Cause of Measles
A very contagious disease, measles is caused by an infection with the measles virus. Transmission of the virus occurs through the coughing and sneezing of an infected person. If one person has it, 90 percent of their susceptible close contacts will also become infected with the measles virus.
Measles virus is a Paramyxovirus, of the genus Morbillivirus. It is single-stranded RNA virus, and is closely related to the rinderpest and canine distemper viruses. Measles virus is rapidly inactivated by heat, light, acidic pH, ether, and trypsin (an enzyme). It has a short survival time (under 2 hours) in the air, on objects, and on surfaces. The measles virus only infects humans.
Prior to 1963, almost everyone got measles; it was an expected life event. Each year in the United States, there were approximately 3 to 4 million cases, and an average of 450 deaths. Epidemic cycles occurred every 2 to 3 years. More than half the population had measles by the time they were 6 years old, and 90 percent had the disease by the time they were 15 years old. This indicates that many more cases were occurring than were being reported; however, after the measles vaccine became available, the number of measles cases dropped by 99 percent, and the epidemic cycles diminished drastically.
Today, about one quarter of measles cases occur in adults, and nearly half are in unvaccinated children, mostly minorities.
Measles is very contagious. The measles virus is spread by coughing and sneezing. Measles transmission can occur any time, from about 4 days prior to the onset of the rash to 4 days after the onset. If one person has it, 90 percent of their susceptible close contacts will also become infected with the measles virus.