The emergence of SARS-CoV-2 has created an international health crisis, and small animal models mirroring SARS-CoV-2 human disease are essential for medical countermeasure (MCM) development. Mice are refractory to SARS-CoV-2 infection owing to low-affinity binding to the murine angiotensin-converting enzyme 2 (ACE2) protein. Here, we evaluated the pathogenesis of SARS-CoV-2 in male and female mice expressing the human ACE2 gene under the control of the keratin 18 promoter (K18). In contrast to nontransgenic mice, intranasal exposure of K18-hACE2 animals to 2 different doses of SARS-CoV-2 resulted in acute disease, including weight loss, lung injury, brain infection, and lethality. Vasculitis was the most prominent finding in the lungs of infected mice. Transcriptomic analysis from lungs of infected animals showed increases in transcripts involved in lung injury and inflammatory cytokines. In the low-dose challenge groups, there was a survival advantage in the female mice, with 60% surviving infection, whereas all male mice succumbed to disease. Male mice that succumbed to disease had higher levels of inflammatory transcripts compared with female mice. To our knowledge, this is the first highly lethal murine infection model for SARS-CoV-2 and should be valuable for the study of SARS-CoV-2 pathogenesis and for the assessment of MCMs.

Animal models are needed to better understand the pathogenic mechanisms of Zika virus (ZIKV) and to evaluate candidate medical countermeasures. Adult mice infected with ZIKV develop a transient viremia, but do not demonstrate signs of morbidity or mortality. Mice deficient in type I or a combination of type I and type II interferon (IFN) responses are highly susceptible to ZIKV infection; however, the absence of a competent immune system limits their usefulness for studying medical countermeasures. Here we employ a murine model for ZIKV using wild-type C57BL/6 mice treated with an antibody to disrupt type I IFN signaling to study ZIKV pathogenesis. We observed 40% mortality in antibody treated mice exposed to ZIKV subcutaneously whereas mice exposed by intraperitoneal inoculation were highly susceptible incurring 100% mortality. Mice infected by both exposure routes experienced weight loss, high viremia, and severe neuropathologic changes. The most significant histopathological findings occurred in the central nervous system where lesions represent an acute to subacute encephalitis/encephalomyelitis that is characterized by neuronal death, astrogliosis, microgliosis, scattered necrotic cellular debris, and inflammatory cell infiltrates. This model of ZIKV pathogenesis will be valuable for evaluating medical countermeasures and the pathogenic mechanisms of ZIKV because it allows immune responses to be elicited in immunologically competent mice with IFN I blockade only induced at the time of infection. Research addressing the severe clinical complications associated with ZIKV infection, including GBS and congenital ZIKV syndrome, are urgently needed. Key to this effort is development of well-characterized animal models that recapitulate human disease. Adult wild-type mice infected with ZIKV can develop viremia in some instances, but they do not emulate the disease associated with the severe congenital and adult neuropathology. Several groups have recently described type I or type II IFN-deficient murine models that are permissive for viral replication in several organs including the brain. The major limitation of these models is they utilize immunodeficient knockout mice lacking key components of the innate antiviral response. We describe the use of a lethal murine model for ZIKV where the innate response of immunocompetent mice is suppressed only at the time of infection. We show that the mice develop severe neurological disease similar to that previously demonstrated in mice deficient in the type I or II IFN response. Using this model, we provide a detailed description of the ZIKV-associated pathologic changes, which mirrors the neuropathogenic properties of ZIKV in humans. These studies provide a baseline for assessment of medical countermeasures that can prevent or treat such pathogenic effects caused by ZIKV infection.

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne virus capable of causing a severe hemorrhagic fever disease in humans. There are currently no licensed vaccines to prevent CCHFV-associated disease. We developed a DNA vaccine expressing the M-segment glycoprotein precursor gene of CCHFV and assessed its immunogenicity and protective efficacy in two lethal mouse models of disease: type I interferon receptor knockout (IFNAR^-/-) mice; and a novel transiently immune suppressed (IS) mouse model. Vaccination of mice by muscle electroporation of the M-segment DNA vaccine elicited strong antigen-specific humoral immune responses with neutralizing titers after three vaccinations in both IFNAR^-/- and IS mouse models. To compare the protective efficacy of the vaccine in the two models, groups of vaccinated mice (7–10 per group) were intraperitoneally (IP) challenged with a lethal dose of CCHFV strain IbAr 10200. Weight loss was markedly reduced in CCHFV DNA-vaccinated mice as compared to controls. Furthermore, whereas all vector-control vaccinated mice succumbed to disease by day 5, the DNA vaccine protected >60% of the animals from lethal disease. Mice from both models developed comparable levels of antibodies, but the IS mice had a more balanced Th1/Th2 response to vaccination. There were no statistical differences in the protective efficacies of the vaccine in the two models. Our results provide the first comparison of these two mouse models for assessing a vaccine against CCHFV and offer supportive data indicating that a DNA vaccine expressing the glycoprotein genes of CCHFV elicits protective immunity against CCHFV. Crimean-Congo hemorrhagic Fever Virus (CCHFV) is a tick-borne virus capable of causing lethal human disease against which there are currently no approved vaccines. In this study, we compared the immunogenicity and protective efficacy of a candidate DNA vaccine expressing the glycoprotein precursor gene of CCHFV in two mouse models. In addition to the recently established IFNAR^-/- mouse pathogenesis model, we also tested the vaccine in a novel murine system in which the interferon (IFN) α/β signaling response of immunocompetent mice is transiently suppressed. We found that the DNA vaccine elicited high humoral immune responses and provided significant protection against challenge with CCHFV in both mouse models. These findings further our understanding of the requirements for a CCHFV vaccine and provide a new mouse model for the development of CCHFV countermeasures.

An antibody targeting the CCHFV GP38 molecule protects adult mice against lethal infection in a severe disease model.

Burkholderia cepacia is an important opportunistic human pathogen that affects immunocompromised individuals, particularly cystic fibrosis (CF) patients. Colonization of the lungs of a CF patient by B. cepacia can lead not only to a decline in respiratory function but also to an acute systemic infection, such as bacteremia. We have previously demonstrated that a CF clinical isolate of B. cepacia , strain J2315, can invade and survive within cultured respiratory epithelial cells. In order to further characterize the mechanisms of invasion of B. cepacia , we screened a transposon-generated mutant library of strain J2315 for mutants defective in invasion of A549 respiratory epithelial cells. Here we describe isolation and characterization of a nonmotile mutant of B. cepacia with reduced invasiveness due to disruption of fliG , which encodes a component of the motor-switch complex of the flagellar basal body. We also found that a defined null mutation in fliI , a gene encoding a highly conserved ATPase required for protein translocation via the flagellar type III secretion system, also resulted in loss of motility and a significant reduction in invasion. Both mutants lacked detectable intracellular flagellin and failed to export detectable amounts of flagellin into culture supernatants, suggesting that disruption of fliG and fliI impaired flagellar biogenesis. The reduction in invasion did not appear to be due to defective adherence of the flagellar mutants to A549 cells, suggesting that functional flagella and motility are required for full invasiveness of B. cepacia . Our findings indicate that flagellum-mediated motility may facilitate penetration of host epithelial barriers by B. cepacia , contributing to establishment of infection and systemic spread of the organism.