A virus is a piece of genetic code included in an infecting protein or virus which invades healthy living cells and utilizes the host’s metabolic functions to create a new generation of viruses. This method of replicating themselves has been around for millions of years. However, the way they execute their replication process varies. Some simply insert their viral genetic material directly into the host’s genetic code, where it is able to sit dormant until it is translated at some later date.
Many viruses make use of their hosts cellular machinery to replicate themselves. In order to do this, they must hijack important DNA sequences or regulatory mechanisms within the cell. Once aboard the cell, they replicate rapidly using an artificial copying machine known as a transposon. Unfortunately, these viruses often damage the host cells and render them unable to utilize cellular machinery effectively, thus resulting in death of the infected cells.
Other viruses make use of the host’s own cellular machinery to replicate. Examples of these are the herpes simplex virus (HSV), shingles, Epstein-Barr virus (EBV), and the recently discovered West Nile virus (NNW). While all of these viruses can be dangerous, few are deadly. The best examples of fatal viruses are AIDS and the flu. Even small quantities of the infectious agent are enough to cause death.
However, many viruses utilize genetic information to infect and thus create copies of themselves. This information can either come from natural means, such as DNA or RNA, or from unnatural means, such as nucleic acid polymerase. Since most modern laboratory equipment makes it possible to detect and identify the genetic code, it has been useful for scientists to study many different viruses over the years. For instance, medical researchers have been able to sequence the genetic code of the swine flu virus, revealing the viral mechanisms of this pathogen. Likewise, sequencing the genetic material of the Human Immunodeficiency Virus has given scientists and medical researchers insight into the disease and potential treatments.
A capsid is a protein component found within the envelope that surrounds a virus’ nucleic acid core. While most viruses have a single capsid, some produce two, which means that they have two envelopes (one internal and one external to the human body). One of the primary structures found within the capsid is called the viral envelope viremia, which aids in the entry and spread of the virus throughout the body. Some viruses produce their own capsids, while others rely on natural capsid production from an uninfected individual.
The membrane of a virus is another membrane found between an active virus and its host cell (not a part of the cell itself). In effect, a virus’ replicated envelope releases a damaging payload onto the host cell that requires the cellular machinery (nucleic acid) to repair. If the cellular machinery cannot complete the repair, then the virus replicates once again, with the new (replicated) virus entering the body. The balance between infection and the progression of a virus determines the course of the virus and, consequently, the development of a pathogen.