Evergreen — Bruce Golden

The planet Evergreen is ripe for exploitation, and corporate Earth is only to happy to harvest the lush timber and mining resources to provide luxury goods for a world whose own resources were long ago eradicated.
Like the frontier towns of early America, Evergreen draws the misfits, the outcasts, the unwanted of Earth, who exist as little more than slaves to pay off the huge costs of their trip to this magnificent wilderness. But others have come as well--a priest obsessed with finding the City of God, an exobiologist convinced she has found what may be the next species capable of reaching true sentience, an archaeologist whose young wife is torn between her love for him and her lust for her stepson.
There is one other player in this game of greed and desire, however. And that player has grown more and more certain that the creatures that have infected it must be destroyed.