Figure 3.

Models of ZIKV and SARS-CoV-2 infection of the CNS. When ZIKV is transmitted to a pregnant woman by bites of infected Aedes mosquitoes, although it causes mild or no symptoms in the mother, it enters the bloodstream, breaches the placental barrier, and infects the developing CNS of the fetus, with devastating consequences including microcephaly, decreased brain tissue, damage to the posterior segment of the eye, hypertonia, and arthrogryposis. In vitro experiments with human neurospheres confirm the direct effect of ZIKV on neural cells. Once SARS-CoV-2 is inhaled into the nasal cavity, it infects the sustentacular cells of the olfactory epithelium using ACE2 receptor and multiplies causing infection of the olfactory epithelium, the respiratory epithelium, and olfactory bulb through the numerous ACE2 receptors expressed by the cells of these tissues. From the olfactory bulb, the virus may travel to the CNS by retrograde axonal transport along olfactory sensory neurons.