Virology is the study of viruses, those troublesome microorganisms that can cause us harm as the causative agents of diseases such influenza and Human Immunodeficiency Virus (HIV). But on the flipside they also have positive uses in medicine, being used in immunisation and also in delivering new genes into an organism's genome to useful effect. Virology, which can be considered an area of microbiology, covers all aspects of the virus, from evolution, structure, life cycle, and function, to the diseases that they are responsible for and the host defences against them.
Viruses have an interesting internal structure and replication cycle that virologists are actively investigating. Viruses are infectious particles that are loaded with genetic material (DNA or RNA) and the machinery to insert themselves into host cells, splice themselves into the host genome and get themselves replicated. The various structures and all of the phases of the life cycle of the virus are potentially useful to the virologist both for classification and for inventing ways to destroy the virus or limit its damaging effects.
Classification, which is a major part of virology, can be done in several ways. One way is in terms of the host organisms that the virus infects, such as animals, plants, fungi, and bacteria. Each of these different types of cell is different so each presents a different challenge to the virus in its efforts to get replicated. This, in turn, provides a different set of challenges to those virologists attempting to study the virus. Viruses can also be classified in terms of the genetic material present. They may have, for example, a single or double strand of RNA or DNA.
Besides host organism and the type of genetic material, the shape of the virus is also used in classification. For instance, the protein capsid at the heart of the virus, which protects its genetic material, may be several different shapes. It may be helical, for example, or icosahedral (almost spherical). It may take a more complex form with tails or an envelope constructed from host cell membranes.
The key job of the virologist is to go beyond classification and to use all the knowledge of the virus and its activities and effects to discover ways to destroy it, prevent transmission of it, or at the very least to prevent its detrimental effects. More recently, the use of viruses in genetic engineering projects has widened the field. Now it is possible to modify a virus so that it splices a useful gene into the genome of a target organism's cells, allowing improvements in crops, for example.