The U.S. declared measles eliminated 25 years ago. But the growing outbreak of the disease centered in West Texas poses a threat to this coveted status—and signals the possibility of measles becoming more common.

As more counties are being impacted by the ongoing measles outbreak and added to the growing list of counties across Texas, here's what to know.

The measles outbreak centered in the South Plains region of Texas grew to 663 cases on Tuesday, according to health officials. The latest update from the Texas Department of State Health Services adds 17 new cases since the agency's last update on Friday.