The lack of a mouse model has hampered an understanding of the pathogenesis and immunity of Marburg hemorrhagic fever (MHF), the disease caused by marburgvirus (MARV), and has created a bottleneck in the development of antiviral therapeutics. Primary isolates of the filoviruses, i.e., ebolavirus (EBOV) and MARV, are not lethal to immunocompetent adult mice. Previously, pathological, virologic, and immunologic evaluation of a mouse-adapted EBOV, developed by sequential passages in suckling mice, identified many similarities between this model and EBOV infections in nonhuman primates. We recently demonstrated that serially passaging virus recovered from the liver homogenates of MARV-infected immunodeficient (SCID) mice was highly successful in reducing the time to death in these mice from 50 to 70 days to 7 to 10 days after challenge with the isolate MARV-Ci67, -Musoke, or -Ravn. In this study, we extended our findings to show that further sequential passages of MARV-Ravn in immunocompetent mice caused the MARV to kill BALB/c mice. Serial sampling studies to characterize the pathology of mouse-adapted MARV-Ravn revealed that this model is similar to the guinea pig and nonhuman primate MHF models. Infection of BALB/c mice with mouse-adapted MARV-Ravn caused uncontrolled viremia and high viral titers in the liver, spleen, lymph node, and other organs; profound lymphopenia; destruction of lymphocytes within the spleen and lymph nodes; and marked liver damage and thrombocytopenia. Sequencing the mouse-adapted MARV-Ravn strain revealed differences in 16 predicted amino acids from the progenitor virus, although the exact changes required for adaptation are unclear at this time. This mouse-adapted MARV strain can now be used to develop and evaluate novel vaccines and therapeutics and may also help to provide a better understanding of the virulence factors associated with MARV.

The sequence of pathogenic events identified in this study provides an understanding of the development of disease processes and also may provide new targets for rational prophylactic and chemotherapeutic interventions.

Cynomolgus macaques were exposed to the Angola strain of Lake Victoria Marburg virus (MARV) by aerosol to examine disease course and lethality. Macaques became febrile 4 to 7 days postexposure; the peak febrile response was delayed 1 to 2 days in animals that received a lower dose; viremia coincided with the onset of fever. All 6 macaques succumbed to the infection, with the 3 macaques in the low-dose group becoming moribund on day 9, a day later than the macaques in the high-dose group. Gross pathologic lesions included maculopapular cutaneous rash; pulmonary congestion and edema; pericardial effusion; enlarged, congested, and/or hemorrhagic lymphoid tissues; enlarged friable fatty liver; and pyloric and duodenal congestion and/or hemorrhage. Fibrinous interstitial pneumonia was the most consistent pulmonary change. Lymphocytolysis and lymphoid depletion, as confirmed by TUNEL (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling), were observed in the mediastinal lymph nodes and spleen. MARV antigen was detected in the lungs, mediastinal lymph nodes, spleen, and liver of all animals examined. In infected macaques, nuclear expression of interleukin-33 was lost in pulmonary arteriolar and mediastinal lymph node high endothelial venule endothelial cells; interleukin-33-positive fibroblastic reticular cells in the mediastinal lymph node were consistently negative for MARV antigen. These macaques exhibited a number of features similar to those of human filovirus infections; as such, this model of aerosolized MARV-Angola might be useful in developing medical countermeasures under the Animal Rule.

The filoviruses, Ebola (EBOV) and Marburg (MARV), cause a lethal hemorrhagic fever. Human isolates of MARV are not lethal to immmunocompetent adult mice and, to date, there are no reports of a mouse-adapted MARV model. Previously, a uniformly lethal EBOV-Zaire mouseadapted virus was developed by performing 9 sequential passages in progressively older mice (suckling to adult). Evaluation of this model identified many similarities between infection in mice and nonhuman primates, including viral tropism for antigen-presenting cells, high viral titers in the spleen and liver, and an equivalent mean time to death. Existence of the EBOV mouse model has increased our understanding of host responses to filovirus infections and likely has accelerated the development of countermeasures, as it is one of the only hemorrhagic fever viruses that has multiple candidate vaccines and therapeutics. Here, we demonstrate that serially passaging liver homogenates from MARV-infected severe combined immunodeficient (scid) mice was highly successful in reducing the time to death in scid mice from 50-70 days to 7-10 days after MARVCi67, -Musoke, or -Ravn challenge. We performed serial sampling studies to characterize the pathology of these scid mouse-adapted MARV strains. These scid mouse-adapted MARV models appear to have many similar properties as the MARV models previously developed in guinea pigs and nonhuman primates. Also, as shown here, the scid-adapted MARV mouse models can be used to evaluate the efficacy of candidate antiviral therapeutic molecules, such as phosphorodiamidate morpholino oligomers or antibodies.

Background: Virus-like particle (VLP)-based vaccines have the advantage of being morphologically and antigenically similar to the live virus from which they are derived. Expression of the glycoprotein and VP40 matrix protein from Lake Victoria marburgvirus (MARV) results in spontaneous production of VLPs in mammalian cells. Guinea pigs vaccinated with Marburg virus VLPs (mVLPs) or inactivated MARV (iMARV) develop homologous humoral and T-cell responses and are completely protected from a lethal homologous MARV challenge. Aims & methods:To determine whether mVLPs based on the Musoke (aka Lake Victoria) isolate of MARV could broadly protect against diverse isolates of MARV, guinea pigs were vaccinated with mVLPs or iMARV-Musoke and challenged with MARV-Musoke, -Ravn orCi67. Results: Prior to challenge, the mVLP-and iMARV-vaccinated guinea pigs had high levels of homologous MARV-Musoke and heterologous MARV-Ravn and -Ci67 antibodies. The Musoke-based mVLPs and iMARV vaccines provided complete protection in guinea pigs against viremia, viral replication and pathological changes in tissues, and lethal disease following challenge with MARV-Musoke, -Ravn or -Ci67. Guinea pigs vaccinated with RIBI adjuvant alone and infected with guinea pig-adapted MARV-Musoke, -Ravn or -Ci67 had histopathologic findings similar to those seen in the nonhuman primate model for MARV infection. Based on the strong protection observed in guinea pigs, we next vaccinated cynomolgus macaques with Musoke-based mVLPs and showed the VLP-vaccinated monkeys were broadly protected against three isolates of MARV (Musoke, Ravn and Ci67). Conclusion: Musoke mVLPs are effective at inducing broad heterologous immunity and protection against multiple MARV isolates.