IRGM and infection: Including Irga6, four mouse IRG genes have now been disrupted and all have resulted in a more or less dramatic susceptibility to infection with T. gondii. With mice on a mixed C57BL/6 129Sv background 100% death within 14 days was seen after i.p. infection with 20 cysts of the mouse-avirulent ME49 strain T. gondii in Irgm3−/− and Irgm1−/− mice [23], [49].