Neurovirulence of the Australian outbreak Japanese Encephalitis virus genotype 4 is lower compared to genotypes 2 and 3 in mice and human cortical brain organoids

Abstract

Human infections with Japanese encephalitis virus (JEV) are a leading cause of viral encephalitis, with ≈70,000 symptomatic cases (≈40% with long-term neurological sequelae) and ≈20,000 deaths reported annually, primarily in Asia and the Western Pacific. An outbreak of JEV genotype 4 was also recently reported in Australia, with an isolate (JEVNSW/22) obtained from a stillborn piglet. Herein we characterize the neuropathology of JEVNSW/22, JEVFU (genotype 2) and JEVNakayama (genotype 3) in adult C57BL/6J wild-type mice, mice deficient in interferon regulatory factor 7 (IRF7-/-), and mice deficient in the type I interferon receptor (IFNAR-/-). In C57BL/6J and IRF7-/- mice with lethal outcomes, viral antigen was detected by immunohistochemistry in inter alia the cortex, thalamus and hippocampus. In these mice, histological lesions included neuronal degeneration, neuronal vacuolation, perivascular cuffing, leukocyte infiltrates, hemorrhage, and microgliosis, with apoptosis and astrocyte activation detected by immunohistochemistry. Microgliosis and hemorrhage persisted in some surviving mice ≈3-4 weeks post infection. JEV was universally lethal in IFNAR-/ mice by day 3 with histological signs of brain hemorrhage, but produced no other detectable brain infection or lesions, with NS1 readily detected in blood vessels, but not neurons, by immunohistochemistry. All JEV isolates showed robust productive cytopathic infection of human cortical brain organoids (hBOs), as well as a human neural progenitor cell line (RENcell VM). We thus describe a new IRF7-/-mouse model for JEV, which shows increased penetrance of lethal neuroinvasiveness and recapitulates many aspects human disease. Although less virulent in IRF7-/- mice, JEVNSW/22 retained the capacity to cause lethal encephalitis and to replicate and destroy human neuronal cells.

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