MSH: Minute infectious agents whose genomes are composed of DNA or RNA, but not both. They are characterized by a lack of independent metabolism and the inability to replicate outside living host cells.,CSP: group of minute infectious agents characterized by a lack of independent metabolism and by the ability to replicate only within living host cells; have capsid, may have DNA or RNA (not both).,NCI: In medicine, a very simple microorganism that infects cells and may cause disease. Because viruses can multiply only inside infected cells, they are not considered to be alive.,NCI: An infectious agent which consists of two parts, genetic material and a protein coat. These organisms lack independent metabolism, and they must infect the cells of other types of organisms to reproduce. Most viruses are capable of passing through fine filters that retain bacteria, and are not visible through a light microscope.