Discussion
Bovine fetuses are expected to be vulnerable to the teratogenic properties of SBV from about 30 to 150 days of gestation (König et al., 2019; Wernike, Holsteg, Schirrmeier, Hoffmann, & Beer, 2014). By using the recorded insemination date or by backwards calculation from the calving dates, the fetuses presented in this study were probably exposed to SBV from early August 2020 and during the late summer and autumn. Five out of the six cases were born within a 14 days period and all cases were found within a narrow geographic region of the Jutlandic peninsula (Figure 3). This indicates the occurrence of a local unnoticed emergence of SBV during a short period in late summer or autumn of 2020. In Central Europe, SBV has established an endemic status with cyclic re-occurrence every two to three years (Larska, 2018; Wernike & Beer, 2017, 2020), but also resurgence of SBV in a given area after longer periods of epidemiological silence has been reported previously (Bayrou et al., 2021; Delooz et al., 2017). SBV was detected in Denmark in 2011 for the first time (Rasmussen et al., 2014) and although the knowledge on SBV infection of domestic ruminants in this country is sparse, it is likely that the reported cases represent such a resurgence of the virus.
The observed malformations as well as the significantly reduced body weight are similar to SBV-induced alterations reported previously in infected bovine fetuses (Bayrou et al., 2014; Herder, Wohlsein, Peters, Hansmann, & Baumgartner, 2012; Peperkamp et al., 2012).
An initial recognition of AMC with post mortem findings of brain malformations like hydrocephalus and cerebellar dysplasia should lead to a presumptive etiological diagnosis of fetal SBV exposure, which is to be verified by laboratory diagnostics. SBV is usually associated with severe dystocia in cattle urging for either delivery by fetotomy or Cesarean section. Bovine practitioners are therefore first line personnel in recognition of spread of SBV and other teratogenic viruses in cattle and surveillance systems should be in place to allow proper laboratory investigation of such cases. In the present Danish cases, the malformed calves were submitted as part of the national surveillance of bovine genetic diseases and examined for SBV exposure as part of the diagnostic workout.
Ethics Statement: The authors confirm that the ethical policies of the journal, as noted on the journal’s author guidelines page, have been adhered to. The fetuses and clinical specimens were submitted in the context of a Danish nationwide surveillance system for bovine genetic diseases, no further permissions were necessary.
Conflict of Interest: None.
Data Availability Statement: The data that support the findings of this study are available from the corresponding author upon reasonable request.