Jeroen Kortekaas

Creation of a Nonspreading Rift Valley Fever Virus

ABSTRACT Rift Valley fever virus (RVFV) is a mosquito-borne zoonotic bunyavirus of the genus Phlebovirus and a serious human and veterinary pathogen. RVFV contains a three-segmented RNA genome, which is comprised of the large (L), medium (M), and small (S) segments. The proteins that are essential for genome replication are encoded by the L and S segments, whereas the structural glycoproteins are encoded by the M segment. We have produced BHK replicon cell lines (BHK-Rep) that maintain replicating L and S genome segments. Transfection of BHK-Rep cells with a plasmid encoding the structural glycoproteins results in the efficient production of RVFV replicon particles (RRPs). To facilitate monitoring of infection, the NSs gene was replaced with an enhanced green fluorescent protein gene. RRPs are infectious for both mammalian and insect cells but are incapable of autonomous spreading, rendering their application outside biosafety containment completely safe. We demonstrate that a single intramuscular vaccination with RRPs protects mice from a lethal dose of RVFV and show that RRPs can be used for rapid virus neutralization tests that do not require biocontainment facilities. The methods reported here will greatly facilitate vaccine and drug development as well as fundamental studies on RVFV biology. Moreover, it may be possible to develop similar systems for other members of the bunyavirus family as well.

Rift Valley fever virus subunit vaccines confer complete protection against a lethal virus challenge

Rift Valley fever virus (RVFV) is an emerging mosquito-borne virus causing significant morbidity and mortality in livestock and humans. Rift Valley fever is endemic in Africa, but also outside this continent outbreaks have been reported. Here we report the evaluation of two vaccine candidates based on the viral Gn and Gc envelope glycoproteins, both produced in a Drosophila insect cell expression system. Virus-like particles (VLPs) were generated by merely expressing the Gn and Gc glycoproteins. In addition, a soluble form of the Gn ectodomain was expressed and affinity-purified from the insect cell culture supernatant. Both vaccine candidates fully protected mice from a lethal challenge with RVFV. Importantly, absence of the nucleocapsid protein in either vaccine candidate facilitates the differentiation between infected and vaccinated animals using a commercial recombinant nucleocapsid protein-based indirect ELISA.

Rift Valley fever virus immunity provided by a paramyxovirus vaccine vector.

Rift Valley fever virus (RVFV) causes recurrent large outbreaks among humans and livestock. Although the virus is currently confined to the African continent and the Arabian Peninsula, there is a growing concern for RVFV incursions into countries with immunologically naïve populations. The RVFV structural glycoproteins Gn and Gc are preferred targets in the development of subunit vaccines that can be used to control future outbreaks. We here report the production of Gn and Gc by a recombinant vaccine strain of the avian paramyxovirus Newcastle disease virus (NDV) and demonstrate that intramuscular vaccination with this experimental NDV-based vector vaccine provides complete protection in mice. We also demonstrate that a single intramuscular vaccination of lambs, the main target species of RVFV, is sufficient to elicit a neutralizing antibody response.

Efficacy of three candidate Rift Valley fever vaccines in sheep

Rift Valley fever virus (RVFV) is a mosquito-transmitted Bunyavirus that causes high morbidity and mortality among ruminants and humans. The virus is endemic to the African continent and the Arabian Peninsula and continues to spread into new areas. The explosive nature of RVF outbreaks requires that vaccines provide swift protection after a single vaccination. We recently developed several candidate vaccines and here report their efficacy in lambs within three weeks after a single vaccination. The first vaccine comprises the purified ectodomain of the Gn structural glycoprotein formulated in a water-in-oil adjuvant. The second vaccine is based on a Newcastle disease virus-based vector that produces both RVFV structural glycoproteins Gn and Gc. The third vaccine comprises a recently developed nonspreading RVFV. The latter two vaccines were administered without adjuvant. The inactivated whole virus-based vaccine produced by Onderstepoort Biological Products was used as a positive control. Five out of six mock-vaccinated lambs developed high viremia and fever and one lamb succumbed to the challenge infection. A single vaccination with each vaccine resulted in a neutralizing antibody response within three weeks after vaccination and protected lambs from viremia, pyrexia and mortality.

Neurotropic virus infections as the cause of immediate and delayed neuropathology

A wide range of viruses from different virus families in different geographical areas, may cause immediate or delayed neuropathological changes and neurological manifestations in humans and animals. Infection by neurotropic viruses as well as the resulting immune response can irreversibly disrupt the complex structural and functional architecture of the central nervous system, frequently leaving the patient or affected animal with a poor or fatal prognosis. Mechanisms that govern neuropathogenesis and immunopathogenesis of viral infections are highlighted, using examples of well-studied virus infections that are associated with these alterations in different populations throughout the world. A better understanding of the molecular, epidemiological and biological characteristics of these infections and in particular of mechanisms that underlie their clinical manifestations may be expected to provide tools for the development of more effective intervention strategies and treatment regimens.

Heparan sulfate facilitates Rift Valley fever virus entry into the cell

ABSTRACT Rift Valley fever virus (RVFV), an emerging arthropod-borne pathogen, has a broad host and cell tropism. Here we report that the glycosaminoglycan heparan sulfate, abundantly present on the surface of most animal cells, is required for efficient entry of RVFV. Entry was significantly reduced by preincubating the virus inoculum with highly sulfated heparin, by enzymatic removal of heparan sulfate from cells and in cells genetically deficient in heparan sulfate synthesis.

One health approach to Rift Valley fever vaccine development

Since its discovery in the 1930s, Rift Valley fever virus (RVFV) spread across the African continent and invaded the Arabian Peninsula and several islands off the coast of Southeast Africa. The virus causes recurrent outbreaks in these regions, and its continued spread is of global concern. Next-generation veterinary vaccines of improved efficacy and safety are being developed that can soon be used for the widespread vaccination of livestock. However, due to regulatory and economic challenges, vaccine manufacturers have been reluctant to develop a human vaccine. Recent innovations in veterinary vaccinology, animal models and licensing strategies can now be used to overcome these hurdles. This paper reviews the historical impact of RVFV on human health and proposes strategies to develop and license a next-generation vaccine for both animals and humans.

Acid-activated structural reorganization of the Rift Valley fever virus Gc fusion protein

ABSTRACT The entry of the enveloped Rift Valley fever virus (RVFV) into its host cell is mediated by the viral glycoproteins Gn and Gc. We investigated the RVFV entry process and, in particular, its pH-dependent activation mechanism using our recently developed nonspreading-RVFV-particle system. Entry of the virus into the host cell was efficiently inhibited by lysosomotropic agents that prevent endosomal acidification and by compounds that interfere with dynamin- and clathrin-dependent endocytosis. Exposure of plasma membrane-bound virions to an acidic pH (<pH 6) equivalent to the pH of late endolysosomal compartments allowed the virus to bypass the endosomal route of infection. Acid exposure of virions in the absence of target membranes triggered the class II-like Gc fusion protein to form extremely stable oligomers that were resistant to SDS and temperature dissociation and concomitantly compromised virus infectivity. By targeted mutagenesis of conserved histidines in Gn and Gc, we demonstrated that mutation of a single histidine (H857) in Gc completely abrogated virus entry, as well as acid-induced Gc oligomerization. In conclusion, our data suggest that after endocytic uptake, RVFV traffics to the acidic late endolysosomal compartments, where histidine protonation drives the reorganization of the Gc fusion protein that leads to membrane fusion.

Intramuscular inoculation of calves with an experimental Newcastle disease virus-based vector vaccine elicits neutralizing antibodies against Rift Valley fever virus

In the past decade, the use of Newcastle disease virus (NDV) as a vaccine vector for the prevention of economically important livestock diseases as well as for human diseases has been extensively explored. In this study, we have constructed a recombinant NDV vaccine virus, named NDFL-Gn, that produces the Rift Valley fever virus (RVFV) Gn glycoprotein. Calves were immunized via either the intranasal route or the intramuscular route. Delivery via the intranasal route elicited no detectable antibody responses, whereas delivery via the intramuscular route elicited antibodies against both NDV and the Gn protein. The RVFV-neutralizing activity of the antisera from intramuscularly vaccinated calves was demonstrated, suggesting that NDV is a promising vaccine vector for the prevention of RVF in calves.

Rift Valley Fever Vaccine Development, Progress and Constraints

The workshop Rift Valley Fever Vaccine Development, Progress and Constraints was organized by the Food and Agriculture Organization of the United Nations (FAO) and the Central Veterinary Institute of Wageningen University and Research Centre, under the umbrella of the Global Framework for the Progressive Control of Transboundary Animal Diseases, a joint initiative of FAO and the World Organisation for Animal Health. The workshop was supported by the Netherlands Ministry of Economic Affairs, Agriculture and Innovation, and by the US Centers for Disease Control and Prevention; other participants included the World Health Organization and the International Atomic Energy Agency. The meeting occurred January 19–21, 2011, at FAO headquarters in Rome, Italy, and was attended by 34 leading scientists in Rift Valley fever virus (RVFV) vaccine development, representatives of international organizations, and policy makers. Stakeholders from industry were represented by the International Federation for Animal Health. The main objective of the meeting was to gain consensus about desired characteristics of novel veterinary RVFV vaccines and to discuss how incentives can be established to ensure that these vaccines come to market.