sumption of decreasing virulence with time is a double-edged sword in NativeAmerican disease history. Recent Native Americans have extreme susceptibility to oftenacute infections such as influenza and tuberculosis (Indian Health Service 1999; Koenig1921; Matthews 1886). Although, as detailed later in this paper, many factors, includingsocio-economic conditions, diet, and other concurrent infections, could be contributing tothis incidence, these factors seem to pale by comparison with disease history. Essentially,current incidence rates account for the absence of crowd infections prior to Columbus andabsence explains the present incidence rate

se diseases, once introduced, severelywinnowed Native American populations.

Since the mid-twentieth century it has been widely accepted that Old World populationsintroduced infectious diseases to Native Americans beginning with the Columbianvoyages of AD 149