A neurotropic virus is said to be neuroinvasive if it is capable of accessing or entering the nervous system and neurovirulent if it is capable of causing disease within the nervous system. Both terms are often applied to central nervous system infections, although some neurotropic viruses are highly neuroinvasive for the peripheral nervous system (e.g. herpes simplex virus). Important neuroinvasive viruses include poliovirus, which is highly neurovirulent but weakly neuroinvasive, and rabies virus, which is highly neurovirulent but requires tissue trauma (often resulting from an animal bite) to become neuroinvasive. Using these definitions, herpes simplex virus is highly neuroinvasive for the peripheral nervous system and rarely neuroinvasive for the central nervous system, but in the latter case may cause herpesviral encephalitis and is therefore considered highly neurovirulent. Many arthropod-borne neurotropic viruses, like West Nile virus, spread to the brain primarily via the blood system by crossing the blood–brain barrier in what is called hematogenous dissemination.[citation needed]
Neurotropic viruses are increasingly being exploited as research tools, and for their potential use in treatment. In particular, they are being used to improve the understanding of the nervous systems circuits.[4][5]
