A number of infectious agents can cause neurologic disease including viruses, bacteria, fungi parasites, chlamydia, mycoplasma, rickettsia, and prions. The most common infectious agents to involve the nervous system are viruses.
Viruses can cause acute neurologic syndromes such as meningitis, encephalitis, and poliomyelitis.
They can also cause persistent syndromes of neurologic latent infection slow virus infection. They can infect intraaxonally through a neuronal route such as rabies. They can infect through cranial nerve I, the olfactory nerve such as Herpes simplex. The most common route of entry of a virus to the central nervous system is hematogenous bloodborne spread. Neurotropic viruses have both neurovirulence and neuroinvasiveness factors that help determine whether they cause disease.