Viruses are infectious agents that are too small to be seen with a standard light microscope. They are obligate intracellular parasites which means they penetrate the host cells and basically program the cell to assemble new virus particles. Viral infections can cause disease in any part of the body. Pathogenic viruses infect the body through the respiratory tract, ingestion, insect bites, animal bites and sexual transmission among other routes.
Common Cold
This is probably the most common illness known. According to the National Institute of Allergy and Infectious Diseases, over the course of a year, people in the United States suffer from 1 billion colds. There are more than 200 different viruses that have been implicated in colds, with coronaviruses and adenoviruses being most common.
Influenza
Influenza, or flu, is a respiratory infection caused by several different flu viruses. Though the symptoms of flu overlap with those of a cold, there are several differences. For example, cold sufferers rarely get fevers or the extreme body aches that someone with the flu does. According to the U.S. Centers for Disease Control and Prevention (CDC), on average, 5 to 20 percent of the U.S. population gets the flu annually. More than 200,000 of those people are hospitalized from flu-related complications and about 36,000 people die from flu-related causes.
Varicella-Zoster
With this virus you get two diseases for the price of one. The same virus causes chickenpox (varicella) and shingles (zoster). Chickenpox is a highly contagious disease that causes skin lesions and usually occurs in children. Shingles is more of a sporadic disease that appears in older individuals most frequently. You must have had chickenpox before you can develop shingles. After a bout with chickenpox, the virus goes dormant in the nerve tissue. It can later reactivate and cause shingles, which can be quite painful and are typically found on one side of the body or face.
Human Papillomavirus
The human papillomaviruses (HPV) cause warts of all types. While there are many types of HPV, there are approximately 40 types that are transmitted through sexual contact. According to the CDC, there are approximately 20 million Americans who are currently infected with HPV. Another 6 million people become newly infected each year. HPV is so common that at least 50 percent of sexually active men and women get it at some point in their lives. Some types of HPV cause genital warts while other types have been implicated in cervical cancer
Herpes
There are two types of herpes simplex virus (HSV); type 1 is most commonly associated with cold sores or fever blisters, while type 2 is the usual cause of genital herpes. Both types of HSV can infect the genitals or the mouth. There is no treatment for the cure of herpes; however there are antiviral drugs which treat symptoms and shorten and prevent future outbreaks.
References
- "Health Matters," National Institute of Allergy and Infectious Diseases, 2004
- CDC- Human Papillomaviruses
- CDC-Herpes
