Overview of viral infections

[Mary Mallozziberg]

A virus is composed of nucleic acid, either DNA or RNA, 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, or through sexual contact.
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 DNA or RNA inside the cell. The virus’s DNA or RNA is the genetic material containing the information needed to make copies of (replicate) the virus. The virus’s genetic material takes control of the cell and forces it to replicate the virus. The infected cell usually dies because the virus keeps it from performing its normal functions. When it dies, the cell 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. RNA viruses include retroviruses, such as HIV (human immunodeficiency virus). RNA viruses, particularly retroviruses, are prone to mutate.
Some viruses do not kill the cells they infect but instead alter the cell