A poliomyelitis epidemic apparently occurred in about 1936 in an almost totally isolated population of forest-dwelling Amerindians, suggesting that endemic poliomyelitis may have been present prior to sustained contact with urban populations.
(JAMA 230:1295-1297, 1974)
Lewis TH, Brannon WL. Poliomyelitis in an Isolated Amerindian Population. JAMA. 1974;230(9):1295-1297. doi:10.1001/jama.1974.03240090035021