Rachel LaCasse

Host genetic diversity enables Ebola hemorrhagic fever pathogenesis and resistance

Existing mouse models of lethal Ebola virus infection do not reproduce hallmark symptoms of Ebola hemorrhagic fever, neither delayed blood coagulation and disseminated intravascular coagulation nor death from shock, thus restricting pathogenesis studies to nonhuman primates. Here we show that mice from the Collaborative Cross panel of recombinant inbred mice exhibit distinct disease phenotypes after mouse-adapted Ebola virus infection. Phenotypes range from complete resistance to lethal disease to severe hemorrhagic fever characterized by prolonged coagulation times and 100% mortality. Inflammatory signaling was associated with vascular permeability and endothelial activation, and resistance to lethal infection arose by induction of lymphocyte differentiation and cellular adhesion, probably mediated by the susceptibility allele Tek. These data indicate that genetic background determines susceptibility to Ebola hemorrhagic fever. Intercrossed mice infected with Ebola virus show a spectrum of pathology from prolonged coagulation to total resistance. Variety of Ebola symptoms in mice Apart from monkeys, there are no animal models available that show the same symptoms of Ebola virus infection as those of humans. Rasmussen et al. tested the effects of Ebola virus in mice with defined genetic backgrounds in a series of pains-taking experiments performed under stringent biosafety conditions. Resistance and susceptibility to Ebola virus was associated with distinct genetic profiles in inflammation, blood coagulation, and vascular function. This panel of mice could prove valuable for preliminary screens of candidate therapeutics and vaccines. Science, this issue p. 987

Infection with MERS-CoV causes lethal pneumonia in the common marmoset.

The availability of a robust disease model is essential for the development of countermeasures for Middle East respiratory syndrome coronavirus (MERS-CoV). While a rhesus macaque model of MERS-CoV has been established, the lack of uniform, severe disease in this model complicates the analysis of countermeasure studies. Modeling of the interaction between the MERS-CoV spike glycoprotein and its receptor dipeptidyl peptidase 4 predicted comparable interaction energies in common marmosets and humans. The suitability of the marmoset as a MERS-CoV model was tested by inoculation via combined intratracheal, intranasal, oral and ocular routes. Most of the marmosets developed a progressive severe pneumonia leading to euthanasia of some animals. Extensive lesions were evident in the lungs of all animals necropsied at different time points post inoculation. Some animals were also viremic; high viral loads were detected in the lungs of all infected animals, and total RNAseq demonstrated the induction of immune and inflammatory pathways. This is the first description of a severe, partially lethal, disease model of MERS-CoV, and as such will have a major impact on the ability to assess the efficacy of vaccines and treatment strategies as well as allowing more detailed pathogenesis studies.

A Syrian Golden Hamster Model Recapitulating Ebola Hemorrhagic Fever

Ebola hemorrhagic fever (EHF) is a severe viral infection for which no effective treatment or vaccine is currently available. While the nonhuman primate (NHP) model is used for final evaluation of experimental vaccines and therapeutic efficacy, rodent models have been widely used in ebolavirus research because of their convenience. However, the validity of rodent models has been questioned given their low predictive value for efficacy testing of vaccines and therapeutics, a result of the inconsistent manifestation of coagulopathy seen in EHF. Here, we describe a lethal Syrian hamster model of EHF using mouse-adapted Ebola virus. Infected hamsters displayed most clinical hallmarks of EHF, including severe coagulopathy and uncontrolled host immune responses. Thus, the hamster seems to be superior to the existing rodent models, offering a better tool for understanding the critical processes in pathogenesis and providing a new model for evaluating prophylactic and postexposure interventions prior to testing in NHPs.

Pandemic Swine-Origin H1N1 Influenza A Virus Isolates Show Heterogeneous Virulence in Macaques

ABSTRACT The first influenza pandemic of the new millennium was caused by a newly emerged swine-origin influenza virus (SOIV) (H1N1). This new virus is characterized by a previously unknown constellation of gene segments derived from North American and Eurasian swine lineages and the absence of common markers predictive of human adaptation. Overall, human infections appeared to be mild, but an alarming number of young individuals presented with symptoms atypical for seasonal influenza. The new SOIV also showed a sustained human-to-human transmissibility and higher reproduction ratio than common seasonal viruses, altogether indicating a higher pathogenic potential for this newly emerged virus. To study the virulence of the SOIV, we used a recently established cynomolgus macaque model and compared parameters of clinical disease, virology, host responses, and pathology/histopathology with a current seasonal H1N1 virus. We here show that infection of macaques with two genetically similar but clinically distinct SOIV isolates from the early stage of the pandemic (A/Mexico/4108/2009 and A/Mexico/InDRE4487/2009) resulted in upper and lower respiratory tract infections and clinical disease ranging from mild to severe pneumonia that was clearly advanced over the mild infection caused by A/Kawasaki/UTK-4/2009, a current seasonal strain. Unexpectedly, we observed heterogeneity among the two SOIV isolates in virus replication, host transcriptional and cytokine responses, and disease progression, demonstrating a higher pathogenic potential for A/Mexico/InDRE4487/2009. Differences in virulence may explain more severe disease, as was seen with certain individuals infected with the emerged pandemic influenza virus. Thus, the nonhuman primate model closely mimics influenza in humans.

Host Response Dynamics Following Lethal Infection of Rhesus Macaques With Zaire ebolavirus

To gain further insight into the interdependent pathogenic processes in Ebola hemorrhagic fever (EHF), we have examined the dynamics of host responses in individual rhesus macaques infected with Zaire ebolavirus over the entire disease course. Examination of coagulation parameters revealed that decreased coagulation inhibitor activity triggered severe coagulopathy as indicated by prolonged coagulation times and decreased fibrinogen levels. This has been proposed as one of the significant mechanisms underlying disseminated intravascular coagulation in EHF patients. Furthermore, monitoring of expression levels for cytokines/chemokines suggested a mixed anti-inflammatory response syndrome (MARS), which indicates that a catastrophic uncontrolled immunological status contributes to the development of fatal hemorrhagic fever. These results highlight the pathological analogies between EHF and severe sepsis and not only contribute to our understanding of the pathogenic process, but will also help to establish novel postexposure treatment modalities.

A Hendra Virus G Glycoprotein Subunit Vaccine Protects African Green Monkeys from Nipah Virus Challenge

The Hendra virus attachment G glycoprotein fully protects nonhuman primates from lethal Nipah virus challenge. The Ecology of Disease As people expanded their settlements further and further into the flying fox territory, no one could have suspected that the furry fruit-loving bats carried deadly viruses that can cause human epidemics with mortality rates approaching 100%. The recently discovered (and closely related) Nipah and Hendra viruses can infect humans and a wide range of other species, including domestic animals such as horses, pigs, and dogs; and Nipah is known for person-to-person transmission. Since their discovery in the 1990s, outbreaks have been reported nearly every year, particularly in Bangladesh, India, and Australia, and no effective treatment or prevention method currently exists. Now, Bossart et al. show that a vaccine targeting both viruses shows full protection against Nipah virus in a nonhuman primate model. Nipah virus infection in African green monkeys results in symptoms similar to human disease, with severe involvement of the lungs and brain, and multiple other organ systems, leading to a universally lethal outcome. Here, a recombinant vaccine made from the attachment envelope glycoprotein of Hendra virus is used to prevent infection in the monkeys. The animals are vaccinated with this glycoprotein at a range of doses, but the authors find that even the lowest dose they use provides full protection from Nipah virus challenge. In contrast, the control monkey quickly develops diffuse organ involvement and lethal disease, consistent with historic data. These results demonstrate the feasibility of using immunization to prevent infection with Nipah virus and advance the vaccine one step closer to clinical trials in human subjects. In the 1990s, Hendra virus and Nipah virus (NiV), two closely related and previously unrecognized paramyxoviruses that cause severe disease and death in humans and a variety of animals, were discovered in Australia and Malaysia, respectively. Outbreaks of disease have occurred nearly every year since NiV was first discovered, with case fatality ranging from 10 to 100%. In the African green monkey (AGM), NiV causes a severe lethal respiratory and/or neurological disease that essentially mirrors fatal human disease. Thus, the AGM represents a reliable disease model for vaccine and therapeutic efficacy testing. We show that vaccination of AGMs with a recombinant subunit vaccine based on the henipavirus attachment G glycoprotein affords complete protection against subsequent NiV infection with no evidence of clinical disease, virus replication, or pathology observed in any challenged subjects. Success of the recombinant subunit vaccine in nonhuman primates provides crucial data in supporting its further preclinical development for potential human use.

Resistance to Chronic Wasting Disease in Transgenic Mice Expressing a Naturally Occurring Allelic Variant of Deer Prion Protein

ABSTRACT Prion protein (PrP) is a required factor for susceptibility to transmissible spongiform encephalopathy or prion diseases. In transgenic mice, expression of prion protein (PrP) from another species often confers susceptibility to prion disease from that donor species. For example, expression of deer or elk PrP in transgenic mice has induced susceptibility to chronic wasting disease (CWD), the prion disease of cervids. In the current experiments, transgenic mice expressing two naturally occurring allelic variants of deer PrP with either glycine (G) or serine (S) at residue 96 were found to differ in susceptibility to CWD infection. G96 mice were highly susceptible to infection, and disease appeared starting as early as 160 days postinfection. In contrast, S96 mice showed no evidence of disease or generation of disease-associated protease-resistant PrP (PrPres) over a 600-day period. At the time of clinical disease, G96 mice showed typical vacuolar pathology and deposition of PrPres in many brain regions, and in some individuals, extensive neuronal loss and apoptosis were noted in the hippocampus and cerebellum. Extraneural accumulation of PrPres was also noted in spleen and intestinal tissue of clinically ill G96 mice. These results demonstrate the importance of deer PrP polymorphisms in susceptibility to CWD infection. Furthermore, this deer PrP transgenic model is the first to demonstrate extraneural accumulation of PrPres in spleen and intestinal tissue and thus may prove useful in studies of CWD pathogenesis and transmission by oral or other natural routes of infection.

A synthetic consensus anti–spike protein DNA vaccine induces protective immunity against Middle East respiratory syndrome coronavirus in nonhuman primates

A consensus MERS spike protein synthetic DNA vaccine can induce protective responses against viral challenge. Emerging vaccines Public outcry drives vaccine research during outbreaks of emerging infectious disease, but public support for vaccine development dries up when the outbreaks are resolved, frequently leaving promising vaccine candidates sitting on the shelf. DNA vaccines, with their potential for rapid large-scale production, may help overcome this hurdle. Muthumani et al. report the development of a synthetic DNA vaccine against Middle East respiratory syndrome coronavirus (MERS-CoV) that induces neutralizing antibodies in mice, macaques, and camels—natural hosts of MERS-CoV. Indeed, macaques vaccinated with this DNA vaccine were protected from viral challenge. These promising results support further development of DNA vaccines for emerging infections. First identified in 2012, Middle East respiratory syndrome (MERS) is caused by an emerging human coronavirus, which is distinct from the severe acute respiratory syndrome coronavirus (SARS-CoV), and represents a novel member of the lineage C betacoronoviruses. Since its identification, MERS coronavirus (MERS-CoV) has been linked to more than 1372 infections manifesting with severe morbidity and, often, mortality (about 495 deaths) in the Arabian Peninsula, Europe, and, most recently, the United States. Human-to-human transmission has been documented, with nosocomial transmission appearing to be an important route of infection. The recent increase in cases of MERS in the Middle East coupled with the lack of approved antiviral therapies or vaccines to treat or prevent this infection are causes for concern. We report on the development of a synthetic DNA vaccine against MERS-CoV. An optimized DNA vaccine encoding the MERS spike protein induced potent cellular immunity and antigen-specific neutralizing antibodies in mice, macaques, and camels. Vaccinated rhesus macaques seroconverted rapidly and exhibited high levels of virus-neutralizing activity. Upon MERS viral challenge, all of the monkeys in the control-vaccinated group developed characteristic disease, including pneumonia. Vaccinated macaques were protected and failed to demonstrate any clinical or radiographic signs of pneumonia. These studies demonstrate that a consensus MERS spike protein synthetic DNA vaccine can induce protective responses against viral challenge, indicating that this strategy may have value as a possible vaccine modality against this emerging pathogen.

Pathogenesis and Host Response in Syrian Hamsters following Intranasal Infection with Andes Virus

Hantavirus pulmonary syndrome (HPS), also referred to as hantavirus cardiopulmonary syndrome (HCPS), is a rare but frequently fatal disease caused by New World hantaviruses. In humans HPS is associated with severe pulmonary edema and cardiogenic shock; however, the pathogenesis of this disease remains unclear largely due to a lack of suitable animal models for the study of disease progression. In this study we monitored clinical, virological, pathophysiological parameters and host immunological responses to decipher pathological factors and events in the lethal Syrian hamster model of HPS following intranasal inoculation of Andes virus. Transcriptional profiling of the host gene responses demonstrated a suppression of innate immune responses in most organs analyzed during the early stage of infection, except for in the lung which had low level activation of several pro-inflammatory genes. During this phase Andes virus established a systemic infection in hamsters, with viral antigen readily detectable in the endothelium of the majority of tissues analyzed by 7–8 days post-inoculation. Despite wide-spread infection, histological analysis confirmed pathological abnormalities were almost exclusively found in the lungs. Immediately preceding clinical signs of disease, intense activation of pro-inflammatory and Th1/Th2 responses were observed in the lungs as well as the heart, but not in peripheral organs, suggesting that localized immune-modulations by infection is paramount to pathogenesis. Throughout the course of infection a strong suppression of regulatory T-cell responses was noted and is hypothesized to be the basis of the aberrant immune activations. The unique and comprehensive monitoring of host immune responses to hantavirus infection increases our understanding of the immuno-pathogenesis of HPS and will facilitate the development of treatment strategies targeting deleterious host immunological responses.

Protective Efficacy of a Bivalent Recombinant Vesicular Stomatitis Virus Vaccine in the Syrian Hamster Model of Lethal Ebola Virus Infection

BACKGROUND Outbreaks of filoviral hemorrhagic fever occur sporadically and unpredictably across wide regions in central Africa and overlap with the occurrence of other infectious diseases of public health importance. METHODS As a proof of concept we developed a bivalent recombinant vaccine based on vesicular stomatitis virus (VSV) expressing the Zaire ebolavirus (ZEBOV) and Andes virus (ANDV) glycoproteins (VSVΔG/Dual) and evaluated its protective efficacy in the common lethal Syrian hamster model. Hamsters were vaccinated with VSVΔG/Dual and were lethally challenged with ZEBOV or ANDV. Time to immunity and postexposure treatment were evaluated by immunizing hamsters at different times prior to and post ZEBOV challenge. RESULTS A single immunization with VSVΔG/Dual conferred complete and sterile protection against lethal ZEBOV and ANDV challenge. Complete protection was achieved with an immunization as close as 3 days prior to ZEBOV challenge, and 40% of the animals were even protected when treated with VSVΔG/Dual one day postchallenge. In comparison to the monovalent VSV vaccine, the bivalent vaccine has slightly reduced postexposure efficacy most likely due to its restricted lymphoid organ replication. CONCLUSIONS Bivalent VSV vectors are a feasible approach to vaccination against multiple pathogens.