attenuation

1. The act of attenuating. 2. Diminution of virulence in a strain of an organism, obtained through selection of variants that occur naturally or through experimental means. 3. Loss of energy of a beam of radiant energy due to absorption, scattering, beam divergence, and other causes as the beam propagates through a medium. 4. Regulation of termination of transcription; involved in control of gene expression in specific tissues.

- interaural a. the reduction in intensity the head provides sound presented to one ear canal before it gets to the other ear; for air conduction, the reduction approximates 35 dB, but for bone conduction, it is only about 10 dB.

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at·ten·u·a·tion ə-.ten-yə-'wā-shən n a decrease in the pathogenicity or vitality of a microorganism or in the severity of a disease

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n.

reduction of the disease-producing ability (virulence) of a bacterium or virus by chemical treatment, heating, drying, by growing under adverse conditions, or by passing through another organism. Treated (attenuated) bacteria or viruses are used for many immunization.

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at·ten·u·a·tion (ə-ten″u-aґshən) [L. attenuatio, from ad- to + tenuis thin] 1. the act of thinning or weakening. 2. reduction in virulence of a pathogenic organism, usually by adaptation to another host or a different culture medium. 3. reduction in energy of a beam of radiation when it passes through tissue or other material. Cf. radiation absorption.