infections
Overview of Viral Infections
Introduction
A virus is composed of nucleic acid, either Genes , surrounded by a protein coat. It requires a living cell in which to multiply. A viral infection can lead to a spectrum of symptoms from asymptomatic (no overt symptoms) to severe disease. People may get viruses by swallowing or inhaling them, by being bitten by insects, through sexual contact, or congenitally (passed by a pregnant person to the fetus). Most commonly, viral infections involve the nose, throat, and upper airways, or systems such as the nervous, gastrointestinal, and reproductive systems. Doctors may base the diagnosis on symptoms, blood tests and cultures, or examination of infected tissues. Antiviral drugs may interfere with the reproduction of viruses or strengthen the immune response to the viral infection. A virus is a small infectious organism—much smaller than a fungus or bacterium—that must invade a living cell to reproduce (replicate). The virus attaches to a cell (called the host cell), enters the cell, and releases its Genes inside the cell. The virus’s DNA or RNA is the genetic material containing the information needed to replicate the virus. The virus’s genetic material takes control of the host cell and forces it to replicate the virus. The infected cell usually dies because the virus keeps it from performing its normal functions. When the infected host cell dies, it releases new viruses, which go on to infect other cells. Viruses are classified as DNA viruses or RNA viruses, depending on whether they use DNA or RNA to replicate. DNA viruses include Overview of Herpesvirus Infections . RNA viruses include Some viruses do not kill the cells they infect but instead alter the cell's functions. Sometimes the infected cell loses control over normal cell division and becomes cancerous. Some viruses, such as Hepatitis B, Chronic and A virus takes control of the cell it infects and causes it to make more viruses. Viruses usually infect one particular type of cell. For example, Common Cold infect only cells of the upper respiratory tract. Additionally, most viruses infect only a few species of plants or animals. Some infect only people. Many viruses commonly cause and older adults. 