virus defined in 1951 yearvirus - virus;
virus - A member of a group of sub-microscopic agents that infect plants and animals, usually manifesting their presence by causing disease, and are unable to multiply outside the host tissues. Also attack bacteria (such a virus is a Bacteriophage). The fully formed, mature, virus (or virion) consists of nucleic acid within a protein or protein and lipid coat. Nucleic acid is either DNA or RNA in animal viruses, RNA in plant viruses and DNA (and occasionally RNA) in bacteriophages. Infectivity resides in nucleic acid component, which is released from the virion into the infected cell, where it initiates synthesis of more virions. A few kinds of virion contain enzyme(s) involved in penetration of host cell. Of great agricultural and medical importance, causing, e.g. various diseases of potato, cereals; foot-and-mouth disease, common cold, influenza, poliomyelitis, small pox, measles, yellow fever. In plants mainly found in Angiosperms, but attack the cultivated mushroom, and have been isolated from a few other fungi; attack wild and domestic mammals, birds and insects, as well as man. Some virus infected plants are prized as ornamentals, e.g. certain tulips, variegated Abutilon. Some viruses, artificially introduced, are used as agents of biological control, e.g. polyhedral viruses attacking leaf eating insect larvae in forests; myxomatosis virus killing rabbits.
Viruses are transmitted from plant to plant mostly by insects, aphids being most common vectors. Some soil-borne viruses are transmitted by eelworms and a few by soil-borne phycomycete fungus root parasites, e.g. Olpidium. Other viruses are spread by plant to plant contact. Viruses that are systemic in plants are spread very effectively by vegetative propagation, in tubers, bulbs, runners, etc. Few viruses are seed-borne. Animal viruses are spread by insect vectors, by contact, or in droplets of mucus expelled from nose, throat and mouth of infected animal and inhaled by another. There has been much argument as to whether viruses are living or not. The fact is that they have some of the properties of obviously living things, and not others. Whether they are called living or nonliving adds nothing to our understanding of their properties. Some viruses have been obtained in crystalline form. Different viruses are of varying grades of complexity; those that are roughly spherical are between 150 and 1300 Angstroms in diameter.
near virus in Knolik
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