Lassa virus (LASV) is endemic in Western Africa and is estimated to infect hundreds of thousands of individuals annually. A considerable number of these infections result in Lassa fever (LF), which is associated with significant morbidity and a case-fatality rate as high as 69% among hospitalized confirmed patients. U.S. Food and Drug Administration-approved LF vaccines are not available. Current antiviral treatment is limited to off-label use of a nucleoside analogue, ribavirin, that is only partially effective and associated with significant side effects. We generated and characterized a recombinant LASV expressing a codon-deoptimized (CD) glycoprotein precursor gene (GPC), rLASV-GPC/CD. Comparison of growth kinetics and peak titers showed that rLASV-GPC/CD is slightly attenuated in cell culture compared to wild-type (WT) recombinant LASV (rLASV-WT). However, rLASV-GPC/CD is highly attenuated in strain 13 and Hartley guinea pigs, as reflected by the absence of detectable clinical signs in animals inoculated with rLASV-GPC/CD. Importantly, a single subcutaneous dose of rLASV-GPC/CD provides complete protection against an otherwise lethal exposure to LASV. Our results demonstrate the feasibility of implementing a CD approach for developing a safe and effective LASV live-attenuated vaccine candidate. Moreover, rLASV-GPC/CD might provide investigators with a tool to safely study LASV outside maximum (biosafety level 4) containment, which could accelerate the elucidation of basic aspects of the molecular and cell biology of LASV and the development of novel LASV medical countermeasures. IMPORTANCE Lassa virus (LASV) infects several hundred thousand people in Western Africa, resulting in many lethal Lassa fever (LF) cases. Licensed LF vaccines are not available, and anti-LF therapy is limited to off-label use of the nucleoside analog ribavirin with uncertain efficacy. We describe the generation of a novel live-attenuated LASV vaccine candidate. This vaccine candidate is based on mutating wild-type (WT) LASV in a key region of the viral genome, the glycoprotein precursor (GPC) gene. These mutations do not change the encoded GPC but interfere with its production in host cells. This mutated LASV (rLASV-GPC/CD) behaves like WT LASV (rLASV-WT) in cell culture, but in contrast to rLASV-WT, does not cause disease in inoculated guinea pigs. Guinea pigs immunized with rLASV-GPC/CD were protected against an otherwise lethal exposure to WT LASV. Our results support the testing of this candidate vaccine in nonhuman primate models ofLF.

Nipah virus is a highly lethal zoonotic paramyxovirus that was first recognized in Malaysia during an outbreak in 1998. During this outbreak, Nipah virus infection caused a severe febrile neurological disease in humans who worked in close contact with infected pigs. The case fatality rate in humans was approximately 40%. Since 2001, NiV has re-emerged in Bangladesh and India where fruit bats (Pteropus spp.) have been identified as the principal reservoir of the virus. Transmission to humans is considered to be bat-to-human via food contaminated with bat saliva, or consumption of contaminated raw date palm sap, although human-to-human transmission of Nipah virus has also been documented. To date, there are no approved prophylactic options or treatment for NiV infection. In this study, we produced mammalian cell-derived native Nipah virus-like particles composed of Nipah virus G, F and M proteins for use as a novel Nipah virus vaccine. Previous studies demonstrated that the virus-like particles were structurally similar to authentic virus, functionally assembled and immunoreactive. In the studies reported here, purified Nipah virus-like particles were utilized either alone or with adjuvant to vaccinate golden Syrian hamsters with either three-dose or one-dose vaccination regimens followed by virus challenge. These studies found that Nipah virus-like particle immunization of hamsters induced significant neutralizing antibody titers and provided complete protection to all vaccinated animals following either single or three-dose vaccine schedules. These studies prove the feasibility of a virus-like particle-based vaccine for protection against Nipah virus infection.

Simian hemorrhagic fever virus (SHFV) causes a severe and almost uniformly fatal viral hemorrhagic fever in Asian macaques but is thought to be nonpathogenic for humans. To date, the SHFV life cycle is almost completely uncharacterized on the molecular level. Here, we describe the first steps of the SHFV life cycle. Our experiments indicate that SHFV enters target cells by lowpH-dependent endocytosis. Dynamin inhibitors, chlorpromazine, methyl-␤-cyclodextrin, chloroquine, and concanamycin A dramatically reduced SHFV entry efficiency, whereas the macropinocytosis inhibitors EIPA, blebbistatin, and wortmannin and the caveolin-mediated endocytosis inhibitors nystatin and filipin III had no effect. Simian hemorrhagic fever virus (SHFV) is currently classified together with equine arteritis virus (EAV), lactate dehydrogenase-elevating virus (LDV), and porcine reproductive and respiratory syndrome virus (PRRSV) in the genus Arterivirus, family Arteriviridae, in the order Nidovirales (1). The four arteriviruses are serologically distinct and cause remarkably different diseases in phylogenetically distant hosts. SHFV and SHFV-like viruses infect various African nonhuman primates without causing overt disease (2-5). In Asian macaques, however, SHFV causes a viral hemorrhagic fever that is nearly 100% lethal (6, 7).Arterivirions are spherical to pleomorphic (40 to 55 nm in diameter) and enveloped and contain small surface protrusions (8). Like all arteriviruses, SHFV has a nonsegmented, linear, single-stranded RNA genome of positive polarity. The genome is polycistronic, capped at its 5= end and polyadenylated at its 3= end, and serves partially as an mRNA (9-12). Starting at the 5= end, arterivirus genomes contain two plus-sense large open reading frames (ORFs 1a and 1b) that are directly translated into polyproteins pp1a and pp1ab. These polyproteins are autocatalytically cleaved into Ͼ12 nonstructural proteins that form the viral replicase complex that is also necessary for the synthesis of mRNA transcripts of the remaining, nested set of ORFs (reviewed in references 1 and 13). Similar to those of most nidoviruses, all SHFV mRNAs are 5= and 3= coterminal in sequence with the viral genome and are produced by discontinuous RNA transcription (12). These subgenomic mRNAs encode at least eight structural proteins that are essential for virion infectivity and appear to have functional analogs in particles of other arteriviruses (E, GP2 to -5, GP5a, M, and N) (reviewed in references 1 and 13). SHFV and