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With advent of virology, researchers have found several uses for these unique organisms. They have been used extensively in medicine and in genetic engineering. Some of the uses of viruses are outlined as follows.
Viruses have been used extensively in molecular and cellular biology studies. These viruses provide the advantage of being simple systems that can be used to manipulate and investigate the functions of cells.
Viruses have been used extensively in genetics research and understanding of the genes and DNA replication, transcription, RNA formation, translation, protein formation and basics of immunology.
Viruses are being used as vectors or carriers that take the required material for treatment of a disease to various target cells. They have been studied extensively in management of inherited diseases and genetic engineering as well as cancers.
These are highly specific viruses that can target, infect, and (if correctly selected) destroy pathogenic bacteria. Bacteriophages are believed to be the most numerous type of viruses accounting for the majority of the viruses present on Earth. These are basic tools in molecular biology. They have been researched for their use in therapy.
Nanotechnology deals with microscopic particles. These have various uses in biology and medicine and nanotechnology has been used in genetic engineering. Viruses can be used as carriers for genetically modified sequences of genomes to the host cells.
Viruses may be tiny but have the capacity to cause death and devastation to large populations in epidemics and pandemics. This has led to the concern that viruses could be used for biological warfare.
Modification and genetic engineering methods can be used to make modified genomes that can be carried into plants and animals by viruses acting as vectors or vehicles. This method can lead to more productive transgenic animals and plants.
Similar modifications (as plants and animals in agriculture) of humans have not been attempted for technical and ethical reasons. But the modification of genes of cells of individuals has been under investigation for many years. This is known as gene therapy.
The key element of gene therapy is the introduction of functioning genes into the cells of a human patient. This new gene shows desired functions and corrects defective or non-operational genes within those cells.
The most common target has been cancers, accounting for almost two-thirds of all clinical trials to date. Adenoviruses are widely used as vectors, and can be engineered both to enhance specificity and to minimize unwanted effects.
Viruses have been used since the time of Edward Jenner in vaccines. Jenner used cow pox viruses to inoculate people against small pox infection.
Vaccines against polio, measles, chicken pox etc. use live and weakened viruses causing the disease or dead virus particles. These, when introduced into an healthy individual, help the immune system to recognise and mount an immunity against the virus. The body remembers the organism and attacks it in case of a later infection thus preventing the disease.
Vaccines for hepatitis B and those for human papillomavirus protect against liver and cervical cancer respectively. Both use selected proteins of the virus (subunit vaccines).
This is a therapy when the target cells are inserted with an enzyme that can activate an inactive a precursor or inactive form of a cytotoxic drug that is administered systemically. Thus, the active, cytotoxic form of the drug is only produced where the relevant enzyme is present and active.
For example, an adenovirus expressing the thymidine kinase (TK) enzyme of herpes simplex virus can be combined with systemic administration of ganciclovir, which is converted by the TK to its active form only in cells where this enzyme is present. This is used in HIV treatment.
Viruses can also be used to control damaging pests. Traditionally this has been used in agriculture, but applications exist in the control of agents important to human health as well.
The types of agents used for this purpose may prey on the target species, may be parasites on the target pests, be pathogens or cause disease in the target species or may be competing species.
Viruses used for pest control are commonly pathogens causing disease of the target species. Although they account for a small amount of total pesticide use, viruses are used for the control of multiple species of insects and also for rabbits.
Biological agents can produce long-lasting effects and in some cases are able to spread among the target population. They have also been recognized as inherently less toxic than conventional pesticides by the US Environmental Protection Agency.
Their disadvantages include limited range of action, slow effects compared to chemical agents, high costs of initial treatment, low environmental stability, particularly in sunlight etc.