Robert Ludlum's The Ares decision / Kyle Mills.

Enhanced descriptions from Syndetics:

In northern Uganda, an American special forces team is decimated by a group of normally peaceful farmers. Video of the attack shows even women and children possessing almost supernatural speed and strength, consumed with a rage that makes them immune to pain, fear, and all but the most devastating injuries.

Covert-One's top operative, army microbiologist Colonel Jon Smith, is sent to investigate the attack and finds evidence of a parasitic infection that for centuries has been causing violent insanity and then going dormant. This time, though, it's different. The parasite had been purposely kept alive and crudely transmitted in acts of terrorism. Now the director of Iranian Intelligence is in Uganda trying to obtain this biological weapon to unleash it on the West.

Smith and his team are ambushed and cut off from all outside support just as they begin to suspect that forces much more powerful than the Iranians are in play-forces that can be traced to Washington itself.