Robert Ludlum's The Ares Decision

When a U.S. Special Forces team is wiped out by a group of normally peaceful farmers in Uganda, Covert-One operative Jon Smith is sent to investigate. 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. Smith finds evidence of a parasitic infection that for centuries has been causing violent insanity and then going dormant. This time, though, it's different.