CAUSE AND MODE OF SPREAD

The germ which causes measles has not been certainly isolated but it is known to be in the secretions from the respiratory mucous membrane. It is there in the earliest stages of the disease, two or three days before the skin eruption appears, and it disappears when the eruption fades. The danger of spreading the disease is therefore present very early, before the eruption develops, and it is soon over, having passed when fever has been absent a couple of days. The germs pass from the sick to others in the secretions from the respiratory tract. In coughing and sneezing small particles of infected mucus are thrown out into the air as mouth spray and the inhalation of these causes infection. Outside the body the germs quickly die. They do not survive drying and exposure to the sunlight. Transfer of the disease by a third person or by any mechanical carrier can only occur if it is done quickly. The particles of moist secretion which convey the infection may be very small and may be carried several feet in the air. Thus a susceptible individual may be infected by coming into a room with a case of measles although never approaching very close. Similarly a child coming down with measles while in school may sow the germs widely among other pupils.