Molecular mechanisms of eastern equine encephalitis virus pathogenesis

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ABSTRACT 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.