High genetic variability of Schmallenberg virus M-segment leads to efficient immune escape from neutralizing antibodies

Identification of a broadly neutralizing epitope within Gc protein of Akabane virus using newly prepared neutralizing monoclonal antibodies

Akabane virus (AKAV) is characterized by abortion, stillbirth, premature birth, and congenital deformities in livestock and is widely distributed throughout Australia, Southeast Asia, East Asia, the Middle East, and Africa. Gc protein is the major neutralizing target of AKAV and is often considered as an immunogen to prepare neutralizing antibodies. In this study, we prepared and characterized three monoclonal antibodies (mAbs), 4D1, 4E6, and 4F12, against the Gc protein of AKAV (TJ2016 strain). Western blot (WB) and indirect immunofluorescence assay (IFA) analysis proved that the mAbs can react with both the truncated recombinant AKAV Gc protein and the natural Gc protein produced in the AKAV-infected cells. Further research demonstrated that these mAbs possess neutralizing activity. We next defined a neutralizing epitope 1134SVQSFDGKL1142 by screening a panel of overlapping peptides spanning the truncated Gc protein (aa991∼1232) using the generated neutralizing mAbs. Bioinformatic analysis shows that the neutralizing epitope is highly conserved across different genotypes of AKAV. The newly produced neutralizing mAbs and the identified neutralizing epitope in this study enrich the antigenic epitope information of the AKAV Gc protein and could have potential applications in the development of antigen and antibody detection systems that are specific to AKAV.

Characterization of a natural 'dead-end' variant of Schmallenberg virus

Schmallenberg virus (SBV) belongs to the Simbu serogroup within the family Peribunyaviridae, genus Orthobunyavirus and is transmitted by Culicoides biting midges. Infection of naïve ruminants in a critical phase of gestation may lead to severe congenital malformations. Sequence analysis from viremic animals revealed a very high genome stability. In contrast, sequence variations are frequently described for SBV from malformed fetuses. In addition to S segment mutations, especially within the M segment encoding the major immunogen Gc, point mutations or genomic deletions are also observed. Analysis of the SBV_D281/12 isolate from a malformed fetus revealed multiple point mutations in all three genome segments. It also has a large genomic deletion in the antigenic domain encoded by the M segment compared to the original SBV reference strain 'BH80/11' isolated from viremic blood in 2011. Interestingly, SBV_D281/12 showed a marked replication deficiency in vitro in Culicoides sonorensis cells (KC cells), but not in standard baby hamster kidney cells (BHK-21). We therefore generated a set of chimeric viruses of rSBV_D281/12 and wild-type rSBV_BH80/11 by reverse genetics, which were characterized in both KC and BHK-21 cells. It could be shown that the S segment of SBV_D281/12 is responsible for the replication deficit and that it acts independently from the large deletion within Gc. In addition, a single point mutation at position 111 (S to N) of the nucleoprotein was identified as the critical mutation. Our results suggest that virus variants found in malformed fetuses and carrying characteristic genomic mutations may have a clear 'loss of fitness' for their insect hosts in vitro. It can also be concluded that such mutations lead to virus variants that are no longer part of the natural transmission cycle between mammalian and insect hosts. Interestingly, analysis of a series of SBV sequences confirmed the S111N mutation exclusively in samples of malformed fetuses and not in blood from viremic animals. The characterization of these changes will allow the definition of protein functions that are critical for only one group of hosts.

Failure to detect Schmallenberg virus RNA in ram semen in the UK (2016-2018)

Background

Schmallenberg virus (SBV) is a midge-borne arbovirus that first emerged in the European ruminant population in 2011 and has since settled to an endemic pattern of disease outbreaks on an approximately 4-year cycle when herd immunity from the previous circulation drops to a point allowing renewed widescale virus circulation. The impacts of trade restrictions on genetic products (semen, embryos) from affected areas were severe, particularly after the discovery that the virus is intermittently shed in the semen of a small number of bulls. The trade in small ruminant (ram and goat) semen is less than that of bulls; nonetheless, there has been no study into the shedding rate of SBV in ram semen.

Methods

Semen samples (n = 65) were collected as part of UK ram trials and artificial insemination studies around the period of the 2016-2018 SBV recirculation. Semen was preserved in RNAlater for shipping, and RNA extraction with RNeasy and S gene RT-quantitative PCR performed for SBV nucleic acid detection.

Results

No SBV RNA was detected in any samples.

Conclusions

While larger numbers of animals would be needed to completely exclude the possibility of SBV shedding in ram semen, this trial nonetheless highlights that this is likely a rare event if it occurs at all and is unlikely to play a role in disease transmission.

Identification and Genetic Characterization of Viral Pathogens in Ruminant Gestation Abnormalities, Israel, 2015-2019

Infectious agents including viruses are important abortifacients and can cause fetal abnormalities in livestock animals. Here, samples that had been collected in Israel from aborted or malformed ruminant fetuses between 2015 and 2019 were investigated for the presence of the following viruses: the reoviruses bluetongue virus (BTV) and epizootic hemorrhagic disease virus (EHDV), the flaviviruses bovine viral diarrhea virus (BVDV) and border disease virus (BDV), the peribunyaviruses Shuni virus (SHUV) and Akabane virus (AKAV), bovine herpesvirus type 1 (BoHV-1) and bovine ephemeral fever virus (BEFV). Domestic (cattle, sheep, goat) and wild/zoo ruminants were included in the study. The presence of viral nucleic acid or antigen could be confirmed in 21.8 % of abnormal pregnancies (213 out of 976 investigated cases), with peribunyaviruses, reoviruses and pestiviruses being the most prevalent. At least four different BTV serotypes were involved in abnormal courses of pregnancy in Israel. The subtyping of pestiviruses revealed the presence of two BDV and several distinct BVDV type 1 strains. The peribunyaviruses AKAV and SHUV were identified annually throughout the study period, however, variation in the extent of virus circulation could be observed between the years. In 2018, AKAV even represented the most detected pathogen in cases of small domestic ruminant gestation abnormalities. In conclusion, it was shown that various viruses are involved in abnormal courses of pregnancy in ruminants in Israel.