What is Virology
Virology is the branch of pathology that deals with diseases caused by viruses, and their diagnoses. The viruses are very small particles that are not seen by Light Microscopes, the Electron Microscope is needed to see them. They are very small in size and can pass through filters. These do not have any metabolic activity and are not living organisms. There is no process of mitosis or meiosis in the viruses, they rather replicate. After entering inside the cell, the viral genetic material (DNA/RNA) utilizes the host cells metabolic machinery for viral replication.
Viruses may be planted viruses or animal viruses. Animal Viruses affect animals, including man. Certain viruses are specific to mankind. The field of medical virology deals strictly with those viruses, which cause disease in mankind. Certain viruses like that of Yellow Fever, Tick-Borne Encephalitis, Lassa Fever and Congo Crimean Haemorrhagic Fever (CCHF) are transmitted to human beings from infected animals. These viral conditions are called zoonosis.Types of viruses
Viruses differ from each other as far as their hosts are concerned. There are certain viruses like the poliovirus, which can only infect human beings. Other viruses, like the Rabies Virus, can infect many types of animals. The viruses like those of Yellow Fever and Japanese B Encephalitis are propagated in mosquitoes as well as warmblooded animals. They are also called Arboviruses (Arthropod-borne viruses).
The host range is determined by the presence of receptors on the surface of the cells of animals, to which a virus may attach in a peculiar cellular environment. The receptors are normal constituents of the cell membrane but the viruses utilize them for their own convenience. A CD-4 receptor for Human Immunodeficiency Virus (HIV) is a well-known example. The poliovirus affects the intestine and certain neuronal cells. On the other hand, the Mumps virus affects many types of cells like those of the heart, pancreas, thyroid, thymus, ovary, testis and brain, in addition to the cells of the salivary glands. The presence of a receptor on its surface, as well as the internal environment of the cell determines the potential for the infection of the cell with a particular virus.
Nomenclature
Viruses are named differently. Certain viruses are known by the names of the diseases they cause. Examples are the Rabies virus, Mumps virus, Poliovirus, various Hepatitis viruses (A to E), the Measles virus and the Yellow Fever virus. Certain viruses are named after their discoverers like Epstein Barr virus and Dane Particles. Certain viruses are given the name of the city or country of their original discovery like Coxsackie A and B viruses, West Nile virus, Japanese B Encephalitis and the Hazara virus. Certain viruses are named after the CPE that they cause, like Respiratory Syncytial virus or Cytomegalovirus. In some cases, more than one characteristic is combined, as in the Enterocytopathogenic Human Orphan viruses (Echoviruses). The name of a virus is now given by The International Committee of Viral Taxonomy.
Classification
The classification of viruses is complex. They are classified on the basis of the type of their genetic material i.e., DNA or RNA, the presence or absence of an envelope, their shape and characteristics of their genome and the enzymes present in them. Important groups are Herpesviruses, Orthomyxoviruses, Paramyxoviruses, Enteroviruses, Togaviruses, Retroviruses, Papovaviruses, Parvoviruses, and Poxviruses.
