DNS4 BTV mutants are pathogenic in mice models of disease Next, we assessed the virulence of DNS4 BTV mutants in two murine models of bluetongue infection [46, 47] . 129sv IFNAR (2/2) mice, which are deficient in the type I IFN receptor, are susceptible to infection and disease induced by BTV inoculated by various routes [46, 48] . Newborn NIH-Swiss mice inoculated intracerebrally are also susceptible to BTV infection [47] . These models have been previously used to assess BTV virulence [47, 49] .