Measles endemicity in insular populations: critical community size and its evolutionary implication.

Abstract Monthly measles case reports from 19 island communities covering periods up to 15 years have been analyzed. Breaks in the continuity of measles transmission were found for all communities of less than 500,000 population. The duration of epidemics was also affected by population density. It is postulated that populations sufficient to support continued propagation of this virus did not exist in primitive societies and that measles virus must have evolved since the development of early civilizations.