IFN-γ plays a crucial role in early protective immune responses against a virulent North American isolate of WNV [23] and mouse-adapted strains of dengue virus [24, 25], but is dispensable in the control of infection with less virulent strains of WNV [26] or yellow fever virus [27, 28], and shows only a modest protective role against Murray Valley encephalitis [29]. The gene discussed is IFNG; the disease is infection.