Investigation of neuropathogenesis and control of an equine-pathogenic Australian West Nile virus isolate in an established CD1 Swiss white mouse and a novel rabbit model

Abstract

West Nile virus (WNV) is a globally significant mosquito-borne neurotropic virus. In 2011, a large-scale arboviral encephalitis outbreak occurred in Australia, involving close to 1000 horses. A virulent WNV strain, WNV NSW2011 , was isolated from the brain of an encephalitic horse during this outbreak. Preliminary assessment showed that this strain is intermediate in virulence and belongs in the same lineage as the highly virulent North American strains. However, the pathogenesis of WNV in general, let alone this novel Australian strain, remains largely unclear.The first part of the project aimed to investigate the pathogenesis of lethal WNV NSW2011 infection in the established young adult Swiss white (CD1) mouse model, since previous survival challenge experiments demonstrated high lethality (~70%) of WNV NSW2011 in this animal model. I conducted a pilot time-course experiment, which demonstrated only benign pathological and virological outcomes in sacrificed mice on day 3 and 7 post-infection (pi), despite the relatively high lethality seen in previous survival trials. In a subsequent experiment, I characterised the disease phenotype in moribund/dead and surviving mice after WNV NSW2011 infection. Notably, I detected a high degree of intra-group variability in the neuropathology, neural infection and glial cell activation. Even cases with neuroinvasion are typically not fatal, unless underlying co-morbidities or immunosuppressive disease exist.I chose rabbits as a candidate for a novel animal model, due to the ease of performing intra-vital sampling and monitoring, as well as the possibility for tissue sharing in different assays, given the larger size of rabbits than mice. Rabbits are also hind-gut fermenters, and thus may be a better representation of a horse than a mouse. New Zealand White (NZWRs; Oryctolagus cuniculus) and iii North American cottontail rabbits (CTRs; Sylvilagus sp.) were challenged with WNV strains of different virulence (WNV NSW2011 and WNV TX8667 ), and the prototype Murray Valley encephalitis virus strain (MVE 1-51 ), by the footpad route. The rabbits were consistently resistant to developing severe disease after virulent WNV and MVEV infection, regardless of age, gender and species, despite productive virus replication in the draining popliteal lymph node (PLN). The resultant viraemia for all rabbits was also of low magnitude and transient. Furthermore, establishment of virus infection in the brain was not a feature of the disease, despite mild to moderate neuropathology in a subset of rabbits. This capacity to control flavivirus infection may be explained by the rapid antiviral innate immune response detectable by day 3 pi, as well as a fast anti-WNV neutralising antibody response detectable from day 7 pi.Comparisons of the tissue-specific transcriptional profile of important cytokine and chemokine genes suggested that virus control in rabbits was achieved differently depending on the virus, as well as the rabbit species. However, common transcriptional upregulation of IFNγ in...

West Nile Virus: An Update on Pathobiology, Epidemiology, Diagnostics, Control and “One Health” Implications

“…The pathological diagnosis has always been useful in the clinical and experimental investigation of WNV infections. This diagnostic approach hinges on detection of macroscopic and microscopic lesions as well as the detection of viral antigen in histological tissue sections using IHC techniques [ 108 , 264 , 320 , 413 , 414 , 415 ]. IHC based on the NS1 or NS3 protein offers the most conclusive, definitive diagnosis as it confirms viral replication in tissues.…”