virus /vi·rus/ (vi´rus) [L.] a minute infectious agent which, with certain exceptions, is not resolved by the light microscope, lacks independent metabolism and is able to replicate only within a living host cell; the individual particle (virion) consists of nucleic acid (nucleoid)—DNA or RNA (but not both)—and a protein shell (capsid), which contains and protects the nucleic acid and which may be multilayered.
naked virus
attenuated virus one whose pathogenicity has been reduced by serial passage or other means.
Bayou virus a virus of the genus Hantavirus that causes hantavirus pulmonary syndrome in the southwestern United States.
BK virus (BKV) a human polyomavirus that causes widespread infection in childhood and remains latent in the host; it is believed to cause hemorrhagic cystitis and nephritis in immunocompromised patients.
Central European encephalitis virus a species of tick-borne viruses of the genus Flavivirus that includes the agents of Central European encephalitis and the Russian spring-summer encephalitis virus.
cowpox virus a virus of the genus Orthopoxvirus that is the etiologic agent of cowpox.
Coxsackie virus coxsackievirus.
defective virus one that cannot be completely replicated or cannot form a protein coat; in some cases replication can proceed if missing gene functions are supplied by other viruses; see helper v.
dengue virus a flavivirus existing as four distinct types (designated 1, 2, 3, and 4) that causes dengue.
DNA virus one whose genome consists of DNA.
eastern equine encephalomyelitis virus see equine encephalomyelitis v.
EB virus Epstein-Barr v.
Ebola virus
1. an RNA virus almost identical to the Marburg virus but serologically distinct; it causes a similar disease.
2. a virus of the genus Filovirus that is the etiologic agent of Ebola virus disease.
EEE virus eastern equine encephalomyelitis v.; see equine encephalomyelitis v.
encephalomyocarditis virus an enterovirus that causes mild aseptic meningitis and encephalomyocarditis.
enteric viruses an epidemiologic class of viruses that are normally acquired by ingestion and replicate in the intestinal tract, causing local rather than generalized infection.
enveloped virus a virus having an outer lipoprotein bilayer acquired by budding through the host cell membrane.
Epstein-Barr virus (EBV) human herpesvirus 4; a virus that causes infectious mononucleosis and is associated with Burkitt's lymphoma and nasopharyngeal carcinoma.
equine encephalomyelitis virus a group of arbovirus species of the genus Alphavirus that cause encephalomyelitis in horses, mules, and humans, transmitted by mosquitoes; there are three strains: eastern, western, and Venezuelan.
fixed virus one whose virulence and incubation period have been stabilized by serial passage and remained fixed during further transmission.
foamy viruses Spumavirus.
helper virus one that aids in the development of a defective virus by supplying or restoring the activity of the viral gene or enabling it to form a protein coat.
hepatitis virus the etiologic agent of viral hepatitis. Six types are recognized: hepatitis A virus, the agent causing infectious hepatitis, acquired by parenteral inoculation or by ingestion; hepatitis B virus, the agent causing serum hepatitis, transmitted by inadequately sterilized syringes and needles, or through infectious blood plasma, or certain blood products; hepatitis C virus, which causes hepatitis C; hepatitis D virus, a defective RNA viral agent that can replicate only in the presence of hepatitis B virus and is transmitted with it and causes hepatitis D; hepatitis E virus, a calicivirus transmitting hepatitis E; and hepatitis G virus, flavivirus isolated from patients with hepatitis but whose etiologic role is uncertain.
hepatitis B–like viruses Hepadnaviridae.
herpes virus herpesvirus.
herpes simplex virus (HSV) a virus of the genus Simplexvirus that is the etiologic agent of herpes simplex in humans. It is separable into two serotypes, designated 1 and 2 (called also human herpesvirus 1 and human herpesvirus 2 ); type 1 is transmitted by infected saliva and causes primarily nongenital lesions, and type 2 is sexually transmitted and causes primarily genital lesions.
human immunodeficiency virus (HIV) a human T-cell leukemia/lymphoma virus, of the genus Lentivirus, with a selective affinity for helper T cells that is the agent of the acquired immunodeficiency syndrome.
human T-cell leukemia virus human T-lymphotropic v.
human T-lymphotropic virus 1 (HTLV-1) a species of retroviruses of worldwide distribution, having an affinity for helper/inducer T lymphocytes; it causes chronic infection and is associated with adult T-cell leukemia and chronic progressive myelopathy.
human T-lymphotropic virus 2 (HTLV-2) a species of retroviruses having extensive serologic cross-reactivity with HTLV-1; no clear association with disease has been established.
igbo-ora virus an arbovirus of the genus Alphavirus that has been associated with a dengue-like disease in Nigeria, the Central African Republic, and the Ivory Coast.
influenza virus any of a group of orthomyxoviruses that cause influenza, including at least three genera: Influenzavirus A, Influenzavirus B, and Influenzavirus C. Serotype A viruses are subject to major antigenic changes (antigenic shifts) as well as minor gradual antigenic changes (antigenic drift) and cause the major pandemics.
influenza A virus , influenza B virus, influenza C virus species in the genera Influenzavirus A, Influenzavirus B, and Influenzavirus C; see influenza v.
Jamestown Canyon virus a virus of the genus Bunyavirus, serologically related to California encephalitis virus, that occasionally causes encephalitis.
JC virus (JCV) a polyomavirus that causes widespread infection in childhood and remains latent in the host; it is the cause of progressive multifocal leukoencepahalopathy.
La Crosse virus a virus of the California serogroup of the genus Bunyavirus, the etiologic agent of La Crosse encephalitis.
lymphocyte-associated virus any virus of the subfamily Gammaherpesviridae, members of which are specific for either B or T lymphocytes; infection is often arrested at a lytic or prelytic stage without production of infectious virions, and latent virus may frequently be demonstrated in lymphoid tissue.
lytic virus one that is replicated in the host cell and causes death and lysis of the cell.
Marburg virus an RNA virus occurring in Africa, transmitted by insect bite and causing Marburg disease.
masked virus a virus that ordinarily occurs in a noninfective state and is demonstrable by indirect methods which activate it, as by blind passage in experimental animals.
measles virus a paramyxovirus that is the cause of measles.
measles-like viruses Morbillivirus.
monkeypox virus an orthopoxvirus that produces mild exanthematous disease in monkeys and a smallpox-like disease in humans.
mumps virus a virus of the genus Rubulavirus that causes mumps and sometimes tenderness and swelling of the testes, pancreas, ovaries, or other organs.
naked virus , nonenveloped virus a virus lacking an outer lipoprotein bilayer.
neurotropic virus one that has a predilection for and causes infection in nervous tissues, e.g., the rabies virus.
Norwalk virus a calicivirus that is a common agent of epidemics of acute gastroenteritis.
oncogenic viruses an epidemiologic class of viruses that are acquired by close contact or injection and cause usually persistent infection; they may induce cell transformation and malignancy.
Oropouche virus a virus of the genus Bunyavirus that causes illness in Brazil; infection is characterized by fever, chills, malaise, headache, myalgia, and arthralgia, sometimes nausea and vomiting, and occasionally central nervous system involvement.
orphan viruses viruses isolated in tissue culture but not found specifically associated with any illness.
papilloma virus papillomavirus.
parainfluenza virus a group of viruses of the family Paramyxoviridae that cause upper respiratory tract disease in humans and other animals.
paravaccinia virus pseudocowpox v.
Powassan virus a tickborne virus of the genus Flavivirus that causes encephalitis in the eastern United States and Canada.
pox virus poxvirus.
pseudocowpox virus a virus of the genus Parapoxvirus that produces nodular lesions similar to those of cowpox and orf on the udders and teats of milk cows and the oral mucosa of suckling calves (paravaccinia), which can be transmitted to humans during milking.
Puumala virus see Hantavirus.
rabies virus an RNA virus of the rhabdovirus group that causes rabies.
rabies-like viruses Lyssavirus.
respiratory viruses an epidemiologic class of viruses that are acquired by inhalation of fomites and replicate in the respiratory tract, causing local rather than generalized infection; they are included in the families Adenoviridae, Coronaviridae, Orthomyxoviridae, Paramyxoviridae, and Picornaviridae.
respiratory syncytial viruses (RSV) viruses belonging to the genus Pneumovirus, causing respiratory disease that is particularly severe in infants, and in tissue causing syncytium formation.
RNA virus one whose genome consists of RNA.
Rous-associated virus (RAV) a helper virus in whose presence a defective Rous sarcoma virus is able to form a protein coat.
Rous sarcoma virus (RSV) see Rous sarcoma, under sarcoma .
rubella virus the sole species of the genus Rubivirus, the etiologic agent of rubella.
St. Louis encephalitis virus a virus of the genus Flavivirus, that is the etiologic agent of St. Louis encephalitis; transmitted by mosquitoes.
sandfly fever viruses Phlebovirus.
satellite virus a strain of virus unable to replicate except in the presence of helper virus; considered to be deficient in coding for capsid formation.
Seoul virus see Hantavirus.
simian immunodeficiency virus (SIV) a virus of the genus Lentivirus, closely related to human immunodeficiency virus, that causes inapparent infection in African green monkeys and a disease resembling acquired immunodeficiency syndrome in macaques.
Sin Nombre virus a virus of the genus Hantavirus that causes hantavirus pulmonary syndrome in the western United States.
slow virus any virus causing a disease characterized by a long preclinical course and gradual progression once the symptoms appear.
street virus virus from a naturally infected animal, as opposed to a laboratory-adapted strain of the virus.
tanapox virus a virus of the genus Yatapoxvirus that is the etiologic agent of tanapox.
Toscana virus a virus of the Naples serogroup of the genus Phlebovirus, an etiologic agent of phlebotomus fever.
varicella-zoster virus human herpesvirus 3
variola virus the virtually extinct virus, belonging to the genus Orthopoxvirus, that is the etiologic agent of smallpox. No natural infection has occurred since 1977 and no reservoir of the virus now exists.
VEE virus , Venezuelan equine encephalomyelitis virus see equine encephalomyelitis v.
WEE virus , western equine encephalomyelitis virus see equine encephalomyelitis v.
West Nile virus a virus of the genus Flavivirus that causes West Nile encephalitis; it is transmitted by Culex mosquitoes, with wild birds serving as the reservoir.
Yaba monkey tumor virus a virus of the genus Yatapoxvirus that is the etiologic agent of yabapox.
yellow fever virus a mosquito-borne species of the genus Flavivirus that causes yellow fever in Central and South America and Africa.
na·ked virus (n  k d)n. A virus without an enclosing envelope, consisting only of a nucleocapsid. |
naked virus
A non-enveloped virus–eg, a reovirus
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