RT Journal Article SR Electronic T1 New World epidemics JF Science JO Science FD American Association for the Advancement of Science SP 788 OP 789 DO 10.1126/science.2305248 VO 247 IS 4944 A1 Sempowski, ML A1 Saunders, LP A1 Bradley, JW YR 1990 UL http://science.sciencemag.org/content/247/4944/788.abstract AB