Clay's Ark by Octavia Butler
An innocent familiy, carjacked on a desolate highway, is abducted to a bizarre new world. A world being born in the Californian desert.
They discover Earth has been invaded by an alien microorganism. The deadly entity attacks like a virus, but survivors of the disease genetically bond with it, developing amazing powers, near-immortality, unnatural desires - and a need to spread the contagion and create a secret colony of the transformed. Now the meaning of "survival" changes. For the babies born in the colony are clearly, undeniably, not human...
Third from Patternmaster series