Most central nervous system (CNS) pathogens infect the nervous system nonspecifically, and disease is the result of the brain’s immune response. This is exemplified by viral and bacterial meningitis, which cause extensive inflammation of the brain or its coverings. However, some pathogens show neural tropism and specifically infect certain neurons, as illustrated by motor neuron infections underlying poliomyelitis, neurosyphilis, or infection of sensory neurons by herpes simplex. Similarly, infestation of the brain by larvae (cysticerci) from intestinal tapeworms nonspecifically causes neurological disease in millions of people in the developing world, whereas rare paralytic amoeba actively invade the brain through the nasal canal and feast on brain tissue. By far the most important neurological disease caused by a pathogen is neuro-acquired immunodeficiency syndrome (AIDS), the development of cognitive decline and dementia in the late stages of AIDS due to brain infection with the human immunodeficiency virus. Given the magnitude of the global AIDS endemic, these cases will soon rival more traditional age-related dementia. Neuroscientists are unlikely to contribute to the development of more effective treatments, a task that rests on microbiologists and immunologists who do develop vaccines and antivirals. However, several neurotoxins (Botox) and neurotropic viruses (herpes simplex virus 1) are providing tools to treat neurological disease through targeted delivery of genes or paralytic therapeutics.
Diseases of the Nervous System (Second Edition) 2022, Pages 235-255,