Adaptation of MARV to severe combined immunodeficiency (scid) mice. Groups of scid mice (n = 10) were infected with ~1000 pfu of wild-type MARV-Ci67, -Musoke, or -Ravn. The livers of two mice from each group were harvested 7–8 days after infection, pooled together, homogenized, and blind-passaged into a new group of naïve scid mice. Blind passaging proceeded until a mean time-to-death of 7–10 days was observed consistently through several passages. (A-C) The remaining eight mice from each group were monitored for survival and the data are presented as the time-to-death for each animal (filled circles) and the mean time-to-death (line). (D-F) The viral titers in the pooled liver homogenates were determined after each passage in scid mice. P15: Passage 15, P10: Passage 10.