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Live-attenuated Rift Valley fever (RVF) vaccines transiently replicate in the vaccinated host, thereby effectively initiating an innate and adaptive immune response. Rift Valley fever virus (RVFV)-specific neutralizing antibodies are considered the main correlate of protection. Vaccination with classical live-attenuated RVF vaccines during gestation in livestock has been associated with fetal malformations, stillbirths, and fetal demise. Facilitated by an increased understanding of the RVFV infection and replication cycle and availability of reverse genetics systems, novel rationally-designed live-attenuated candidate RVF vaccines with improved safety profiles have been developed. Several of these experimental vaccines are currently advancing beyond the proof-of-concept phase and are being evaluated for application in both animals and humans. We here provide perspectives on some of these next-generation live-attenuated RVF vaccines and highlight the opportunities and challenges of these approaches to improve global health.

Rift Valley fever virus (RVFV) (family Phenuiviridae) can cause severe disease, and outbreaks of this mosquito-borne pathogen pose a significant threat to public and animal health. Yet many molecular aspects of RVFV pathogenesis remain incompletely understood. Natural RVFV infections are acute, characterized by a rapid onset of peak viremia during the first days post-infection, followed by a rapid decline. Although in vitro studies identified a major role of interferon (IFN) responses in counteracting the infection, a comprehensive overview of the specific host factors that play a role in RVFV pathogenesis in vivo is still lacking. Here, the host in vivo transcriptional profiles in the liver and spleen tissues of lambs exposed to RVFV are studied using RNA sequencing (RNA-seq) technology. We validate that IFN-mediated pathways are robustly activated in response to infection. We also link the observed hepatocellular necrosis with severely compromised organ function, which is reflected as a marked downregulation of multiple metabolic enzymes essential for homeostasis. Furthermore, we associate the elevated basal expression of LRP1 in the liver with RVFV tissue tropism. Collectively, the results of this study deepen the knowledge of the in vivo host response during RVFV infection and reveal new insights into the gene regulation networks underlying pathogenesis in a natural host

We used RNA-seq technology to study the host in vivo transcriptional profiles in liver and spleen tissues of lambs exposed to Rift Valley fever virus., We used RNA-seq technology to study the host in vivo transcriptional profiles in liver and spleen tissues of lambs exposed to Rift Valley fever virus.

Rift Valley fever virus (RVFV) is a (re)emerging mosquito-borne pathogen impacting human and animal health. How RVFV spreads through a population depends on population-level and individual-level interactions between vector, host and pathogen. Here, we estimated the probability for RVFV to transmit to naive animals by experimentally exposing lambs to a bite of an infectious mosquito, and assessed if and how RVFV infection subsequently developed in the exposed animal. Aedes aegypti mosquitoes, previously infected via feeding on a viremic lamb, were used to expose naive lambs to the virus. Aedes aegypti colony mosquitoes were used as they are easy to maintain and readily feed in captivity. Other mosquito spp. could be examined with similar methodology. Lambs were exposed to either 1-3 (low exposure) or 7-9 (high exposure) infectious mosquitoes. All lambs in the high exposure group became viremic and showed characteristic signs of Rift Valley fever within 2-4 days post exposure. In contrast, 3 out of 12 lambs in the low exposure group developed viremia and disease, with similar peak-levels of viremia as the high exposure group but with some heterogeneity in the onset of viremia. These results suggest that the likelihood for successful infection of a ruminant host is affected by the number of infectious mosquitoes biting, but also highlights that a single bite of an infectious mosquito can result in disease. The per bite mosquito-to-host transmission efficiency was estimated at 28% (95% confidence interval: 15 - 47%). We subsequently combined this transmission efficiency with estimates for life traits of Aedes aegypti or related mosquitoes into a Ross-McDonald mathematical model to illustrate scenarios under which major RVFV outbreaks could occur in naïve populations (i.e., R0 >1). The model revealed that relatively high vector-to-host ratios as well as mosquitoes feeding preferably on competent hosts are required for R0 to exceed 1. Altogether, this study highlights the

Compared to free antigens, antigens immobilized on scaffolds, such as nanoparticles, generally show improved immunogenicity. Conventionally, antigens are conjugated to scaffolds through genetic fusion or chemical conjugation, which may result in impaired assembly or hetero-geneous binding and orientation of the antigens. By combining two emerging technologies—i.e., self-assembling multimeric protein scaffold particles (MPSPs) and bacterial superglue—these short-comings can be overcome and antigens can be bound on particles in their native conformation. In the present work, we assessed whether this technology could improve the immunogenicity of a candidate subunit vaccine against the zoonotic Rift Valley fever virus (RVFV). For this, the head domain of glycoprotein Gn, a known target of neutralizing antibodies, was coupled on various MPSPs to further assess immunogenicity and efficacy in vivo. The results showed that the Gn head domain, when bound to the lumazine synthase-based MPSP, reduced mortality in a lethal mouse model and protected lambs, the most susceptible RVFV target animals, from viremia and clinical signs after immunization. Furthermore, the same subunit coupled to two other MPSPs (Geobacillus stearothermophilus E2 or a modified KDPG Aldolase) provided full protection in lambs as well.

Emerging infectious diseases represent an increasing threat to human and animal health. Therefore, safe and effective vaccines that could be available within a short time frame after an outbreak are required for adequate prevention and control. Here, we developed a robust and versatile self-assembling multimeric protein scaffold particle (MPSP) vaccine platform using lumazine synthase (LS) from Aquifex aeolicus. This scaffold allowed the presentation of peptide epitopes by genetic fusion as well as the presentation of large antigens by bacterial superglue-based conjugation to the pre-assembled particle. Using the orthobunyavirus model Schmallenberg virus (SBV) we designed MPSPs presenting major immunogens of SBV and assessed their efficacy in a mouse model as well as in cattle, a target species of SBV. All prototype vaccines conferred protection from viral challenge infection and the multivalent presentation of the selected antigens on the MPSP markedly improved their immunogenicity compared to the monomeric subunits. Even a single shot vaccination protected about 80% of mice from an otherwise lethal dose of SBV. Most importantly, the MPSPs induced a virtually sterile immunity in cattle. Altogether, LS represents a promising platform for modular and rapid vaccine design.

Foot-and-mouth disease (FMD) vaccine efficacy is mainly determined by the content of intact virions (146S) and empty capsids (75S). Both particles may dissociate into 12S subunits upon vaccine manufacturing, formulation, and storage, reducing vaccine potency. We report the isolation of capsid-specific llama single-domain antibodies (VHHs) with broad strain recognition that can be used to quantify intact capsids in FMD vaccines by double antibody sandwich (DAS) ELISA. One capsid-specific VHH displayed remarkably broad strain reactivity, recognizing 14 strains represent-ing the 13 most important lineages of serotype A, and two VHHs cross-reacted with other serotypes. We additionally show that the newly isolated VHHs, as well as previously characterized VHHs, can be used to identify antigenic differences between authentic 146S and 75S capsids, as well as corre-sponding genetically engineered virus-like particles (VLPs). Our work underscores that VHHs are excellent tools for monitoring the quantity and stability of intact capsids during vaccine manufac-turing, formulation, and storage, and additionally shows that VHHs can be used to predict the na-tive-like structure of VLPs

Classical swine fever is a highly contagious and deadly disease in swine. The disease can be controlled effectively by vaccination with an attenuated virus known as the “Chinese” (C)-strain. A single vaccination with the C-strain provides complete protection against highly virulent isolates within days after vaccination, making it one of the most efficacious veterinary vaccines ever developed. A disadvantage of the C-strain is that vaccinated animals cannot be serologically differentiated from animals that are infected with wild-type Classical swine fever virus. Previously, a C-strain-based vaccine with a stable deletion in the E2 structural glycoprotein was developed, which allows for differentiation between infected and vaccinated animals (DIVA). The resulting vaccine, which we named C-DIVA, is compatible with a commercial E2 ELISA, modified to render it suitable as a DIVA test. In the present work, three groups of eight piglets were vaccinated with escalating doses of the C-DIVA vaccine and challenged two weeks after vaccination. One group of four unvaccinated piglets served as controls. Piglets were monitored for clinical signs until three weeks after challenge and blood samples were collected to monitor viremia, leukocyte and thrombocyte levels, and antibody responses. The presence of challenge virus RNA in oropharyngeal swabs was investigated to first gain insight into the potential of C-DIVA to prevent shedding. The results demonstrate that a single vaccination with 70 infectious virus particles of C-DIVA protects pigs from the highly virulent Brescia strain.

Shuni virus (SHUV) is a neglected teratogenic and neurotropic orthobunyavirus that was discovered in the 1960s in Nigeria and was subsequently detected in South Africa, Zimbabwe, and Israel. The virus was isolated from field-collected biting midges and mosquitoes and shown to disseminate efficiently in laboratory-reared biting midges, suggesting that members of the families Culicidae and Ceratopogonidae may function as vectors. SHUV infections have been associated with severe neurological disease in horses, a variety of wildlife species, and domesticated ruminants. SHUV infection of ruminants is additionally associated with abortion, stillbirth, and congenital malformations. The detection of antibodies in human sera also suggests that the virus may have zoonotic potential. To understand how SHUV crosses the ruminant placenta, we here infected pregnant ewes and subsequently performed detailed clinical-and histopathological examination of placental tissue. We found that SHUV targets both maternal epithelial cells and fetal trophoblasts, that together form the maternal-fetal interface of the ovine placenta. Experiments with human placental explants, furthermore, revealed replication of SHUV in syncytiotrophoblasts, which are generally highly resistant to virus infections. Our findings provide novel insights into vertical transmission of SHUV in sheep and call for research on the potential risk of SHUV infection during human pregnancies.