pediatrics
Measles
Pathophysiology of Measles
Measles is caused by a paramyxovirus and is a human disease with no known animal reservoir or asymptomatic carrier state. It is extremely communicable; the secondary attack rate is>90% among susceptible people who are exposed. Measles is spread mainly by secretions from the nose, throat, and mouth during the prodromal or early eruptive stage. Communicability begins several days before and continues until several days after the rash appears. Measles is not communicable once the rash begins to desquamate. Transmission is typically by large respiratory droplets that are discharged by cough and briefly remain airborne for a short distance. Transmission may also occur by small aerosolized droplets that can remain airborne (and thus can be inhaled) for up to 2 hours in closed areas (eg, in an office examination room). Transmission by fomites seems less likely than airborne transmission because the measles virus is thought to survive only for a short time on dry surfaces. An infant whose mother has immunity to measles (eg, because of previous illness or vaccination) receives antibodies transplacentally; these antibodies are protective for most of the first 6 to 12 months of life. Lifelong immunity is conferred by infection. In the United States, almost all measles cases are imported by travelers or immigrants, with subsequent community transmission occurring primarily among unvaccinated people. 