Table 1. Etiology and epidemiology of CNS infections.
| Pathogen | Geographic distribution | Transmission route | Demographics | Clinical presentation |
|---|---|---|---|---|
| Bacteria | ||||
| Streptococcus agalactiae | Worldwide | Vertical transmission (mother to child) through the birth canal | Neonates | Meningitis |
| Escherichia coli | ||||
| Neisseria meningitidis | Inhalation (droplets produced by coughing or sneezing) | Children and adults | ||
| Streptococcus pneumoniae | ||||
| Haemophilus influenzae | Elderly and immunocompromised individuals | |||
| Listeria monocytogenes | Transplacental | Elderly, immunocompromised, (neonates) | Meningitis, rhombencephalitis | |
| Mycobacterium tuberculosis | Worldwide; vast majority in Africa/Asia | Inhalation (Flugge droplets) | Children and adults Immunocompromised (HIV infected patients) |
Meningitis, cerebral tuberculomas |
| Treponema pallidum (neurosyphilis) | Worldwide | Direct contact (sexual) | Adults | Meningoencephalitis; General paresis; Tabes dorsalis |
| Leptospira spp. | Worldwide | Contact with infected mammals (rodents) | Children and adults | Meningitis; Meningoencephalitis; Myelitis |
| Borrelia burgdorferi (neuroborreliosis) | North America and Eurasia | Arthropod borne (tick: Ixodes spp.) | Children and adults | Encephalitis; Meningitis; Encephalopathy |
| Viruses | ||||
| EV | Worldwide | Fecal/oral Inhalation (EV-D68) |
Children and adults | Meningitis Encephalitis (rare) |
| HSV | Worldwide | Skin/mucosa | Children (mainly HSV1) and adults (mainly HSV2) Immunocompromised |
Meningitis Encephalitis |
| VZV | Worldwide | Skin/mucosa Inhalation |
Adults (mostly immunocompromised) | Encephalitis; Meningitis (rare); Myelitis |
| Mumps virus | Worldwide | Inhalation | Children and adults (mostly unvaccinated) | Meningitis; Myelitis; |
| Rabies virus | Worldwide; vast majority in Africa/Asia | Contact with infected mammal (dogs) | Children and adults | Encephalitis |
| WNV | Worldwide | Arthropod borne (mosquito: Culex spp.) | Children and adults (mostly elderly population) | Meningitis; Encephalitis |
| JEV | Asia, Australia, and western Pacific | Arthropod borne (mosquito: Culex spp.) | Children and adults (mostly pediatric population) | Encephalitis |
| TBEV | Central and northern Europe | Arthropod borne (tick: Ixodes ricinus) | Children and adults | Encephalitis |
| JCV | Worldwide | Inhalation | Adults with severe immune deficiency | PML |
| Fungi | ||||
| Candida spp. (neurocandidiasis) | Worldwide (human commensal) | Nosocomial (neurosurgery, CNS devices) | Preterm neonates, children, and adults | Meningoencephalitis; brain abscesses |
| Cryptococcus neoformans (neurocryptococcosis) | Worldwide; frequent in Europe | Inhalation (bird droppings) | Immunocompromised (especially for CD4+ T-cell counts <100/mm3) | Meningoencephalitis |
| Aspergillus spp. | Worldwide | Inhalation | Immunocompromised | Brain abscesses (frequently secondary to lung infections) |
|
Scedosporium spp. Lomentospora spp. |
Worldwide | Inhalation | Children and adults (mostly immunocompromised) | Brain abscesses (secondary to lung infections or near-drowning) |
| Mucoromycetes (Rhizopus, Lichtheimia, Mucor …) | Worldwide | Inhalation | Immunocompromised | Brain abscesses (frequently secondary to sinus infections) |
| Histoplasma capsulatum (histoplasmosis) | Central and eastern United States (var. capsulatum); Africa (var. duboisii) | Inhalation (bird or bat droppings) | Children and adults (immunocompetent) | Meningitis, meningoencephalitis, and brain abscesses |
| Blastomyces spp. (blastomycosis) | North America | Inhalation (soil dust) | Children and adults (immunocompetent) | Meningitis, meningoencephalitis, and brain abscesses |
| Coccidioides spp. (coccidioidomycosis) | Southwest US, Mexico, and South America | Inhalation (soil dust) | Children and adults (immunocompetent) | Meningitis, meningoencephalitis, and brain abscesses |
| Paracoccidioides spp. (paracoccidioidomycosis) | Central and South America | Inhalation (soil dust) | Children and adults (immunocompetent) | Brain abscesses and meningitis |
| Dematiaceous molds (phaeohyphomycosis) | Worldwide | Inhalation | Children and adults (immunocompetent) | Brain abscesses |
| Parasites | ||||
| Toxoplasma gondii | Worldwide | Ingestion of tissue cysts or sporulated oocysts Organ transplant Blood transfusion |
Immunocompromised (especially for CD4+ T-cell counts <200/mm3) | Encephalitis and brain abscesses |
| Trypanosoma brucei (sleeping disease) | Africa | Arthropod borne (Tsetse flies, Glossinidae) | Children and adults | Mental and behavioral disorders, sleep and sleep–wake cycles disturbances |
| Plasmodium spp. (cerebral malaria) | Tropical and subtropical regions | Arthropod borne (Mosquito: Anopheles spp.) | Children and adults | Impaired consciousness and coma |
| Taenia solium (neurocysticercosis) | Africa, Asia, and Latin America | Fecal–oral | Children and adults (mostly from resource-limited countries) | Intracerebral cysts (epilepsy) |
| Angiostrongylus spp. (neuroangiostrongyliasis) | Southeast Asia, Oceania, and the Americas | Ingestion of terrestrial mollusks (snails/slugs) | Children and adults | Eosinophilic meningitis; Intracranial hemorrhage |
| Gnathostoma spp. (gnathostomiasis) | Southeast Asia, Japan Korea, and Latin America | Food borne (mostly raw freshwater fish, amphibians, and reptiles) | Children and adults | Eosinophilic meningitis; Intracranial hemorrhage |
| Free-living amoebae (Acanthamoeba, Balamuthia and Naegleria) | Worldwide | Inhalation (contaminated water) | Immunocompromised (Acanthamoeba, Balamuthia) Immunocompetent (Naegleria) |
Granulomatous amebic encephalitis (Acanthamoeba, Balamuthia) Primary amebic meningoencephalitis (Naegleria) |
CNS, central nervous system; EV, enterovirus; HSV, herpes simplex virus; JCV, JC virus; JEV, Japanese encephalitis virus; PML, progressive multifocal leukoencephalopathy; TBEV, tick-borne encephalitis virus; VZV, varicella-zoster virus; WNV, West Nile virus.