A virus is an ultramicroscopic infectious organism that, having no independent metabolic activity, can replicate only within a cell of another host organism. A virus consists of a core of nucleic acid, either RNA or DNA, surrounded by a coating of antigenic protein and sometimes a lipid layer surrounds it as well. The virus provides the genetic code for replication, and the host cell provides the necessary energy and raw materials. There are more than 200 viruses that are know to cause disease in humans. …
