Oliveros virus (OLV) is an arenavirus hosted by the sigmodontine rodent, Necromys benefactus, in central Argentina. We report a 3-year longitudinal field study of the dynamics of OLV infection in host populations from 15 localities in two provinces on the central Argentine pampa. There was an overall 3-year period immunofluorescent antibody prevalence of 25% in the host population, and infected hosts were found throughout the study area. Spill-over infection into common sympatric species was rare. Infection dynamics exhibited many of the patterns seen for other rodent-borne arenaviruses and hantaviruses, but had some unique characteristics. Host population density was highest in autumn and lowest in spring, while antibody prevalence was highest in spring and lowest in autumn. Virus transmission was horizontal: infection was strongly associated with age, reaching 45% prevalence in the oldest individuals, and prevalence of infection was equal among male and female hosts. Infection may have been associated with scars, which were also approximately equally distributed among male and female Necromys.