The Troop by Nick Cutter

Once a year, scoutmaster Tim Riggs leads a troop of boys into the Canadian wilderness for a three-day camping trip; a tradition as comforting and reliable as a good ghost story and a roaring bonfire. But when an unexpected intruder — shockingly thin, disturbingly pale, and voraciously hungry — stumbles upon their campsite, Tim and the boys are exposed to something far more frightening than any tale of terror. The human carrier of a bioengineered nightmare. An inexplicable horror that spreads faster than fear. A harrowing struggle for survival that will pit the troop against the elements, the infected … and one another.