An infectious virus is a small infectious parasite that invades and replicates within the cells of other organisms, usually causing great harm. The term "infectious" specifically applies to things that colonize host cells and cause the host organism some level of harm. In most cases, a common infectious virus, such as the common cold, can be fought off by the host organism's immune system. Some viruses, however, can be extremely harmful, even deadly.
The mechanism by which an infectious virus reproduces is what causes harm to the host organisms. Viruses reproduce by overtaking the cells of host organisms and altering the genetic information within. The alterations cause the cell to produce more viral agents until the cell is full, at which point it bursts and the viruses spread to other cells. The process repeats as the viruses infect other cells, cause them to produce more viral cells and burst, and continue spreading. Unless the organism's immune system can defeat it, the infectious virus will usually kill the creature in the long run.
An infectious virus is made up of several parts. Most importantly, it has a store of nucleic acid, which is the genetic information it uses to overtake host cells and reprogram them to produce more viruses. This store of nucleic acid is stored within a protein coat that serves to protect it. Many viruses also contain some structure that allows them to puncture the membrane of a cell and insert the nucleic acid, thereby infecting the cell.
Scientists have long debated whether or not an infectious virus should be considered a living organism. While viruses do adapt to their environments and do try to reproduce on as large a scale as possible, they are not composed of cells. Only structures that are made up of cells are generally considered by the scientific community to be living things.
Viruses can be very harmful to human life, so health professionals and others take great care to try to reduce their spread. An infectious virus can spread through a variety of means, such as physical contact and fluid transfer. Some viruses can be transferred between organisms; mosquitoes have been known to carry viruses that eventually can infect people after the mosquito bites. To stop the spread of viruses, people generally try to clean their hands and cover their sneezes, preventing physical spread or spread through fluid transfer. Sometimes, people will, through chemical use or removal of breeding areas, try to prevent the reproduction of organisms that carry viruses.
