Measles is caused by a highly contagious virus that’s airborne and spreads easily when an infected person breathes, sneezes or coughs. It is preventable through vaccines, and has been considered eliminated from the U.S. since 2000.

New Mexico health officials announced that the measles outbreak has reached a third county in the state’s southeastern corner Tuesday.

An unvaccinated child in Chaves County, NM has been diagnosed with measles, marking the third county in New Mexico affected by the ongoing outbreak.

Texas confirmed 505 measles cases in 22 counties on Tuesday. About 70% of these cases were confirmed in children under the age of 18.

The multistate outbreak confirms health experts’ fears that the virus will take hold in other U.S. communities with low vaccination rates.

West Texas is in the middle of a still-growing measles outbreak with 505 cases reported on Tuesday. The state expanded the number of counties in the outbreak area this week to 10. The highly contagious virus began to spread in late January and health officials say it has spread to New Mexico,

A public health official in Texas recently warned that the state's ongoing measles outbreak could last a year. Why are cases expected to keep rising?

Update: Texas faces a growing measles outbreak, with additional counties put on alert as cases rise to 505 with two school-aged fatalities; vaccination is urged

have doubled.