Schmallenberg Virus


Schmallenberg virus (SBV) emerged in Northern Europe during summer 2011 and then caused a large epidemic in Europe. It is a negative‐sense single‐stranded RNA virus belonging to the Bunyaviridae family and the Orthobunyavirus genus. SBV affects predominantly domestic and wild ruminants and is transmitted by multiple species of Culicoides biting midges. SBV infection is mainly asymptomatic in adult cattle, sheep and goats but can cause congenital malformations, stillbirths and premature births when infection of the dam occurs at a critical period of gestation. In response to the emergence of SBV, molecular and serological tests have been generated rapidly to diagnose and monitor the disease and a number of inactivated vaccines have been developed.

Key Concepts

  • Schmallenberg virus (SBV) emerged in Northern Europe in summer 2011.
  • SBV belongs to the Bunyaviridae family and the Orthobunyavirus genus.
  • The SBV genome is composed of three negative‐sense single‐stranded RNA segments.
  • SBV is mainly asymptomatic in cattle, sheep and goats.
  • SBV is associated with abortion and birth of malformed or stillborn animals.
  • SBV is an arthropod‐borne virus transmitted by multiple species of Culicoides.
  • Several inactivated vaccines are available.

Keywords: Schmallenberg virus; Orthobunyavirus ; ruminants; emerging viral disease; congenital malformations; arbovirus

Figure 1. SBV morphology and genome organisation. (a) Schematic representation of a bunyavirus particle. The virion is enveloped and spherical with an approximate size of 80–120 nm in diameter. The genome is composed of three negative‐sense single‐stranded RNA segments: large (L), medium (M) and small (S). These segments form complexes with the nucleoprotein and the viral polymerase to constitute the viral RNPs. (b) Schematic representation of the SBV genome. Each viral segment is flanked by identical non‐coding sequences highly conserved between viral species belonging to the Orthobunyavirus genus. These sequences are composed of complementary nucleotides able to pair up to form stable panhandle structures explaining the RNPs helical form in particle.
Figure 2. Orthobunyavirus replication strategy. For the genome replication step, all virion‐sense RNAs (vRNA) are used as templates by the L protein to produce complementary RNA (cRNA). cRNAs are replication intermediates that serve as template to produce neo‐formed vRNAs that will be packaged into new viral particles. mRNA transcription occurs via the same mechanism for all segments. The L protein begins mRNA transcription by a cap‐snatching mechanism, which consist in the cleavage of 5′capped nucleotides from cellular mature mRNAs to prime viral mRNA transcription. (a) L segment mRNA translation leads to the synthesis of the L protein without subsequent maturation steps. (b) M segment mRNA is translated as a polyprotein cleaved into three viral proteins: Gn, NSm and Gc. (c) S segment mRNA is translated in two proteins, N and NSs, by an overlapping reading frame.
Figure 3. SBV transmission cycle. (a) SBV is transmitted by biting midges belonging to the Culicoides genus. These vectors become chronically infected with SBV after a blood meal on an infected animal. Infected vectors are able to spread infection to healthy livestock. (b) In case of adult animal infection, clinical manifestations are mild and associated with a short viraemia detectable from 2 to 6 days post‐infection. (c) When a pregnant female is infected, SBV has the ability to cross the placental barrier to infect several foetal tissues. In a few cases, foetal infection can lead to atypical foetal abnormalities, premature births or stillbirths.


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Further Reading

Carpenter S , Groschup MH , Garros C , Felippe‐Bauer ML and Purse BV (2013) Culicoides biting midges, arboviruses and public health in Europe. Antiviral Research 100: 102–113.

Doceul V , Lara E , Sailleau C , et al. (2013) Epidemiology, molecular virology and diagnostics of Schmallenberg virus, an emerging orthobunyavirus in Europe. Veterinary Research 44: 31.

Walter CT and Barr JN (2011) Recent advances in the molecular and cellular biology of bunyaviruses. Journal of General Virology 92: 2467–2484.

Wernike K , Conraths F , Zanella G , et al. (2014) Schmallenberg virus—two years of experiences. Preventive Veterinary Medicine 116 (4): 423 – 434.

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Doceul, Virginie, Gouzil, Julie, Vitour, Damien, and Zientara, Stéphan(Apr 2015) Schmallenberg Virus. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0024785]