STAT1 and Lassa fever: In a separate study, Yun and colleagues used the STAT1 knock-out (KO) immunodeficient mice as a model for LASV infection, which differs from other immunodeficient mouse strains [24] in their levels of susceptibility to lethal infection with LASV as well as in the development of hepatic and splenic dysfunction, as is often seen in human LF patients [52].