Viral Hemorrhagic Fevers: Disease Modeling and Transmission

National Institute Of Allergy And Infectious Diseases

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Abstract

During FY23 the focus of DMTs work was on filoviruses and orthonairoviruses. Filoviruses: Infections with ebolaviruses and marburgviruses, family Filoviridae, cause Ebola (EVD) and Marburg virus disease (MVD), respectively, with high case fatality rates. In addition, there are other filovirus genera, such as cuevaviruses, that have not been associated with human infections and disease. The natural reservoirs for filoviruses are likely different bat species. Filovirus are enveloped, non-segmented, negative-stranded RNA viruses expressing seven structural proteins. Some filoviruses, but not all, express nonstructural glycoproteins through RNA editing of the glycoprotein gene. The West African EVD outbreak has led to the licensure of vaccines treatments making EVD a success story in the field of neglected tropical diseases. (Marzi and Feldmann, J Infect Dis 2023) RNA editing has been discovered as an essential mechanism for the transcription of the glycoprotein (GP) gene of Ebola virus (EBOV). We developed a rapid transcript quantification assay (RTQA) to analyze RNA transcripts generated through RNA editing. RTQA successfully quantified the two major GP gene transcripts during infection with representative members of five ebolavirus species. Immunoblotting verified expression of the soluble (sGP) and the transmembrane GP. Our results defined RNA editing as a general trait of ebolaviruses. (Mehedi et al., J Infect Dis 2023) "Post-Ebola Syndrome" has first been described during and after the West African Ebola outbreak. In one of our studies a rhesus macaque developed neurological signs and acute respiratory distress following recovery of an Ebola virus (EBOV) infection requiring euthanasia. Interestingly, the organ tropism had changed with high virus titers in lungs, brain, eye, and reproductive organs but no virus in liver, spleen and adrenal glands, the typical target organs for acute EBOV infection. Thus, we have described an atypical EBOV disease similar to Post-Ebola Syndrome. It remains to be seen if the syndrome could be modeled and studied in future. (Marzi et al., J Infect Dis 2023) The focus of filovirus work during FY23 was on VSV-vectored filovirus vaccines. We generated and characterized VSV- SUDV and evaluated the protective efficacy following a single-dose vaccination against lethal SUDV infection in cynomolgus macaques. As we repurposed macaques from a successful previous VSV-Ebola virus (EBOV) vaccine efficacy study, we also investigated VSV-EBOV's cross-protective potential against SUDV challenge. Of the six NHPs given VSV-SUDV, none showed any signs of disease in response to the challenge. Four of the five NHPs in the control group developed characteristic clinical signs of SUDV diseases. Although the NHPs developed cross-reactive humoral responses to SUDV after VSV-EBOV vaccination and EBOV challenge, there was little cross-protection. These data emphasize the need for species-specific vaccines for ebolaviruses. Although previous VSV-EBOV immunity is boosted through VSV-SUDV vaccination, it has only limited effect on the immunogenicity and protective efficacy of VSV-SUDV. This study presented a milestone study informing public health during the SUDV outbreak in Uganda. Marzi et al, Lancet Microbe 2023 Ebola virus (EBOV) and Marburg virus (MARV) have overlapping endemicity areas. We used macaques previously vaccinated with VSV-MARV and protected against MARV challenge. After a resting period of 9 months, macaques were re-vaccinated with VSV-EBOV and challenged with EBOV resulting in 75% survival. Surviving NHPs developed EBOV GP-specific antibody titers and no viremia or clinical signs. This study again demonstrates that VSVG-based filovirus vaccine can be successfully used in individuals with pre-existing VSV vector immunity highlighting the platform's applicability for consecutive outbreak response. (Marzi et al., J Infect Dis 2023) VSV-EBOV has been successfully used in ring vaccination approaches during Ebola disease outbreaks demonstrating its general benefit in short-term prophylactic vaccination, but actual proof of its benefit in true post-exposure prophylaxis (PEP) for humans is missing. Animal studies have indicated PEP efficacy when VSV-EBOV was used within hours of lethal EBOV challenge. Here, we used a lower EBOV challenge dose and a combined intravenous and intramuscular VSV-EBOV administration to improve PEP efficacy in the rhesus macaque model. VSV-EBOV treatment 1 hour post EBOV challenge resulted in delayed disease progression but little benefit in outcome. Thus, we could not confirm previous results indicating questionable benefit of VSV-EBOV for EBOV PEP even in a nonhuman primate model. (Bushmaker et al., J Infect Dis 2023) Although significant progress has been made in the development of therapeutics against EBOV, we sought to expand upon existing strategies and combine an RNAi-based intervention with the approved VSV-EBOV vaccine to conjointly treat and vaccinate patients during an outbreak. We constructed VSV-EBOV vectors expressing artificial miRNAs (amiRNAs) targeting sequences of EBOV proteins. In vitro experiments demonstrated a robust decrease in EBOV replication using a minigenome system and infectious virus. For in vivo evaluation, MA-EBOV-infected CD-1 mice were treated 24 hours after infection with a single dose of the VSV-EBOV-amiRNA constructs. We observed no difference in disease progression or survival compared to the control-treated mice. In summary, while amiRNAs decrease viral replication in vitro, the effect is not sufficient to protect mice from lethal disease, and this therapeutic approach requires further optimization. (ODonnell et al., J Infect Dis 2023) Orthonairoviruses Introduction: Crimean-Congo hemorrhagic fever virus (CCHFV) is a tri-segmented, negative sense virus in the Bunyavirales order. The principal vector and reservoir are ticks of the Hyalomma genus and the wide geographic distribution of CCHFV follows the geographic range of these ticks. The primary routes of exposure are tick-bites and handling of infected livestock, although human-to-human spread is reported. Clinically, CCHF presents initially as a non-specific febrile illness that can rapidly progress to a severe, sometimes fatal hemorrhagic disease. The host and viral determinants of CCHFV pathogenesis are poorly understood and there are no approved vaccines or antivirals. (Hawman and Feldmann, Nat Rev Microbiol 2023) We have previously reported significant efficacy of a three-dose DNA-based vaccination regimen for CCHFV in cynomolgus macaques (Hawman et al., Nat Microbiol 2021). Here, we show that in macaques, plasmid expressed CCHFV nucleoprotein (NP) and glycoprotein precursor (GPC) antigens elicit primarily humoral and cellular immunity, respectively. We found that a two-dose vaccination regimen with plasmids expressing the NP and GPC provides significant protection against CCHFV infection. Studies investigating vaccinations with either antigen alone showed that plasmid-expressed NP could also confer protection. Our data show that this vaccine confers robust protection against CCHFV. (Hawman et al., Mol Ther 2023) We evaluated an alphavirus-based replicon RNA vaccine expressing either the CCHFV NP or GPC in a heterologous lethal mouse model. Vaccination with the RNA expressing NP alone could confer complete protection against clinical disease, but vaccination with a combination of both the NP and GPC afforded robust protection against disease and viral replication. This vaccine conferred robust protection against CCHFV and supports continued development of this vaccine. (Leventhal et al., EBioMedicine 2022)