Despite the previously reported lethality, in our hands, C. parvum-infected IFNγ-/- mice remained overtly asymptomatic, with infection marked by an acute period of intense oocyst shedding (3- to 8-days post infection (p.i.); reproducibly peaking at approximately one thousand oocysts per milligram of feces). The gene discussed is IFNG; the disease is infection.