1. Specifically, a term for a group of infectious agents that with few exceptions are capable of passing through fine filters that retain most bacteria, are usually not visible through the light microscope, lack independent metabolism, and are incapable of growth or reproduction apart from living cells. They have a prokaryotic genetic apparatus but differ sharply from bacteria in other respects. The complete particle usually contains either DNA or RNA, not both, and is usually covered by a protein shell or capsid that protects the nucleic acid. They range in size from 15 nm up to several hundred nm. Classification of viruses depends on physiochemical characteristics of virions as well as on mode of transmission, host range, symptomatology, and other factors.
Synonym(s):
ultravirus.
[L. poison]