North American strains of eastern equine encephalitis virus (NA-EEEV) are the most neurovirulent of the arthropod-borne alphaviruses and one of the most acutely virulent viruses known, causing mortality in 30-70% of symptomatic human cases and almost uniform mortality in equines. Furthermore, NA-EEEV is considered a potential bioweapon and is an NIH Category B priority pathogen and USDA/CDC Select Agent. The endemic range of NA-EEEV is expanding within the US, numbers of human cases are increasing and the virus has recently been isolated from mosquito species with aggressive human feeding behavior, raising the potential for increased outbreaks of severe encephalitis. Yet, no licensed vaccines or antiviral therapeutics are available and the virus remains critically understudied. Human infections are characterized by a limited prodromal disease and rapid onset of encephalitis signs, often observed as the first indication of infection. Recent work has shown that two phenotypes of the virus are largely responsible for the severity of EEEV infection: 1) avoidance of virus particle access to lymphoid tissues and exacerbation of neuron infection due to heparan sulfate receptor binding by the virus; and 2) restriction of EEEV replication in myeloid cells, particularly macrophages and dendritic cells, by binding of the hematopoietic cell-specific microRNA, miR142-3p, to the virus genome. Together, these activities essentially block lymphoid tissue replication by EEEV, greatly suppress innate immune responses and directly promote neuron infection leading to severe and often fatal encephalitis. In this renewal application, we seek to provide an integrated understanding of relationship of HS binding and miR142-3p restriction, to 1) the role of specific proteoglycan receptors in EEEV infectivity in vitro and tropism and disease in vivo; 2) susceptibility of different human and non-human hosts to EEEV replication and disease; and 3) variability of HS binding and miR142-3p restriction phenotypes during infection of mammalian hosts and the effects of this variation on responses of myeloid cells to interactions with EEEV.
Mosquito-vectored eastern equine encephalitis virus (EEEV) causes arguably the most severe acute disease of any endemic virus in North America. Human disease is fatal in 30-70% of human cases and equine disease is nearly uniformly fatal. There are no specific drugs or vaccines to treat human EEEV. Furthermore, the endemic range of EEEV is expanding within the United States and the potential for more widespread human cases is increasing. We have discovered that the replication of EEEV is dramatically inhibited in immune-inductive sites by the combined effects of heparan sulfate (HS) binding and growth restriction by the myeloid cell-specific host microRNA, miR142-3p, which binds to the virus genome. This leads to limited tropism for these cells in vivo, avoidance of innate immune response induction and great exacerbation of the severity of EEEV encephalitis. We propose to provide an integrated understanding the effect of these phenotypes on EEEV replication and disease, thereby, identifying targets for therapeutic intervention and strategies for EEEV vaccine design. Multiple other RNA viruses bind to HS and it is likely that other viruses are similarly affected by host miRNAs such that these studies should have broad applications.
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