'Schmallenberg virus'--a novel orthobunyavirus emerging in Europe

Abstract

In 2011, a novel orthobunyavirus of the Simbu serogroup, the Schmallenberg virus (SBV), was discovered using a metagenomic approach. SBV caused a large epidemic in Europe in ruminants. As with related viruses such as Akabane virus, it appears to be transmitted by biting midges. Transplacental infection often results in the birth of malformed calves, lambs and goat kids. In more than 5000 farms in Germany, The Netherlands, Belgium, France, UK, Italy, Spain, Luxembourg, Denmark and Switzerland acute infections of adult ruminants or malformed SBV-positive offspring were detected, and high seroprevalences were seen in adult ruminants in the core regions in The Netherlands, Germany and Belgium. The discovery of SBV, the spread of the epidemic, the role of vectors, the impact on livestock, public health issues, SBV diagnosis and measures taken are described in this review. Lessons to be learned from the Schmallenberg virus epidemic and the consequences for future outbreaks are discussed.

Fig. 1.

Cattle, sheep and goat holdings with Schmallenberg virus cases in Germany (as of 27 August 2012).

Fig. 2

[colour online]. Schmallenberg virus-positive detections (real-time RT–PCR of brain samples) in notified farms in The Netherlands (2011–2012).

Fig. 3.

Likely period of infection of pregnant sheep with Schmallenberg virus (SBV) in Germany in 2011 compared to case counts of BTV-8 in 2006 and 2007. Seventeen weeks were deducted from the reported date of birth of malformed lambs with confirmed SBV infection to calculate the most likely time of transplacental infection (assumptions: duration of pregnancy in sheep 150 days (range 145–155) days; risk period for SBV infection days 25–38 of pregnancy with the highest risk on day 32). Spearman's rank correlation: adjusted SBV outbreaks in sheep vs. BTV-8 in 2006: ρ = 0·894, P = 1·264 × 10⁻¹¹; adjusted SBV outbreaks in sheep vs. BTV-8 in 2007: ρ = 0·857, P = 7·484 × 10⁻¹⁰.