A neurotropic virus is a

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

that is capable of infecting

nerve tissue Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the brain ...

Terminology

A neurotropic virus is said to be neuroinvasive if it is capable of accessing or entering the

nervous system In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...

and neurovirulent if it is capable of causing disease within the nervous system. Both terms are often applied to

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

infections, although some neurotropic viruses are highly neuroinvasive for the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...

(e.g.

herpes simplex virus Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) are two members of the Herpesviridae#Human herpesvirus types, human ''Herpesviridae'' family, a set of viruses that produce Viral disease, viral infections in the majority of humans. Both HSV-1 a ...

). Important neuroinvasive viruses include

poliovirus Poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species '' Enterovirus C'', in the family of '' Picornaviridae''. There are three poliovirus serotypes, numbered 1, 2, and 3. Poliovirus is composed ...

, which is highly neurovirulent but weakly neuroinvasive, and

rabies virus Rabies virus (''Lyssavirus rabies'') is a neurotropic virus that causes rabies in animals, including humans. It can cause violence, hydrophobia, and fever. Rabies transmission can also occur through the saliva of animals and less commonly throu ...

, 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 Herpes simplex encephalitis (HSE), or simply herpes encephalitis, is encephalitis due to herpes simplex virus. It is estimated to affect at least 1 in 500,000 individuals per year, and some studies suggest an incidence rate of 5.9 cases per 100,00 ...

and is therefore considered highly neurovirulent. Many arthropod-borne neurotropic viruses, like

West Nile virus West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...

, spread to the brain primarily via the

blood system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart an ...

by crossing the

blood–brain barrier The blood–brain barrier (BBB) is a highly selective semipermeable membrane, semipermeable border of endothelium, endothelial cells that regulates the transfer of solutes and chemicals between the circulatory system and the central nervous system ...

in what is called hematogenous dissemination.

Examples

Neurotropic viruses that cause infection include

Japanese Encephalitis Japanese encephalitis (JE) is an infection of the brain caused by the Japanese encephalitis virus (JEV). While most infections result in little or no symptoms, occasional inflammation of the brain occurs. In these cases, symptoms may include he ...

Venezuelan Equine Encephalitis Venezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis (VEE). VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may ...

, and California encephalitis viruses;

polio Poliomyelitis ( ), commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 75% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe ...

, coxsackie,

echo In audio signal processing and acoustics, an echo is a reflection of sound that arrives at the listener with a delay after the direct sound. The delay is directly proportional to the distance of the reflecting surface from the source and the lis ...

mumps MUMPS ("Massachusetts General Hospital Utility Multi-Programming System"), or M, is an imperative, high-level programming language with an integrated transaction processing key–value database. It was originally developed at Massachusetts Gen ...

measles Measles (probably from Middle Dutch or Middle High German ''masel(e)'', meaning "blemish, blood blister") is a highly contagious, Vaccine-preventable diseases, vaccine-preventable infectious disease caused by Measles morbillivirus, measles v ...

influenza Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These sympto ...

and

rabies Rabies is a viral disease that causes encephalitis in humans and other mammals. It was historically referred to as hydrophobia ("fear of water") because its victims panic when offered liquids to drink. Early symptoms can include fever and abn ...

, as well as diseases caused by members of the family

Herpesviridae ''Orthoherpesviridae'', previously named and more widely known as ''Herpesviridae'', is a large family of DNA viruses that cause infections and certain diseases in animals, including humans. The members of this family are commonly known as herp ...

such as

herpes simplex Herpes simplex, often known simply as herpes, is a viral disease, viral infection caused by the herpes simplex virus. Herpes infections are categorized by the area of the body that is infected. The two major types of herpes are Cold sore, ora ...

, varicella-zoster, Epstein–Barr,

cytomegalovirus ''Cytomegalovirus'' (CMV) (from ''cyto-'' 'cell' via Greek - 'container' + 'big, megalo-' + -''virus'' via Latin 'poison') is a genus of viruses in the order '' Herpesvirales'', in the family '' Herpesviridae'', in the subfamily '' Betaherp ...

and

HHV-6 Human herpesvirus 6 (HHV-6) is the common collective name for human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B). These closely related viruses are two of the nine known herpesviruses that have humans as their primary host. HHV-6 ...

viruses. All seven of the known human

coronavirus Coronaviruses are a group of related RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the comm ...

es are neurotropic, the

common cold The common cold, or the cold, is a virus, viral infectious disease of the upper respiratory tract that primarily affects the Respiratory epithelium, respiratory mucosa of the human nose, nose, throat, Paranasal sinuses, sinuses, and larynx. ...

viruses mainly in vulnerable populations while the more virulent

SARS-CoV-1 Severe acute respiratory syndrome coronavirus 1 (SARS-CoV-1), previously known as severe acute respiratory syndrome coronavirus (SARS-CoV), is a strain (biology), strain of coronavirus that causes severe acute respiratory syndrome (SARS), the ...

MERS Middle East respiratory syndrome (MERS) is a viral respiratory infection caused by '' Middle East respiratory syndrome–related coronavirus'' (MERS-CoV). Symptoms may range from none, to mild, to severe depending on age and risk level. Typi ...

, and

SARS-CoV-2 Severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2) is a strain of coronavirus that causes COVID-19, the respiratory illness responsible for the COVID-19 pandemic. The virus previously had the Novel coronavirus, provisional nam ...

frequently attack the nervous systems (primarily in animal models). Those causing latent infection include herpes simplex and varicella-zoster viruses. Those causing slow virus infection include

measles virus The measles virus (MV), with scientific name ''Morbillivirus hominis'', is a single-stranded, negative-sense, enveloped, non-segmented RNA virus of the genus ''Morbillivirus'' within the family ''Paramyxoviridae''. It is the cause of measles. H ...

rubella Rubella, also known as German measles or three-day measles, is an infection caused by the rubella virus. This disease is often mild, with half of people not realizing that they are infected. A rash may start around two weeks after exposure and ...

and JC viruses, and

retrovirus A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. After invading a host cell's cytoplasm, the virus uses its own reverse transcriptase e ...

es such as

human T-lymphotropic virus The primate T-lymphotropic viruses (PTLVs) are a group of retroviruses that infect primates, using their lymphocytes to reproduce. The ones that infect humans are known as human T-lymphotropic virus (HTLV), and the ones that infect Old World monk ...

1 and

HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the im ...

Research use

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.

Other neurotropic infections

Several diseases, including

transmissible spongiform encephalopathy Transmissible spongiform encephalopathies (TSEs), also known as prion diseases, are a group of progressive, incurable, and fatal conditions that are associated with the prion hypothesis and affect the brain and nervous system of many animals, in ...

, kuru, and

Creutzfeldt–Jakob disease Creutzfeldt–Jakob disease (CJD) is an incurable, always fatal neurodegenerative disease belonging to the transmissible spongiform encephalopathy (TSE) group. Early symptoms include memory problems, behavioral changes, poor coordination, visu ...

resemble a slow neurotropic virus infection—but are, in fact, caused by the infectious proteins known as

prions A prion () is a misfolded protein that induces misfolding in normal variants of the same protein, leading to cellular death. Prions are responsible for prion diseases, known as transmissible spongiform encephalopathy (TSEs), which are fat ...

References

{{reflist Viruses

Terminology

Examples

Research use

Other neurotropic infections

See also

References