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Virology

Virology is the study of viruses – submicroscopic, parasitic particles of genetic material contained in a protein coat – and virus-like agents. It focuses on the following aspects of viruses: their structure, classification and evolution, their ways to infect and exploit host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy. Virology is considered to be a subfield of microbiology or of medicine. Virology is the study of viruses – submicroscopic, parasitic particles of genetic material contained in a protein coat – and virus-like agents. It focuses on the following aspects of viruses: their structure, classification and evolution, their ways to infect and exploit host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy. Virology is considered to be a subfield of microbiology or of medicine. A major branch of virology is virus classification. Viruses can be classified according to the host cell they infect: animal viruses, plant viruses, fungal viruses, and bacteriophages (viruses infecting bacterium, which include the most complex viruses). Another classification uses the geometrical shape of their capsid (often a helix or an icosahedron) or the virus's structure (e.g. presence or absence of a lipid envelope). Viruses range in size from about 30 nm to about 450 nm, which means that most of them cannot be seen with light microscopes. The shape and structure of viruses has been studied by electron microscopy, NMR spectroscopy, and X-ray crystallography. The most useful and most widely used classification system distinguishes viruses according to the type of nucleic acid they use as genetic material and the viral replication method they employ to coax host cells into producing more viruses: The latest report by the International Committee on Taxonomy of Viruses (2005) lists 5450 viruses, organized in over 2,000 species, 287 genera, 73 families and 3 orders. Virologists also study subviral particles, infectious entities notably smaller and simpler than viruses: Taxa in virology are not necessarily monophyletic, as the evolutionary relationships of the various virus groups remain unclear. Three hypotheses regarding their origin exist: Of particular interest here is mimivirus, a giant virus that infects amoebae and encodes much of the molecular machinery traditionally associated with bacteria. Is it a simplified version of a parasitic prokaryote, or did it originate as a simpler virus that acquired genes from its host? The evolution of viruses, which often occurs in concert with the evolution of their hosts, is studied in the field of viral evolution. While viruses reproduce and evolve, they do not engage in metabolism, do not move, and depend on a host cell for reproduction. The often-debated question of whether they are alive or not is a matter of definition that does not affect the biological reality of viruses.

[ "Medicine", "Biology", "Trypanosomidae", "Tropical ulcer", "Equine coronaviruses", "Spirochaetae", "La Crosse virus encephalitis" ]
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