Virus

A virus is an ultramicroscopic infectious agent that only replicates within the cells of living hosts, generally animals, bacteria, and plants.http://dictionary.webmd.com/terms/virus Unlike a cell, a virus is unable to grow, eat, and reproduce on its own, and is only around one-millionth of an inch in size.http://dictionary.webmd.com/terms/virus

A virion, or virus particle, is composed of: a DNA or RNA core, that provides a specific set of genetic instructions; a coat of protein designed to protect the core; and in more complex viruses, a lipid membrane that envelopes the protein coat.http://www.medterms.com/script/main/art.asp?articlekey=5997 The shape and complexity of a virus can vary greatly.

Depending on the type, it is possible for a virus to survive for an extended period of time, years or more, outside of a host cell. Further, viruses are able to lay dormant within the genetic instructions of its host cell for long periods of time.http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/viruses/viruses.htm

The mechanism by which a virus spreads depends on the particular type, and include: transmission through the air, carrier organisms, surfaces that bodily fluids have come into contact with, and direct contact with body fluids like blood, nasal mucus, saliva, semen, sweat, and vaginal secretions.http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/viruses/viruses.htm In order to reduce the spread of viruses, it is important that infected individuals cover their cough and sneezes, wash their hands frequently, and that contact with bodily fluids is avoided.

Once an virus comes into contact with an individual, they find a host cell to infect, and begin to infect the individual through a process called the lytic cyclehttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/viruses/viruses.htm In the lytic cycle, a virion attaches to a host cell. Next, the virion releases its genetic instructions into the host cell. This genetic material then picks up the enzymes of the host cell. These enzymes then create the necessary parts for more virus particles. The parts are then assembled into new viruses, and break free from the host cell. The protein coating on the virus particles is responsible for seeking out the right host cells, and then attaching the virus to the membrane of that host cell.http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20lectures/viruses/viruses.htm

Some common infectious viruses include:

• AIDS
• Common cold
• Colorado tick fever
• Dengue fever
• Ebola
• Flu (Influenza)
• Hepatitis
• Herpes simplex
• Herpes zoster
• HPV
• Measles
• Mononucleosis
• Mumps
• Rabies
• Rubella
• SARS
• Varicella (Chickenpox)
• Variola (Smallpox)
• Viral Encephalitis
• Viral Gastroenteritis
• Viral Meningitis
• Viral Pneumonia
• West Nile disease
• Yellow feverhttp://www.mayoclinic.com/health/germs/ID00002