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.
Some microbiologists classify viruses as microorganisms, while others don't because they are "nonliving" and describe viruses as microscopic infective agents.
Viruses are unique microorganisms 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 that 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".
What are "friendly" viruses?
Most of us know about friendly bacteria that exists in our intestines and help us digest food. Scientists from San Diego State University reported in the Proceedings of the National Academy of Sciences (May 2013 issue) that humans also carry friendly viruses that help protect us from dangerous bacteria, including E. coli.
Jeremy Barr and team believe their discovery may change how several diseases are treated. They discovered that mucus contains bacteriophages, viruses that actively protect their hosts form harmful bacteria by destroying them.
Barr wrote "Taking previous research into consideration, we are able to propose the Bacteriophage Adherence to Mucus -- or BAM -- is a new model of immunity, which emphasizes the important role bacteriophage play in protecting the body from invading pathogens. . . . . We envision BAM influencing the prevention and treatment of mucosal infections seen in the gut and lungs, having applications for phage therapy and even directly interacting with the human immune system."
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:
- The common cold
- Human papilloma virus
- Hanta fever
- HIV (the virus that causes AIDS)
- Cold sores
- SARS (Severe acute respiratory syndrome)
- 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.