Introduction
Schmallenberg virus (SBV), an orthobunyavirus belonging to the Simbu serogroup that predominantly infects ruminants, emerged in Central Europe in 2011 (Hoffmann et al., 2012). The virus is transmitted between its mammalian hosts by hematophagous insect vectors (Culicoidesbiting midges) (Elbers, Meiswinkel, van Weezep, Sloet van Oldruitenborgh-Oosterbaan, & Kooi, 2013; Sick, Beer, Kampen, & Wernike, 2019). Examination of Culicoides spp. caught in Denmark during the initial spread of SBV in 2011 revealed that infected midges were present across the country (Rasmussen et al., 2014). However, outbreaks of SBV associated diseases in ruminants have not been published, nor have cases been diagnosed during a national bovine abortion surveillance program from 2015 to 2017 (Wolf-Jäckel et al., 2020). Hence, outbreaks of SBV infection in Denmark seem to be rare, but as official surveillance for SBV is not in force in Denmark and as the infection is not notifiable, knowledge is empiric.
In adult animals, SBV induces a short-lived viremia of two to six days, associated with either none or only mild unspecific clinical signs like fever, diarrhea or reduced milk yield (Beer & Wernike, 2021; Hoffmann et al., 2012). However, SBV may cause fetal malformation, when a susceptible pregnant ruminant species becomes infected during a vulnerable phase of gestation (Beer & Wernike, 2021). Like other viruses of the Simbu serogroup such as Akabane virus (Kirkland, 2015), SBV induces a syndrome mainly characterized by brain malformation and generalized arthrogryposis (Agerholm, Hewicker-Trautwein, Peperkamp, & Windsor, 2015; Bayrou et al., 2014). Generalized arthrogryposis, usually referred to as arthrogryposis multiplex congenita (AMC), is a severe neuromuscular condition characterized by angulation and ankylosis of the joints. In addition to SBV and a few other viruses, AMC may have other causes such as genetic defects (Agerholm, McEvoy, Menzi, Jagannathan, & Drögemüller, 2016). In Denmark, a nationwide surveillance system for bovine genetic diseases has been in force since 1989. As part of this program, selected cases of congenital malformations are submitted to the University of Copenhagen for necropsy and genetic assessment. In April-May 2021, seven AMC cases were reported by veterinary practitioners and acquired for necropsy. To rule out a viral etiology, these cases were examined for teratogenic viruses and found to be positive for SBV or anti-SBV antibodies. The results of this investigation are reported here.