Rift Valley fever (RVF) is an emerging zoonosis of major public health concern in Africa and Arabia. Previous outbreaks attributed camelids a significant role in the epidemiology of Rift Valley fever virus (RVFV), making them an important target species for vaccination. Using three alpacas as model-organisms for dromedary camels, the safety, immunogenicity and pathogenicity of the MP-12 vaccine were evaluated inthis study. To compare both acute and subacute effects, animals were euthanized at 3 and 31days post infection (dpi). Clinical monitoring, analysis of liver enzymes and hematological parameters demonstrated the tolerability of the vaccine, as no significant adverse effects were observed. Comprehensive analysis of serological parameters illustrated the immunogenicity of the vaccine, eliciting high neutralizing antibody titers and antibodies targeting different viral antigens. RVFV was detected in serum and liver of the alpaca euthanized 3dpi, whereas no viruswas detectable at 31dpi. Viral replication was confirmed by detection of various RVFV-antigens in hepatocytes by immunohistochemistry and the presence of mild multifocal necrotizing hepatitis. In conclusion, results indicate that MP-12 is a promising vaccine candidate but still has a residual pathogenicity, which requires further investigation.
Antibodies specific for Rift Valley fever virus (RVFV) can be detected by diverse methods, including ezyme-linked immunosortbent assay (ELISA) and virus neutralization test (VNT). The VNT is superior in sensitivity and specificity and is therefore considered the gold standard serological assay. Classical VNTs make use of virulent RVFV and therefore have to be performed in biosafety level 3 laboratories. Here, we report the development of a novel VNT that is based on an avirulent RVFV expressing the enhanced green fluorescent protein (eGFP), which can be performed safely outside level 3 biocontainment facilities. Evaluation with a broad panel of experimental sera and field sera demonstrated that this novel VNT is faster and more sensitive than the classical VNT.
Orthobunyaviruses are enveloped viruses that can cause human and animal diseases. A novel and major member is the Schmallenberg virus(SBV), the etiological agent of an emerging disease of ruminants that has been spreading all over Europe since 2011. The glycoproteins Gn and Gc of orthobunyaviruses mediate the viral entry, and specifically Gc is a major target for the humoral immune response. For example, the N terminal subdomain of the SBV glycoprotein Gc is targeted by neutralizing monoclonal antibodies that recognize conformational epitopes. Here, we determined the structural features of the N terminus of Gc, and analysed its interaction with monoclonal antibodies. We were able to demonstrate that one of two N-glycosylation sites is essential for secretion and interaction with a subset of Gc-specific monoclonal antibodies. Furthermore, four disulfide bonds (S-S) were identified and the deletion of the third S-S blocked reactivity with another subset of mAbs with virus-neutralizing and non-neutralizing activity. The mutagenesis of the N-glycosylation sites and the disulfide bonds strongly indicated the independent folding of two subdomains within the SBV Gc N terminus. Further, the epitopes recognized by a panel of mAbs could be grouped into two clusters, as revealed by fine mapping using chimeric proteins. Combining the disulfide bonding and epitope mapping allowed us to generate a structural model of the SBV Gc N-terminus. This novel information about the role and structure of the amino terminal region of SBV Gc is of general relevance for the design of antivirals and vaccines against this virus.