ABSTRACT
Humans and other vertebrates have evolved highly sophisticated barrier systems to prevent the entry of potentially harmful substances into the central nervous system (CNS). These structures include the blood-brain barrier (BBB), formed in part by non-fenestrated vascular endothelial cells within the CNS parenchyma, and the blood-cerebrospinal fl uid barrier (BCSFB), comprised of tightly linked mesenchymal or epithelial cells in structures that border CSF-fi lled spaces (Fig. 1). Despite these complex barriers, many viruses have evolved strategies to infect the CNS, which can give rise to acute and chronic diseases such as meningitis, encephalitis, myelitis, paralysis, etc. Some viruses are able to directly manipulate the BBB or BCSFB to enter the CNS, whereas others hijack host immune cells or travel within peripheral nerves. This chapter will begin with a general description of the structure and function of the BBB/BCSFB and follow with a detailed synopsis of the mechanisms used by viruses to bypass these structures in order to infect the CNS.
