**2. Routes of infection emanating to neurotropic virus infection**

The term "neurotropic" refers to affinity towards the nervous system and displays the properties of neuroinvasion (entry into the CNS), and has direct neuroglial tropism. The viral entry to the neuroglial cells may be via receptor-mediated endocytosis and its fusion with the cell cytoplasm. It may also enter via direct endocytosis irrespective of engaging a receptor. Mounting shreds of evidence reported that neurotropic virus enters the brain parenchyma from the olfactory epithelium or retinal ganglionic cells via retrograded axonal transport. Upon entry to the brain parenchyma, infectious virus particles may also follow anterograde axonal transport via the optic nerve to reach retinal ganglionic cells and also can spread to different anatomic regions of the brain like the hippocampus, cortex, anterior commissure, basal forebrain, amygdala, brain stem as well as down the spinal cord. The neurotropic viruses can also travel through the lung-brain axis and cause inflammation in the brain stem region, the respiratory center. Neurotropic viruses can also access brain parenchyma via the gut-brain axis through the vagus nerve.
