Defionition of virus

The names of subfamilies end in -virinae. Vernacular names continue to be used to describe the viruses within a genus. In this text, Latinized endings for families and subfamilies usually are not used. Table shows the current classification of medically significant viruses.

In the early days of virology, viruses were named according to common pathogenic properties, e. From the early s until the mids, when many new viruses were being discovered, it was popular to compose virus names by using sigla abbreviations derived from a few or initial letters. Thus the name Picornaviridae is derived from pico small and RNA; the name Reoviridae is derived from respiratory, enteric, and orphan viruses because the agents were found in both respiratory and enteric specimens and were not related to other classified viruses; Papovaviridae is from papilloma, polyoma, and vacuolating agent simian virus 40 [SV40] ; retrovirus is from reverse transcriptase; Hepadnaviridae is from the replication of the virus in hepatocytes and their DNA genomes, as seen in hepatitis B virus.

Hepatitis A virus is classified now in the family Picornaviridae, genus Hepatovirus. Although the current rules for nomenclature do not prohibit the introduction of new sigla, they require that the siglum be meaningful to workers in the field and be recognized by international study groups.

Several viruses of medical importance still remain unclassified. Some are difficult or impossible to propagate in standard laboratory host systems and thus cannot be obtained in sufficient quantity to permit more precise characterization. Hepatitis E virus, the Norwalk virus and similar agents see Ch.

The fatal transmissible dementias in humans and other animals scrapie in sheep and goat; bovine spongiform encephalopathy in cattle, transmissible mink encephalopathy; Kuru, Creutzfeldt-Jakob disease, and Gerstmann-Straussler-Scheinker syndrome in humans see Ch. The agents causing transmissible subacute spongiform encephalopathies have been linked to viroids or virinos i.

Some of the transmissible amyloidoses show a familial pattern and can be explained by defined mutations which render a primary soluble glycoprotein insoluble, which in turn leads to the pathognomonic accumulation of amyloid fibers and plaques. The pathogenesis of the sporadic amyloidoses, however, is still a matter of highly ambitious research. Turn recording back on. National Center for Biotechnology Information , U. Show details Baron S, editor. Search term. General Concepts Structure and Function Viruses are small obligate intracellular parasites, which by definition contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat.

Classification of Viruses Morphology: Viruses are grouped on the basis of size and shape, chemical composition and structure of the genome, and mode of replication. Nomenclature Aside from physical data, genome structure and mode of replication are criteria applied in the classification and nomenclature of viruses, including the chemical composition and configuration of the nucleic acid, whether the genome is monopartite or multipartite.

Structure and Function Viruses are inert outside the host cell. Classification of Viruses Viruses are classified on the basis of morphology, chemical composition, and mode of replication.

Morphology Helical Symmetry In the replication of viruses with helical symmetry, identical protein subunits protomers self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path. Figure The helical structure of the rigid tobacco mosaic virus rod. Figure Fragments of flexible helical nucleocapsids NC of Sendai virus, a paramyxovirus, are seen either within the protective envelope E or free, after rupture of the envelope.

Icosahedral Symmetry An icosahedron is a polyhedron having 20 equilateral triangular faces and 12 vertices Fig. Figure Icosahedral models seen, left to right, on fivefold, threefold, and twofold axes of rotational symmetry.

Figure Adenovirus after negative stain electron microscopy. Virus Core Structure Except in helical nucleocapsids, little is known about the packaging or organization of the viral genome within the core. Figure Two-dimensional diagram of HIV-1 correlating immuno- electron microscopic findings with the recent nomenclature for the structural components in a 2-letter code and with the molecular weights of the virus structural glyco- proteins.

Figure Schemes of 21 virus families infecting humans showing a number of distinctive criteria: presence of an envelope or double- capsid and internal nucleic acid genome. Virus Classification On the basis of shared properties viruses are grouped at different hierarchical levels of order, family, subfamily, genus and species. JB Lippincott, Philadelphia, Gajdusek DC. Unconventional viruses and the origin and disappearance of kuru.

Gelderblom HR. Assembly and morphology of HIV: potential effect of structure on viral function. Mattern CFT: Symmetry in virus architecture. Marcel Dekker, New York, Raven Press, New York, Springer-Verlag, New York, Elsevier, Amsterdam, Structure and Classification of Viruses. In: Baron S, editor. Chapter In this Page. Related information. PubMed Links to PubMed. Similar articles in PubMed. Review Retroviral Virions and Genomes [Retroviruses.

Review Molecular mechanisms of virus spread and virion components as tools of virulence. A review. Acta Microbiol Immunol Hung. Review First glimpses at structure-function relationships of the nucleocapsid protein of retroviruses. J Mol Biol. Packaging of a unit-length viral genome: the role of nucleotides and the gpD decoration protein in stable nucleocapsid assembly in bacteriophage lambda. Epub Sep 3. Save Word. Definition of coronavirus. Examples of coronavirus in a Sentence Recent Examples on the Web Suu Kyi was also sentenced to two years for violating the natural disaster management law, which regards breaking coronavirus rules.

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From the Editors at Merriam-Webster. Coronavirus and the New Words We Added Style: MLA. Medical Definition of coronavirus. More from Merriam-Webster on coronavirus Britannica. Buying Guide Our team at The Usage has selected the best antivirus software. Learn More About virus. Time Traveler for virus The first known use of virus was in See more words from the same year. From the Editors at Merriam-Webster. Style: MLA.

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