Viral Infections

There are more than 400 different viruses that are capable of infecting humans. Other viruses such as bacteriophages (viruses that infect bacteria), plant viruses and animal viruses also exist. There are many means by which a viral transmission can occur. For instance, they can be airborne viruses, arthropod-borne viruses, person-to-person transmitted viruses, food- and waterborne viruses, sexually transmitted viruses, and prions.

Infection occurs when a virus takes over the cell machinery and makes many copies of it. While the virus replicates, host cells are either destroyed or are reduced in their normal functional activity. The progeny that is released then continues the cycle by affecting other cells and multiplying to form more copies of the virus. It ultimately ends up destroying the host cells completely. A virus particle or virion can be made up of a single- or double-stranded DNA or RNA. Virions are obligate intracellular pathogens that absolutely require a host cell to reproduce. Thus, viruses work in a simple way and yet give rise to a range of diseases by means of genetic variation. This type of simplicity of viruses that leads to intense pathological features, clinical consequences and death is what makes virology (study of viruses) important.

A virus under magnification: A viral infection may be systemic or localized, depending upon the type of virus that infects the body.

Infection caused by virus can affect all types of body tissue. Symptoms for viral infections include headache, high fever, weakness, muscle pain, nausea, vomiting, diarrhea, and abdominal pain. Although there is no accurate treatment available for viral infections, physicians usually treat them with antibiotics. Antiviral drugs against some viruses are also available. A viral infection may be systemic (spread throughout the body) or localized (infect only at one location) depending upon the type of virus that infects.