Work with infectious Ebola viruses is restricted to biosafety level 4 (BSL4) laboratories, presenting a significant barrier for studying these viruses. Life cycle modeling systems, including minigenome systems and transcription-and replication-competent virus-like particle (trVLP) systems, allow modeling of the virus life cycle under BSL2 conditions; however, all current systems model only certain aspects of the virus life cycle, rely on plasmid-based viral protein expression, and have been used to model only single infectious cycles. We have developed a novel life cycle modeling system allowing continuous passaging of infectious trVLPs containing a tetracistronic minigenome that encodes a reporter and the viral proteins VP40, VP24, and GP 1,2 . This system is ideally suited for studying morphogenesis, budding, and entry, in addition to genome replication and transcription. Importantly, the specific infectivity of trVLPs in this system was ϳ500-fold higher than that in previous systems. Using this system for functional studies of VP24, we showed that, contrary to previous reports, VP24 only very modestly inhibits genome replication and transcription when expressed in a regulated fashion, which we confirmed using infectious Ebola viruses. Interestingly, we also discovered a genome length-dependent effect of VP24 on particle infectivity, which was previously undetected due to the short length of monocistronic minigenomes and which is due at least partially to a previously unknown function of VP24 in RNA packaging. Based on our findings, we propose a model for the function of VP24 that reconciles all currently available data regarding the role of VP24 in nucleocapsid assembly as well as genome replication and transcription. IMPORTANCEEbola viruses cause severe hemorrhagic fevers in humans, with no countermeasures currently being available, and must be studied in maximum-containment laboratories. Only a few of these laboratories exist worldwide, limiting our ability to study Ebola viruses and develop countermeasures. Here we report the development of a novel reverse genetics-based system that allows the study of Ebola viruses without maximum-containment laboratories. We used this system to investigate the Ebola virus protein VP24, showing that, contrary to previous reports, it only modestly inhibits virus genome replication and transcription but is important for packaging of genomes into virus particles, which constitutes a previously unknown function of VP24 and a potential antiviral target. We further propose a comprehensive model for the function of VP24 in nucleocapsid assembly. Importantly, on the basis of this approach, it should easily be possible to develop similar experimental systems for other viruses that are currently restricted to maximum-containment laboratories. E bola virus is a negative-sense RNA virus (NSV) and the causative agent of a severe hemorrhagic fever in humans and nonhuman primates, with case fatality rates being up to 90% (1). The VP24 protein is unique to filoviruses and has no ...

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Widespread circulation of SARS-CoV-2 in humans raises the theoretical risk of reverse zoonosis events with wildlife, reintroductions of SARS-CoV-2 into permissive nondomesticated animals. Here we report that North American deer mice (Peromyscus maniculatus) are susceptible to SARS-CoV-2 infection following intranasal exposure to a human isolate, resulting in viral replication in the upper and lower respiratory tract with little or no signs of disease. Further, shed infectious virus is detectable in nasal washes, oropharyngeal and rectal swabs, and viral RNA is detectable in feces and occasionally urine. We further show that deer mice are capable of transmitting SARS-CoV-2 to naïve deer mice through direct contact. The extent to which these observations may translate to wild deer mouse populations remains unclear, and the risk of reverse zoonosis and/or the potential for the establishment of Peromyscus rodents as a North American reservoir for SARS-CoV-2 remains unknown.

SUMMARY Recent and ongoing outbreaks of Ebola virus disease (EVD) underscore the unpredictable nature of ebolavirus reemergence and the urgent need for antiviral treatments. Unfortunately, available experimental vaccines and immunotherapeutics are specific for a single member of the Ebolavirus genus, Ebola virus (EBOV), and ineffective against other ebolaviruses associated with EVD, including Sudan virus (SUDV) and Bundibugyo virus (BDBV). Here we show that MBP134AF, a pan-ebolavirus therapeutic comprising two broadly neutralizing human antibodies (bNAbs), affords unprecedented effectiveness and potency as a therapeutic countermeasure to antigenically diverse ebolaviruses. MBP134AF could fully protect ferrets against lethal EBOV, SUDV, and BDBV infection, and a single 25-mg/kg dose was sufficient to protect NHPs against all three viruses. The development of MBP134AF provides a successful model for the rapid discovery and translational advancement of immunotherapeutics targeting emerging infectious diseases.