Measles virus of the genus Morbillivirus of the family Paramyxoviridae.
Transmission, which is primarily by large respiratory droplets, increases during the late winter and early spring in temperate climates and after the rainy season in tropical climates.
Nature of the disease
Measles is a highly contagious infection; before vaccines became available, this disease had affected most people by the time of adolescence. Common complications include middle-ear infection and pneumonia. High-risk groups for measles complications include infants and individuals suffering from chronic diseases and impaired immunity, or from severe malnutrition (including vitamin A deficiency).
Measles occurs in a seasonal pattern. However, following the introduction of large-scale measles immunization, far fewer cases now occur in industrialized countries and indigenous transmission has virtually stopped in the Americas. Epidemics may still occur every 2 or 3 years in areas where there is low vaccine coverage. In countries where measles has been largely eliminated, cases imported from other countries remain an important continuing source of infection. In 2009, worldwide measles vaccination coverage had reached 82%, and between 2000 and 2008 the estimated annual number of deaths from measles dropped from 733 000 to 164 000.
Risk for travellers
Travellers who are not fully immunized against measles are at risk.