It’s nearly midday when brice bidja steps out of the tangled forest surrounding the African village of Messok in southeastern Cameroon, gripping a Russian 12-gauge shotgun in one hand and the limp body of a mustached monkey in the other. Bidja usually returns alone after his hunts, but on this morning a handful of foreigners tags along with him as he approaches his mud-brick hut. Among the researchers, logisticians, and documentarians is American virologist Nathan Wolfe.

Wolfe stands just outside as the others duck through the low doorway; inside, the glare of the tropical sun gives way to an easy reddish glow of firelight on the faces of Bidja’s wife Sandrine and their two small children. Bidja sets the monkey down on a palm frond and pulls out a sheet of filter paper provided by Wolfe’s organization, the Global Viral Forecasting Initiative (GVFI). Sandrine crouches and picks up a machete, then slices off one of the animal’s front legs and holds it over the paper, aiming the dripping blood at five printed circles. Once the targets are saturated, the hunter tucks the blood sample into a ziplock bag filled with silica gel packets and hands the bag to one of Wolfe’s colleagues. The group will run tests later to see if the animal that Bidja and his family would soon devour is infected with a particularly nasty virus that could jump to humans. ultimately becoming the next deadly pandemic...