Table 2.

Routes of Pathogen Entry to the CNS

Mechanism	Bacteria	Fungal	Parasites	Viruses
Retrograde transport along axons	None	None	None	Rabies virus (Bauer et al., 2014) Herpes simplex viruses (Kramer and Enquist, 2013) West Nile virus (Maximova et al., 2016) Venezuelan equine encephalitis virus (Trabalza et al., 2013)
Transendothelial entry within CSF compartment	Group B strep (Kim et al., 2015, Schaeffer et al., 2009) M. tuberculosis (Wu et al., 2000) L. monocytogenes (Dinner et al., 2017) N. meningitides (Schwerk et al., 2012) T. pallidum (Castro et al., 2016)		Angiostrongylus cantonensis (Barratt et al., 2016)	Enteroviruses (Dahm et al., 2016) Measles virus Chikungunya virus Venezuelan/Western equine encephalitis viruses (Phillips et al., 2016)
Paracellular entry at the BBB	L. monocytogenes (Dinner et al., 2017) Nocardia species (Beaman and Ogata, 1993)	Candida albicans (van Sorge and Doran, 2012) Aspergillus niger Zygomycetes Fusarium species Pseudallescheria boydii Pigmented molds Histoplasma capsulatum Coccidioides immitis Penicillium marneffei		Herpes simplex viruses (Dahm et al., 2016) West Nile virus Japanese encephalitis virus Human immunodeficiency virus Poliovirus
Transendothelial entry at the BBB	S. pneumococcus (Iovino et al., 2013)		T. gondii (Konradt et al., 2016) Taenia solium (Marzal et al., 2014)	Influenza A (Dahm et al., 2016)) West Nile virus Venezuelan/Eastern equine encephalitis viruses Rabies virus
CNS entry via infected leukocytes (Trojan Horse)	L. monocytogenes (Drevets et al., 2004)	C. neoformans (Santiago-Tirado et al., 2017)	T. gondii (Konradt et al., 2016)