Three hundred and twenty-one cases have been reported in the ongoing measles outbreak in Texas, New Mexico and Oklahoma, the states said Tuesday. This is an increase of 25 cases since an update on Friday.

A total of 321 cases have been reported in the outbreak, which began earlier this year in Gaines County, Texas

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.