orphan virus

orphan virus

n.

Any of various viruses, such as enteric orphan viruses, that may not be specifically associated with disease but may exhibit pathogenicity.

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orphan virus

Etymology: Gk, orphanos, without parents; L, virus, poison

a virus that has been isolated and identified, although it has not been associated with any particular disease.

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orphan

a newborn animal without a dam.

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orphan virus

usually enteroviruses, that have no known disease attributed to them.

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virus

any member of a unique class of infectious agents, which were originally distinguished by their smallness (hence, they were described as 'filtrable' because of their ability to pass through bacteria-retaining filters) and their inability to replicate outside of a living host cell; because these properties are shared by certain bacteria (rickettsiae, chlamydiae), viruses are further characterized by their simple organization and their unique mode of replication. A virus consists of genetic material, which may be either DNA or RNA, and is surrounded by a protein coat and, in some viruses, by a membranous envelope.

For a list of animal viruses and their classification see Table 8.1.

Unlike cellular organisms, viruses do not contain all the biochemical mechanisms for their own replication; viruses replicate by using the biochemical mechanisms of a host cell to synthesize and assemble their separate components. When a complete virus particle (virion) comes in contact with a host cell, the viral nucleic acid and, in some viruses, a few enzymes are introduced into the host cell.

Viruses vary in their stability; some such as poxviruses, parvoviruses and rotaviruses are very stable and survive well outside the body while others, particularly those viruses that are enveloped, such as herpesvirus, influenza virus, do not survive well and therefore usually require close contact for transmission and are readily destroyed by disinfectants, particularly those with a detergent action. Some viruses produce acute disease while others, sometimes referred to as slow viruses, such as retroviruses and lentiviruses and the scrapie agent, produce diseases which progress often to death over many years. Viruses in several families are transmitted by arthropod vectors.

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virus amplification

see replication.

arbor virus

an incorrect, obsolete term for arbovirus.

attenuated virus

one whose pathogenicity has been reduced by serial animal passage or other means. See also attenuation (2).

avianized virus

see avianized.

bacterial virus

one that is capable of producing transmissible lysis of bacteria. See also bacteriophage.

C-type virus

see c-type virus.

Coxsackie virus

coxsackievirus.

defective virus

one that cannot be completely replicated or cannot form a protein coat or envelope; in some cases replication can proceed if missing gene functions are supplied by other viruses, termed helper virus (see below).

ECHO virus

see echovirus.

enteric virus

see enterovirus.

enteric orphan v's

orphan viruses isolated from the intestinal tract but not known to cause disease, hence orphan.

feline sarcoma virus

see feline sarcoma virus.

filterable virus, filtrable virus

a pathogenic agent capable of passing through fine filters able to exclude bacteria; outdated terminology.

fixed virus, virus fixé

rabies virus whose virulence and incubation period have been stabilized by serial passage and have remained fixed during further transmission; used for inoculating animals from which rabies vaccine is prepared.

foaming virus

feline syncytia-forming virus (FeSFV). So called because it causes foamy degeneration in feline cell cultures.

helper virus

one that aids in the development of a defective virus by supplying or restoring the activity of the viral gene such as that forming the protein coat.

herpes virus

herpesvirus.

human hepatitis virus

infection of chimpanzees with some of the human hepatitis viruses can result in infection of human workers.

influenza virus

any of a group of orthomyxoviruses that causes influenza. See influenza.

latent virus

a noninfective state and is demonstrable by indirect methods that activate it.

lytic virus

one that is replicated in the host cell and causes death and lysis of the cell.

masked virus

latent virus.

virus N

a type A influenza virus found in birds.

virus neutralization

see neutralization tests.

occult virus

see occult virus.

orphan virus

see orphan virus.

parainfluenza virus

see parainfluenzavirus.

pox virus

see pox.

rabies virus

an RNA virus of the rhabdovirus group that causes rabies.

respiratory syncytial virus

see paramyxoviridae.

slow virus

the name given to certain viruses that cause diseases characterized by a long incubation period and a very prolonged clinical course, e.g. the lentiviruses of sheep, maedi and visna.

street virus

rabies virus from a naturally infected animal, as opposed to a laboratory-adapted, fixed virus.