They don't have to lock anyone in. The desert there is a fine silicate powder called playa, and when it gets wet it turns into a thick soupy mud. There is no way any vehicle could ever drive in that while it's flooded.

Also, I have heard a better explanation for the reported cases of illness than ebola. More likely the portapotties they are using are leaking into the mud and they are walking around in that. It's trench sickness, which can have similar symptoms to ebola.