberg, Paediatrician at the University of Cape Town’s Allergy and Immunology Unit. April 2018.