Using these little bumps, called fusion proteins, measles enters white blood cells and makes copies of itself. As the white blood cells travel throughout the body, they inadvertently spread the viral particles to organs such as the lungs, liver and, in rare cases, the brain.

In addition to Texas and New Mexico, the Centers for Disease Control and Prevention (CDC) have confirmed measles cases in Alaska, California, Florida, Georgia, Kentucky, New Jersey, New York City, Pennsylvania, Rhode Island and Washington, though the majority are in Texas and New Mexico.