Assessing the impact of host and virus genetic variability on Filovirus cell entry and infectivity

The first step in virus infection is entry into a susceptible cell. This almost always involves interaction between proteins at the surface of the virus and the cell and, for viruses surrounded by a lipid envelope, subsequent fusion of the virus and host cell membranes. This step of the virus life cycle is the first barrier encountered when a virus jumps from its natural host into another species. We have recently shown that Ebolavirus rapidly evolves to become better adapted for human cell entry but the mechanism underlying this remains to be elucidated. Although the location of key mutations in and around the host protein (receptor) -binding region of the virus surface protein suggest that receptor binding is a key determinant there is increasing evidence to suggest that other steps, for example fusion, may be affected by virus evolution. In this project we will develop a genetically modified mouse, and utilise a range of in vitro assays to study the infectivity of Ebola and Marburg viruses and define how genetic variation observed in both virus and different hosts affects this process. These findings will help us understand better virus spillover events and enable us to identify genetic signatures that may lead to increased zoonotic risk and subsequent human transmissibility as well as identify human populations that are inherently more at risk from heightened outbreaks. Together these findings will lead to improved future outbreak monitoring and response and also inform development of improved vaccines and therapies.

The West African Ebolavirus outbreak was on an unprecedented scale. There is overwhelming evidence that the risk of future Filovirus outbreaks will increase due to population growth, urbanisation, habitat encroachment and improved transport links. Understanding host and viral factors that influence Ebola and Marburg virus infectivity and outbreak severity will inform future outbreak preparedness, it will also provide important insight into the Filovirus entry process that can guide future therapeutic design; especially interventions that have pan-Filovirus activity. Knowledge of host genetic factors that impact on Filovirus entry efficacy will pave the way for future large-scale genomics studies of Filovirus-exposed populations to determine the impact of host genetic factors, particularly receptor polymorphisms, on human population susceptibility (or resistance) to infection and disease severity. In the long-term this can inform public health policy and also inform patient care. Using the most relevant experimental systems, which will include transgenic mouse models, recombinant infectious VSV-chimeras encoding Filovirus surface glycoproteins, pseudovirus entry, reverse genetics, biochemical assays, cell transduction and live cell imaging, we will determine the impact of virus evolution on host tropism and infectivity. We will also define the impact of inter-species host receptor variation and human allelic variants on Filovirus entry and link these observations to African patient cohorts to determine the possible impact in the context of virus outbreaks. In addition to new understanding of Filovirus infectivity, the project will generate a small animal model to support wider studies of Filovirus entry, a large number of viral clones, genetically modified cell lines and synthetic glycoproteins that will be of wider benefit to the research community, particularly those engaged in treatment and vaccine development.

Emerging infections are a serious global health threat. The Filoviruses Marburg and Ebolavirus are likely to have caused sporadic outbreaks for centuries. They were thought to be fairly small, self-contained and easy to deal with; the recent West African outbreak came as a stark wake-up call. In order to deal with the threat of future outbreaks we need to have a better understanding of the host and viral factors that influence virus spillover and impact on disease severity. This project will address this major shortfall in knowledge and as such provide a number of leads for the development of new therapeutic approaches and insights that will help model future emerging infection outbreaks. It will also generate new tools and technologies - the proposed transgenic small animal model will be particularly useful for researchers interested in defining species-determinants associated with infectivity and transmission and provide vaccine and treatment researchers with much improved model system to test efficacy. The findings generated will impact on a range of stakeholders including basic and applied researchers, public health specialists, clinicians and policy makers.