Clay's Ark — Octavia E. Butler

EARTH'S FIRST SPACESHIP HAS RETURNED... WITH THE DEATH OF THE ENTIRE PLANET AS ITS CARGO

The one crew member left alive is infected with a terrifying alien plague--and, fight it as he may, he is compelled by that plague to go out and infect others.

And so, in the desert of the American Southwest, a colony is growing of people who are not quite human--and who soon will be unstoppable.