The Ferret as a Model for Filovirus Pathogenesis and Countermeasure Evaluation

Non-Ebola Filoviruses: Potential Threats to Global Health Security

Filoviruses are negative-sense single-stranded RNA viruses often associated with severe and highly lethal hemorrhagic fever in humans and nonhuman primates, with case fatality rates as high as 90%. Of the known filoviruses, Ebola virus (EBOV), the prototype of the genus Orthoebolavirus, has been a major public health concern as it frequently causes outbreaks and was associated with an unprecedented outbreak in several Western African countries in 2013-2016, affecting 28,610 people, 11,308 of whom died. Thereafter, filovirus research mostly focused on EBOV, paying less attention to other equally deadly orthoebolaviruses (Sudan, Bundibugyo, and Taï Forest viruses) and orthomarburgviruses (Marburg and Ravn viruses). Some of these filoviruses have emerged in nonendemic areas, as exemplified by four Marburg disease outbreaks recorded in Guinea, Ghana, Tanzania, and Equatorial Guinea between 2021 and 2023. Similarly, the Sudan virus has reemerged in Uganda 10 years after the last recorded outbreak. Moreover, several novel bat-derived filoviruses have been discovered in the last 15 years (Lloviu virus, Bombali virus, Měnglà virus, and Dehong virus), most of which are poorly characterized but may display a wide host range. These novel viruses have the potential to cause outbreaks in humans. Several gaps are yet to be addressed regarding known and emerging filoviruses. These gaps include the virus ecology and pathogenicity, mechanisms of zoonotic transmission, host range and susceptibility, and the development of specific medical countermeasures. In this review, we summarize the current knowledge on non-Ebola filoviruses (Bombali virus, Bundibugyo virus, Reston virus, Sudan virus, Tai Forest virus, Marburg virus, Ravn virus, Lloviu virus, Měnglà virus, and Dehong virus) and suggest some strategies to accelerate specific countermeasure development.

Domestic pigs are susceptible to experimental infection with non-human primate-derived Reston virus without the need for adaptation

Domestic pigs are a critical component of the food supply and one of the most commonly raised production animals. Pork consumption has driven the intensification of pig production expanding into environments conducive to increased emergence and spread of infectious diseases, including the spillover of pathogens into human populations. One of these emerging viruses, Reston virus (RESTV), is an enigma among the Orthoebolavirus genus in that its lack of human pathogenicity is in stark contrast to the high virulence associated with most other ebolaviruses. RESTV is, however, associated with outbreaks of highly lethal hemorrhagic disease in non-human primates (NHP), as well as poorly understood clinical manifestations of mixed virulence and lethality in naturally and experimentally infected domestic pigs. Our results show it is possible for RESTV derived from an NHP to infect domestic pigs resulting in a spectrum of disease, from asymptomatic to severe respiratory distress. Further, we report on the first experimental transmission of RESTV between infected pigs and a co-housed, naïve animal, as well as the first report of the successful use of group oral fluids for the detection of RESTV RNA and virus-specific IgA antibodies.

Laboratory Animal Models for Rift Valley Fever Virus Disease

Rift Valley fever virus (RVFV) is an arboviral pathogen of clinical and agricultural relevance. The ongoing development of targeted RVFV prophylactics and therapeutics is overwhelmingly dependent on animal models due to both natural, that is, sporadic outbreaks, and structural, for example, underresourcing of endemic regions, limitations in accessing human patient samples and cohorts. Elucidating mechanisms of viral pathogenesis and testing therapeutics is further complicated by the diverse manifestations of RVFV disease and the heterogeneity of the host response to infection. In this chapter, we describe major clinical manifestations of RVFV infection and discuss the laboratory animal models used to study each.

The Inability of Marburg Virus to Cause Disease in Ferrets Is Not Solely Linked to the Virus Glycoprotein

Ebola virus (EBOV) causes lethal disease in ferrets, whereas Marburg virus (MARV) does not. To investigate this difference, we first evaluated viral entry by infecting ferret spleen cells with vesicular stomatitis viruses pseudotyped with either MARV or EBOV glycoprotein (GP). Both viruses were capable of infecting ferret spleen cells, suggesting that lack of disease is not due to a block in MARV entry. Next, we evaluated replication kinetics of authentic MARV and EBOV in ferret cell lines and demonstrated that, unlike EBOV, MARV was only capable of low levels of replication. Finally, we inoculated ferrets with a recombinant EBOV expressing MARV GP in place of EBOV GP. Infection resulted in uniformly lethal disease within 7-9 days postinfection, while MARV-inoculated animals survived until study endpoint. Together these data suggest that the inability of MARV to cause disease in ferrets is not entirely linked to GP.

Pathogenicity of Lloviu and Bombali Viruses in Type I Interferon Receptor Knockout Mice

Type I interferon receptor knockout (IFNAR-/-) mice are not able to generate a complete innate immune response; therefore, these mice are often considered to assess the pathogenicity of emerging viruses. We infected IFNAR-/- mice with a low or high dose of Lloviu virus (LLOV) or Bombali virus (BOMV) by the intranasal (IN) or intraperitoneal (IP) route and compared virus loads at early and late time points after infection. No signs of disease and no viral RNA were detected after IN infection regardless of LLOV dose. In contrast, IP infections resulted in increased viral loads in the high-dose LLOV and BOMV groups at the early time point. The low-dose LLOV and BOMV groups achieved higher viral loads at the late time point. However, there was 100% survival in all groups and no signs of disease. In conclusion, our results indicate a limited value of the IFNAR-/- mouse model for investigation of the pathogenicity of LLOV and BOMV.

A review of broadly protective monoclonal antibodies to treat Ebola virus disease

The filovirus vaccine and the therapeutic monoclonal antibody (mAb) research have made substantial progress. However, existing vaccines and mAbs approved for use in humans are specific to Zaire ebolavirus (EBOV). Since other Ebolavirus species are a continuing threat to public health, the search for broadly protective mAbs has drawn attention. Here, we review viral glycoprotein-targeting mAbs that have proved their broader protective efficacy in animal models. MBP134^AF, the most advanced of these new-generation mAb therapies, has recently been deployed in Uganda during the Sudan ebolavirus outbreak. Furthermore, we discuss the measures associated with enhancing antibody therapies and the risks associated with them, including the rise of escape mutations following the mAb treatment and naturally occurring EBOV variants.

Immunohistochemical detection of MUC5AC and MUC5B mucins in ferrets

OBJECTIVE

Cystic fibrosis (CF) is a genetic condition that causes abnormal mucus secretions in affected organs. MUC5AC and MUC5B are gel-forming mucins and frequent targets for investigations in CF tissues. Our objective was to qualify MUC5AC and MUC5B immunohistochemical techniques to provide a useful tool to identify, localize and interpret mucin expression in ferret tissues.

RESULTS

MUC5AC and MUC5B mucins were detected most commonly in large airways and least in small airways, consistent with reported goblet cell density in airway surface epithelia. We evaluated whether staining method affected the detection of goblet cell mucins in serial sections of bronchial surface epithelia. Significant differences between stains were not observed suggesting common co-expression MUC5AC and MUC5B proteins in goblet cells of airway surface epithelia. Gallbladder and stomach tissues are reported to have differential mucin enrichment, so we tested these tissues in wildtype ferrets. Stomach tissues were enriched in MUC5AC and gallbladder tissues enriched in MUC5B, mucin enrichment similar to human tissues. Mucin immunostaining techniques were further qualified for specificity using lung tissue from recently generated MUC5AC-/- and MUC5B-/- ferrets. Qualified techniques for MUC5AC and MUC5B immunohistochemistry will be useful tools for mucin tissue studies in CF and other ferret models.

Linked Mutations in the Ebola Virus Polymerase Are Associated with Organ Specific Phenotypes

Ebola virus (EBOV) causes a severe infection called Ebola virus disease (EVD). The pathogenesis of EBOV infection is complex, and outcome has been associated with a variety of immunological and cellular factors. Disease can result from several mechanisms, including direct organ and endothelial cell damage as a result of viral replication. During the2013 to 2016 Western Africa EBOV outbreak, several mutants emerged, with changes in the genes of nucleoprotein (NP), glycoprotein (GP), and the large (L) protein. Reverse genetic analysis has been used to investigate whether these mutations played any role in pathogenesis with mixed results depending on the experimental system used. Previous studies investigated the impact of three single nonsynonymous mutations (GP-A82V, NP-R111C, and L-D759G) on the fatality rate of mouse and ferret models and suggested that the L-D759G mutation decreased the virulence of EBOV. In this study, the effect of these three mutations was further evaluated by deep sequencing to determine viral population genetics and the host response in longitudinal samples of blood, liver, kidney, spleen, and lung tissues taken from the previous ferret model. The data indicated that the mutations were maintained in the different tissues, but the frequency of minor genomic mutations were different. In addition, compared to wild-type virus, the recombinant mutants had different within host effects, where the D759G (and accompanying Q986H) substitution in the L protein resulted in an upregulation of the immune response in the kidney, liver, spleen, and lungs. Together these studies provide insights into the biology of EBOV mutants both between and within hosts. IMPORTANCE Ebola virus infection can have dramatic effects on the human body which manifest in Ebola virus disease. The outcome of infection is either survival or death and in the former group with the potential of longer-term health consequences and persistent infection. Disease severity is undoubtedly associated with the host response, often with overt inflammatory responses correlated with poorer outcomes. The scale of the2013 to 2016 Western African Ebola virus outbreak revealed new aspects of viral biology. This included the emergence of mutants with potentially altered virulence. Biobanked tissue from ferret models of EBOV infected with different mutants that emerged in the Western Africa outbreak was used to investigate the effect of EBOV genomic variation in different tissues. Overall, the work provided insights into the population genetics of EBOV and showed that different organs in an animal model can respond differently to variants of EBOV.

Ferrets: A powerful model of SARS-CoV-2

The rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in recent years not only caused a global pandemic but resulted in enormous social, economic, and health burdens worldwide. Despite considerable efforts to combat coronavirus disease 2019 (COVID-19), various SARS-CoV-2 variants have emerged, and their underlying mechanisms of pathogenicity remain largely unknown. Furthermore, effective therapeutic drugs are still under development. Thus, an ideal animal model is crucial for studying the pathogenesis of COVID-19 and for the preclinical evaluation of vaccines and antivirals against SARS-CoV-2 and variant infections. Currently, several animal models, including mice, hamsters, ferrets, and non-human primates (NHPs), have been established to study COVID-19. Among them, ferrets are naturally susceptible to SARS-CoV-2 infection and are considered suitable for COVID-19 study. Here, we summarize recent developments and application of SARS-CoV-2 ferret models in studies on pathogenesis, therapeutic agents, and vaccines, and provide a perspective on the role of these models in preventing COVID-19 spread.

History and impact of the mouse-adapted Ebola virus model

Ebola virus (EBOV) is a member of the filoviridae family, which are comprised of negative sense, enveloped RNA hemorrhagic fever viruses that can cause severe disease and high lethality rates. These viruses require BSL-4 containment laboratories for study. Early studies of EBOV pathogenesis relied heavily on the use of nonhuman primates, which are expensive and cumbersome to handle in large numbers. Guinea pig models were also developed, but even to this day limited reagents are available in this model. In 1998, Mike Bray and colleagues developed a mouse-adapted EBOV (maEBOV) that caused lethality in adult immunocompetent mice. This model had significant advantages, including being inexpensive, allowing for higher animal numbers for statistical analysis, availability of reagents for studying pathogenesis, and availability of a vast array of genetically modified strains. The model has been used to test vaccines, therapeutic drugs, EBOV mutants, and pathogenesis, and its importance is demonstrated by the hundreds of citations referencing the original publication. This review will cover the history of the maEBOV model and its use in filovirus research.

Of mice and Mike-An underappreciated Ebola virus disease model may have paved the road for future filovirology

In 1998, Mike Bray and colleagues published the first immunocompetent laboratory mouse model of Ebola virus disease. Often labeled by peer reviewers as inferior to large nonhuman primate efforts, this model initially laid the foundation for the recent establishment of panel-derived cross-bred and humanized mouse models and a golden hamster model. Nonhuman primate research has always been associated with ethical concerns and is sometimes deemed scientifically questionable due to the necessarily low animal numbers in individual studies. Independent of these concerns, the now-global severe shortage of commercially available large nonhuman primates may pragmatically push research toward increased and improved rodent modeling that may altogether replace nonhuman primate studies in the short term as well as in an optimal future.

Bridging Animal and Human Data in Pursuit of Vaccine Licensure

The FDA Animal Rule was devised to facilitate approval of candidate vaccines and therapeutics using animal survival data when human efficacy studies are not practical or ethical. This regulatory pathway is critical for candidates against pathogens with high case fatality rates that prohibit human challenge trials, as well as candidates with low and sporadic incidences of outbreaks that make human field trials difficult. Important components of a vaccine development plan for Animal Rule licensure are the identification of an immune correlate of protection and immunobridging to humans. The relationship of vaccine-induced immune responses to survival after vaccination and challenge must be established in validated animal models and then used to infer predictive vaccine efficacy in humans via immunobridging. The Sabin Vaccine Institute is pursuing licensure for candidate filovirus vaccines via the Animal Rule and has convened meetings of key opinion leaders and subject matter experts to define fundamental components for vaccine licensure in the absence of human efficacy data. Here, filoviruses are used as examples to review immune correlates of protection and immunobridging. The points presented herein reflect the presentations and discussions during the second meeting held in October 2021 and are intended to address important considerations for developing immunobridging strategies.

Hemorrhagic Fever Viruses: Pathogenesis and Countermeasures

Before December 2019 and the COVID-19 pandemic, the general public was to some extent aware that zoonotic viruses can spill over into the human population and cause a disease outbreak [...]

Livestock and Risk Group 4 Pathogens: Researching Zoonotic Threats to Public Health and Agriculture in Maximum Containment

Maximum-containment laboratories are a unique and essential component of the bioeconomy of the United States. These facilities play a critical role in the national infrastructure, supporting research on a select set of especially dangerous pathogens, as well as novel, emerging diseases. Understanding the ecology, biology, and pathology at the human-animal interface of zoonotic spillover events is fundamental to efficient control and elimination of disease. The use of animals as human surrogate models or as target-host models in research is an integral part of unraveling the interrelated components involved in these dynamic systems. These models can prove vitally important in determining both viral- and host-factors associated with virus transmission, providing invaluable information that can be developed into better risk mitigation strategies. In this article, we focus on the use of livestock in maximum-containment, biosafety level-4 agriculture (BSL-4Ag) research involving zoonotic, risk group 4 pathogens and we provide an overview of historical associated research and contributions. Livestock are most commonly used as target-host models in high-consequence, maximum-containment research and are routinely used to establish data to assist in risk assessments. This article highlights the importance of animal use, insights gained, and how this type of research is essential for protecting animal health, food security, and the agriculture economy, as well as human public health in the face of emerging zoonotic pathogens. The utilization of animal models in high-consequence pathogen research and continued expansion to include available species of agricultural importance is essential to deciphering the ecology of emerging and re-emerging infectious diseases, as well as for emergency response and mitigation preparedness.

Balancing Animal Welfare, Human Safety, and Research in Agriculture High Containment

Livestock research is paramount to understanding the risks associated with unintentional and intentional introductions of emerging, reemerging, and transboundary animal diseases, including their relationship to both the security of the economy and the nation’s food supply. Research involving large animal species conducted in maximum containment Biosafety Level (BSL)-3Ag and BSL-4 facilities include Health and Human Services and United States Department of Agriculture Select Agents that can have severe consequences on both animal agricultural industry and public health. This themed issue of ILAR spans the spectrum of concerns related to this special niche within the animal research community with an emphasis on a review of available research, current trends, and novel approaches relevant to those conducting large animal research with high-risk agents and those charged with regulating those facilities and programs. Articles are authored by those embedded in the high- and maximum-containment community, directly involved with the work, detailing the unique challenges associated with BSL-3 and BSL-4 livestock research.