In Randy Shilts’ history of AIDS, “And the Band Played On,” he tells the story of an Air Canada steward named Gaëtan Dugas, who suffered from what Dugas called “gay cancer” and infected 40 people or more with HIV. He was, Shilts wrote, “Patient Zero.” Modal TriggerDugas, through his extensive travels and unrepentant, unprotected sex even after he was diagnosed, undoubtedly helped spread AIDS. But was he the man who brought the disease to America? In the new book, “The Chimp and the River: How AIDS Emerged from an African Rain Forest” (W.W. Norton), author David Quammen says no.