Measles is a respiratory virus that can survive in the air for up to two hours. Up to 9 out of 10 people who are susceptible will get the virus if exposed, according to the U.S. Centers for Disease Control and Prevention.

An ongoing measles outbreak that began in one of Texas' least vaccinated counties has mushroomed to 90 cases across a cluster of seven counties in the state, according to an update by the Texas Department of State Health Services on Friday.

The Mennonite population being affected by a measles outbreak in West Texas is part of a larger, loosely affiliated group of churches worldwide with varied beliefs and leadership structures — and with