Virology is the study of viruses. It is a subspecialty of microbiology. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archetypes. They replicate only inside the living cells of an organism and are submicroscopic infectious agents. They are found in almost every ecosystem on earth and are the most numerous type of biological entity.
When a cell gets infected, it rapidly produces thousands of identical copies of the original virus. When in the process of infecting a cell or not inside an infected cell, viruses exist in the form of independent particles, or virions.
The shapes range from simple helical and icosahedral forms to more complex structures. Most of the virus species have virions that are too small to be seen with an optical microscope as they are one hundredth the size of most bacteria.
The spread of the virus takes place in many ways. One of the ways of transmission is through disease-bearing organisms… Influenza viruses are spread by coughing and sneezing. Common causes of viral gastroenteritis, are transmitted by the fecal-oral route, passed by hand-to-mouth contact or in food or water by Norovirus and rotavirus. HIV is one of several viruses transmitted through sexual contact and by exposure to infected body fluids like blood and semen, and instruments like needles and scalpels.
They are acellular therefore the viral populations do not grow through cell division. Instead, they use the machinery and metabolism of a host cell to produce multiple copies of themselves, which they assemble in the cell. The host cell is forced to rapidly produce thousands of identical copies of the original virus when infected.