What Is A Virus? What Is A Viral Infection?

Editor's Choice
Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: Biology / Biochemistry;  Flu / Cold / SARS;  Swine Flu
Article Date: 20 Jul 2009 - 1:00 PDT

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A virus (from the Latin virus meaning toxin or poison) is a microscopic organism consisting of genetic material (RNA or DNA) surrounded by a protein, lipid (fat), or glycoprotein coat. Viruses are unique organisms because they cannot reproduce without a host cell. After contacting a host cell, a virus will insert genetic material into the host and take over the host's functions. The cell, now infected, continues to reproduce, but it reproduces more viral protein and genetic material instead of its usual products. It is this process that earns viruses the classification of "parasite".

How are viruses spread?

Viruses may spread vertically (from mother to child) or horizontally (from person to person). A virus's ability to spread depends on the makeup of the virus.

Some viruses can spread by simple contact, exchanges of saliva, coughing, or sneezing. Some require sexual contact, while others go through the fecal-oral route via contaminated food or water. Still other viruses require an insect like a mosquito to carry the virus from person to person.

What diseases are caused by viruses?

Several human diseases are caused by viruses. These include:

• Smallpox
• The common cold
• Measles
• Chickenpox
• Hepatitis
• Influenza
• Human papilloma virus
• Shingles
• Herpes
• Polio
• Rabies
• Ebola
• Hanta fever
• HIV (the virus that causes AIDS)
• Cold sores
• SARS (Severe acute respiratory syndrome)
• Dengue
• Epstein-Barr virus
• Some types of cancer

How do we fight viruses?

When the body's immune system detects a viral infection, it begins to respond in a generic way. A process begins called RNA interference, which is crucial to fighting viruses because it degrades the viral genetic material and enables cells to survive the infection. The immune system also produces specific antibodies that are capable of binding to viruses and making them non-infectious. In addition, the body's T cells are sent to destroy the virus.

Although most viral infections result in a protective response from the immune system, viruses such as HIV specialize in evading the immune system by using a number of different techniques. Neurotropic viruses are also very capable of avoiding our natural immune system's response to infection.

How are viruses prevented and treated?

Whereas bacterial infections can be treated with antibiotics, viral infections require either vaccinations to prevent them or antiviral drugs to treat them.

Vaccinations are generally the cheapest and most effect way to prevent viruses. Currently, vaccinations exist for polio, measles, mumps, rubella, and smallpox among others. In fact, vaccinations have been instrumental in eliminating diseases such as smallpox and reducing other viral diseases to extremely rare status. Virus vaccinations consist of a weakened form of the virus (live-attenuated viruses) or viral proteins called antigens. Live-attenuated vaccines carry the risk causing the original disease in people with weak immune systems.

Antiviral drugs have been developed largely in response to the AIDS pandemic. These drugs do not destroy the pathogen but instead inhibit their development. Antiviral medications are relatively harmless to the host.

Written by Peter Crosta M.A.
Copyright: Medical News Today
Not to be reproduced without permission of Medical News Today