Schmallenberg virus (SBV) is an emerging orthobunyavirus of ruminants associated with outbreaks of congenital malformations in aborted and stillborn animals. Since its discovery in November 2011, SBV has spread very rapidly to many European countries. Here, we developed molecular and serological tools, and an experimental in vivo model as a platform to study SBV pathogenesis, tropism and virus-host cell interactions. Using a synthetic biology approach, we developed a reverse genetics system for the rapid rescue and genetic manipulation of SBV. We showed that SBV has a wide tropism in cell culture and “synthetic” SBV replicates in vitro as efficiently as wild type virus. We developed an experimental mouse model to study SBV infection and showed that this virus replicates abundantly in neurons where it causes cerebral malacia and vacuolation of the cerebral cortex. These virus-induced acute lesions are useful in understanding the progression from vacuolation to porencephaly and extensive tissue destruction, often observed in aborted lambs and calves in naturally occurring Schmallenberg cases. Indeed, we detected high levels of SBV antigens in the neurons of the gray matter of brain and spinal cord of naturally affected lambs and calves, suggesting that muscular hypoplasia observed in SBV-infected lambs is mostly secondary to central nervous system damage. Finally, we investigated the molecular determinants of SBV virulence. Interestingly, we found a biological SBV clone that after passage in cell culture displays increased virulence in mice. We also found that a SBV deletion mutant of the non-structural NSs protein (SBVΔNSs) is less virulent in mice than wild type SBV. Attenuation of SBV virulence depends on the inability of SBVΔNSs to block IFN synthesis in virus infected cells. In conclusion, this work provides a useful experimental framework to study the biology and pathogenesis of SBV.

Pestiviruses prevent alpha/beta interferon (IFN-␣/␤) production by promoting proteasomal degradation of interferon regulatory factor 3 (IRF3) by means of the viral N pro nonstructural protein. N pro is also an autoprotease, and its amino-terminal coding sequence is involved in translation initiation. We previously showed with classical swine fever virus (CSFV) that deletion of the entire N pro gene resulted in attenuation in pigs. In order to elaborate on the role of the N pro -mediated IRF3 degradation in classical swine fever pathogenesis, we searched for minimal amino acid substitutions in N pro that would specifically abrogate this function. Our mutational analyses showed that degradation of IRF3 and autoprotease activity are two independent but structurally overlapping functions of N pro . We describe two mutations in N pro that eliminate N pro -mediated IRF3 degradation without affecting the autoprotease activity. We also show that the conserved standard sequence at these particular positions is essential for N pro to interact with IRF3. Surprisingly, when these two mutations are introduced independently in the backbones of highly and moderately virulent CSFV, the resulting viruses are not attenuated, or are only partially attenuated, in 8-to 10-week-old pigs. This contrasts with the fact that these mutant viruses have lost the capacity to degrade IRF3 and to prevent IFN-␣/␤ induction in porcine cell lines and monocyte-derived dendritic cells. Taken together, these results demonstrate that contrary to previous assumptions and to the case for other viral systems, impairment of IRF3-dependent IFN-␣/␤ induction is not a prerequisite for CSFV virulence.

The modified proportional margins system resulted in satisfactory local disease control in dogs with MCTs.

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To the authors' knowledge, this is the first report of acquired scoliosis in an alpaca, which appears to represent an unusual manifestation of parelaphostrongylosis that was reported in horses.