Genetic stability of Schmallenberg virus in vivo during an epidemic, and in vitro, when passaged in the highly susceptible porcine SK-6 cell line

Abstract

Schmallenberg virus (SBV), an arthropod-borne orthobunyavirus was first detected in 2011 in cattle suffering from diarrhea and fever. The most severe impact of an SBV infection is the induction of malformations in newborns and abortions. Between 2011 and 2013 SBV spread throughout Europe in an unprecedented epidemic wave. SBV contains a tripartite genome consisting of the three negative-sense RNA segments L, M, and S. The virus is usually isolated from clinical samples by inoculation of KC (insect) or BHK-21 (mammalian) cells. Several virus passages are required to allow adaptation of SBV to cells in vitro. In the present study, the porcine SK-6 cell line was used for isolation and passaging of SBV. SK-6 cells proved to be more sensitive to SBV infection and allowed to produce higher titers more rapidly as in BHK-21 cells after just one passage. No adaptation was required. In order to determine the in vivo genetic stability of SBV during an epidemic spread of the virus the nucleotide sequence of the genome from seven SBV field isolates collected in summer 2012 in Switzerland was determined and compared to other SBV sequences available in GenBank. A total of 101 mutations, mostly transitions randomly dispersed along the L and M segment were found when the Swiss isolates were compared to the first SBV isolated late 2011 in Germany. However, when these mutations were studied in detail, a previously described hypervariable region in the M segment was identified. The S segment was completely conserved among all sequenced SBV isolates. To assess the in vitro genetic stability of SBV, three isolates were passage 10 times in SK-6 cells and sequenced before and after passaging. Between two and five nt exchanges per genome were found. This low in vitro mutation rate further demonstrates the suitability of SK-6 cells for SBV propagation.

Re‐emergence of the Schmallenberg virus associated triad hydranencephaly‐micromyelia‐arthrogryposis in a newborn calf in Belgium, 2016

“…As this calf comprehensively recapitulated the gross alterations the authors had specifically associated with natural in utero infection by SBV (Bayrou and others 2014), the presence of the SBV genome was first sought by (RT)-qPCR (Bilk and others 2012, Hofmann and others 2015). The presence of segments S and L genomic RNA was ascertained in the brainstem (BS) and SC, with Ct values ranging from 31.9±0.26 (BS) to 35.4±0.52 (SC) and from 35.2±0.42 (BS) to 37.6±0.42 (SC) for the S and L segments, respectively.…”

Schmallenberg virus: a systematic international literature review (2011-2019) from an Irish perspective

“…This is supported by reports of high SBV genetic stability in vector-derived SBV sequences in Poland [44]. Additionally, Hoffmann et al (2015) reported that SBV has a relatively low mutation rate both in vitro and in vivo [45]. Several field studies of virus variability have also demonstrated that the virus is relatively stable over time [46, 47].…”

Sequence analysis of Schmallenberg virus genomes detected in Hungary

“…To date, 11 full SBV genomic sequences were available in GenBank, originating from Germany, the Netherlands, and Belgium [3,12,[27][28][29]. To investigate the variability of the SBV sequences, we characterized the coding sequence of seven SBV strains collected in Hungary, including the virus from the first local case detected in 2012 (SBV-Hun4), and six additional strains from samples collected in 2014.…”