One of the most common causes of infection is a virus. Viruses consist mostly of nucleic acid and therefore have to enter living cells in order to reproduce. Common virus families include the rhinovirus which causes the common colds, hepatitis, herpes, and human immunodeficiency virus or HIV. Usually, a virus is not destructive but once it enters a living organism, it proliferates and cause damage to cells. Infection occurs when viruses invade and succeed to replicate inside the body. Viral infection can be called local or systemic.

A local viral infection is limited to the definite part of the body where the viruses remain. If the viruses also attack other different parts of the body, it is said to be a systemic viral infection. There is also acute viral infection or chronic viral infection. Acute viral infection, generally, looks as if it suddenly appears or last a short time. A chronic viral infection on the other hand, may take place slowly, over a long period of time and last for months or years. Another type of viral infection is the hospital-acquired viral infection or the so-called nosocomial viral infection. Nosocomial viral infection can either increase during a patient’s stay in the hospital or any health care facility. Doctors, nurses, and other allied health professionals can also acquire nosocomial viral infection while working in a health care facility and can cause major illness and time missing from work.

The most ordinary infection sites in the body are open wounds, blood, urinary tract, and respiratory tract. According to studies, frequent washing of hands is important to diminish the incidence of nosocomial viral infections. Chain of viral infection also applies to all pathogenic microorganisms or disease-causing microorganisms. In science, there are six links in the chain of viral infection. These are the etiologic agent, reservoir, portal of exit from the reservoir, a method of transmission, a portal of entry into a susceptible host, and the susceptible host itself. The etiologic agent is any microorganism such as viruses that causes a sickness. The reservoir is the habitat of the viruses. Some viruses do not harm people directly. They, sometimes, are just suspended in the air. The portal of exit from the reservoir is needed before a virus attack its target body cells.

The common human reservoirs of viruses are respiratory tract for flu virus, gastrointestinal tract for Hepatitis A virus, reproductive tract for Herpes Simplex Virus Type 2, and open wounds for human immunodeficiency virus or HIV by needle puncture, or skin breakdown. The method of transmission of viruses can be an indirect transmission, direct transmission or airborne transmission. The portal of entry of viruses into humans is usually through a breakdown in the skin. The susceptible host is a person who is at risk of having an illness caused by the virus or other pathogens. Viral infection can be prevented if the people know how to break the chain of infection. Breaking the chain of infection is easy; just break the chain by putting a barrier in any of the six links.

Read fever viral or bacterial with Viral Fever and viral infections without fever for more details