The troop / Nick Cutter.

Enhanced descriptions from Syndetics:

WINNER OF THE JAMES HERBERT AWARD FOR HORROR WRITING
" The Troop scared the hell out of me, and I couldn't put it down. This is old-school horror at its best." --Stephen King

Once every year, Scoutmaster Tim Riggs leads a troop of boys into the Canadian wilderness for a weekend camping trip--a tradition as comforting and reliable as a good ghost story around a roaring bonfire. The boys are a tight-knit crew. There's Kent, one of the most popular kids in school; Ephraim and Max, also well liked and easygoing; then there's Newt the nerd and Shelley the odd duck. For the most part, they all get along and are happy to be there--which makes Scoutmaster Tim's job a little easier. But for some reason, he can't shake the feeling that something strange is in the air this year. Something waiting in the darkness. Something wicked...

It comes to them in the night. An unexpected intruder, stumbling upon their campsite like a wild animal. He is shockingly thin, disturbingly pale, and voraciously hungry--a man in unspeakable torment who exposes Tim and the boys to something far more frightening than any ghost story. Within his body is a bioengineered nightmare, a horror that spreads faster than fear. One by one, the boys will do things no person could ever imagine.

And so it begins. An agonizing weekend in the wilderness. A harrowing struggle for survival. No possible escape from the elements, the infected...or one another.

Part Lord of the Flies , part 28 Days Later --and all-consuming--this tightly written, edge-of-your-seat thriller takes you deep into the heart of darkness, where fear feeds on sanity...and terror hungers for more.