virus
The definitions used in this glossary of terminology either have been provided by the authors of the articles, or have been extracted wholly or in part, or paraphrased from the following sources: The American Medical Association Encyclopedia of Medicine, Charles B. Clayman, MD, Medical Editor, Random House, New York, 1989; Biotechnology from A to Z, 2d Edition, William Bains, Oxford University Press, New York, New York, 2002; A Dictionary of Genetics, 6th Edition, Robert C. King and William D. Stansfield, Oxford University Press, New York, New York, 2002; Dorland's Illustrated Medical Dictionary, 29th and 30th Editions, W. B. Saunders Company, Philadelphia, 2000, 2003; Genes VII, Benjamin Lewin, Oxford University Press, New York, New York, 2000; The Gale Encyclopedia of Genetic Disorders, Volumes I and II, Stacey L. Blachford, Ed., Thomson Learning, New York, New York, 2002; The Merriam-Webster Dictionary, Merriam-Webster, Inc., Springfield, Massachusetts, 1997; Molecular Biology of the Cell, 3rd Edition, Bruce Alberts, et al., Garland Publishing, 1994; The Random House Dictionary of the English Language, Unabridged Edition, 1966; Webster's Ninth New Collegiate Dictionary, 1991.
DEFINITION:
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The smallest known type of infectious agent. Viruses are about one half to one hundredth the size of the smallest bacteria, from which they differ in having a much simpler structure and method of multiplication. Viral infections range from the trivial and harmless, such as warts, the common cold, and other minor respiratory tract infections, to extremely serious diseases, such as rabies, AIDS, and probably some types of cancer.
It is debatable whether viruses are truly living organisms or just collections of large molecules capable of self-replication under very specific favorable conditions. Their sole activity is to invade the cells of organisms, which they take over to make copies of themselves. Outside living cells, viruses are wholly inert. They are incapable of activities typical of life, such as metabolism (internal processing of nutrients).
The number of different kinds of virus probably exceeds the number of types of all other organisms. They parasitize all recognized life-forms---mammals, birds, reptiles, insects, plants, algae, even bacteria. Viruses are customarily separated into three subgroups on the basis of host specificity, namely bacterial viruses, animal viruses, and plant viruses. They are also classified as to their origin (e.g., reoviruses), mode of transmission (arboviruses, tickborne viruses), or the manifestations they produce (polioviruses, polyomaviruses, poxviruses). Not all viruses cause disease, but many do.
Used in 2 Article translations
Used in 2 Article translations