virus
Viruses are infectious pathogens smaller in size than bacteria. It consists of RNA, a genetic material, and proteins surrounding the genetic material, and very few viruses have DNA. The word virus comes from the Latin word "virus", which means poison. The size is small enough to pass through the bacterial filter and is usually between 10 and 1000 nm. Because it can not metabolize itself, it penetrates its own DNA or RNA into the host cell, replicates its own genetic material using the invaded cell organelles, and produces viruses like oneself. In this process, host cells are damaged or destroyed, causing disease in the host. Some hosts, however, do not cause disease when infected with the virus, and they sometimes act as a viral mediator.