Schmallenberg Disease-A Newly Emerged Culicoides-borne Viral Disease of Ruminants

Abstract

First appearing in 2011 in Northern Europe, Schmallenberg virus (SBV), an Orthobunyavirus of the Simbu serogroup, is associated with clinical disease mainly in ruminants such as cattle, sheep and goats. The clinical signs are characterized by abortion and congenital deformities in newborns. The virus is transmitted by Culicoides midges of the Obsoletus complex. SBV infection induces a solid protective immunity that persists for at least 4 or 6 years in sheep and cattle, respectively. SBV infection can be diagnosed directly by real-time RT-qPCR and virus isolation or indirectly by serological assays. Three vaccines are commercially available in Europe. This article provides a comprehensive literature review on this emerging disease regarding pathogenesis, transmission, diagnosis, control and prevention. This review also highlights that although much has been learned since SBV's first emergence, there are still areas that require further study to devise better mitigation strategies.

Keywords: Culicoides; Schmallenberg virus; ruminants.

Figure 1

Schmallenberg virus (SBV) virion and genome organization. (A) The SBV large (L), medium (M), and small (S) segments are present in the virion and encapsulated with an envelope lipid bilayer containing the surface glycoproteins Gn and Gc. (B) Schematic representation of the SBV segments and the SBV coding strategy: L-segment: L, RNA-dependent RNA polymerase protein; M-segment: Gn and Gc, glycoproteins Gn and Gc; NSm, non-structural protein; S-segment: N, nucleoprotein; NSs, non-structural protein.