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.