A plaque-forming unit (PFU) is a measure used in virology to describe the number of virus particles capable of forming plaques per unit volume. [1] It is a proxy measurement rather than a measurement of the absolute quantity of particles: viral particles that are defective or which fail to infect their target cell will not produce a plaque and thus will not be counted.
For example, a solution of tick-borne encephalitis virus with a concentration of 1,000 PFU/μL indicates that 1 μL of the solution contains enough virus particles to produce 1000 infectious plaques in a layer of cells. However, the number of virus particles might be greater than the number of PFU if some virus particles fail to form plaques because they are defective or otherwise failed to infect cells. The concept of plaque-forming units of virus is equivalent to the concept of colony-forming units of bacteria.
Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, their interaction with host organism physiology and immunity, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy.
Viral load, also known as viral burden, is a numerical expression of the quantity of virus in a given volume of fluid, including biological and environmental specimens. It is not to be confused with viral titre or viral titer, which depends on the assay. When an assay for measuring the infective virus particle is done, viral titre often refers to the concentration of infectious viral particles, which is different from the total viral particles. Viral load is measured using body fluids sputum and blood plasma. As an example of environmental specimens, the viral load of norovirus can be determined from run-off water on garden produce. Norovirus has not only prolonged viral shedding and has the ability to survive in the environment but a minuscule infectious dose is required to produce infection in humans: less than 100 viral particles.
Viral evolution is a subfield of evolutionary biology and virology that is specifically concerned with the evolution of viruses. Viruses have short generation times, and many—in particular RNA viruses—have relatively high mutation rates. Although most viral mutations confer no benefit and often even prove deleterious to viruses, the rapid rate of viral mutation combined with natural selection allows viruses to quickly adapt to changes in their host environment. In addition, because viruses typically produce many copies in an infected host, mutated genes can be passed on to many offspring quickly. Although the chance of mutations and evolution can change depending on the type of virus, viruses overall have high chances for mutations.
Defective interfering particles (DIPs), also known as defective interfering viruses, are spontaneously generated virus mutants in which a critical portion of the particle's genome has been lost due to defective replication or non-homologous recombination. The mechanism of their formation is presumed to be as a result of template-switching during replication of the viral genome, although non-replicative mechanisms involving direct ligation of genomic RNA fragments have also been proposed. DIPs are derived from and associated with their parent virus, and particles are classed as DIPs if they are rendered non-infectious due to at least one essential gene of the virus being lost or severely damaged as a result of the defection. A DIP can usually still penetrate host cells, but requires another fully functional virus particle to co-infect a cell with it, in order to provide the lost factors.
Picornaviruses are a group of related nonenveloped RNA viruses which infect vertebrates including fish, mammals, and birds. They are viruses that represent a large family of small, positive-sense, single-stranded RNA viruses with a 30 nm icosahedral capsid. The viruses in this family can cause a range of diseases including the common cold, poliomyelitis, meningitis, hepatitis, and paralysis.
Plant viruses are viruses that have the potential to affect plants. Like all other viruses, plant viruses are obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses can be pathogenic to vascular plants.
In microbiology, the multiplicity of infection or MOI is the ratio of agents to infection targets. For example, when referring to a group of cells inoculated with virus particles, the MOI is the ratio of the number of virus particles to the number of target cells present in a defined space.
A viroplasm, sometimes called "virus factory" or "virus inclusion", is an inclusion body in a cell where viral replication and assembly occurs. They may be thought of as viral factories in the cell. There are many viroplasms in one infected cell, where they appear dense to electron microscopy. Very little is understood about the mechanism of viroplasm formation.
Herpes simplex virus1 and 2, also known by their taxonomic names Human alphaherpesvirus 1 and Human alphaherpesvirus 2, are two members of the human Herpesviridae family, a set of viruses that produce viral infections in the majority of humans. Both HSV-1 and HSV-2 are very common and contagious. They can be spread when an infected person begins shedding the virus.
Phycodnaviridae is a family of large (100–560 kb) double-stranded DNA viruses that infect marine or freshwater eukaryotic algae. Viruses within this family have a similar morphology, with an icosahedral capsid. As of 2014, there were 33 species in this family, divided among 6 genera. This family belongs to a super-group of large viruses known as nucleocytoplasmic large DNA viruses. Evidence was published in 2014 suggesting that specific strains of Phycodnaviridae might infect humans rather than just algal species, as was previously believed. Most genera under this family enter the host cell by cell receptor endocytosis and replicate in the nucleus. Phycodnaviridae play important ecological roles by regulating the growth and productivity of their algal hosts. Algal species such Heterosigma akashiwo and the genus Chrysochromulina can form dense blooms which can be damaging to fisheries, resulting in losses in the aquaculture industry. Heterosigma akashiwo virus (HaV) has been suggested for use as a microbial agent to prevent the recurrence of toxic red tides produced by this algal species. Phycodnaviridae cause death and lysis of freshwater and marine algal species, liberating organic carbon, nitrogen and phosphorus into the water, providing nutrients for the microbial loop.
A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are found in almost every ecosystem on Earth and are the most numerous type of biological entity. Since Dmitri Ivanovsky's 1892 article describing a non-bacterial pathogen infecting tobacco plants and the discovery of the tobacco mosaic virus by Martinus Beijerinck in 1898, more than 11,000 of the millions of virus species have been described in detail. The study of viruses is known as virology, a subspeciality of microbiology.
A neutralizing antibody (NAb) is an antibody that defends a cell from a pathogen or infectious particle by neutralizing any effect it has biologically. Neutralization renders the particle no longer infectious or pathogenic. Neutralizing antibodies are part of the humoral response of the adaptive immune system against viruses, bacteria and microbial toxin. By binding specifically to surface structures (antigen) on an infectious particle, neutralizing antibodies prevent the particle from interacting with its host cells it might infect and destroy.
Virus quantification is counting or calculating the number of virus particles (virions) in a sample to determine the virus concentration. It is used in both research and development (R&D) in academic and commercial laboratories as well as in production situations where the quantity of virus at various steps is an important variable that must be monitored. For example, the production of virus-based vaccines, recombinant proteins using viral vectors, and viral antigens all require virus quantification to continually monitor and/or modify the process in order to optimize product quality and production yields and to respond to ever changing demands and applications. Other examples of specific instances where viruses need to be quantified include clone screening, multiplicity of infection (MOI) optimization, and adaptation of methods to cell culture.
The plaque reduction neutralization test is used to quantify the titer of neutralizing antibody for a virus.
Gene therapy utilizes the delivery of DNA into cells, which can be accomplished by several methods, summarized below. The two major classes of methods are those that use recombinant viruses and those that use naked DNA or DNA complexes.
Chlorovirus, also known as Chlorella virus, is a genus of giant double-stranded DNA viruses, in the family Phycodnaviridae. This genus is found globally in freshwater environments where freshwater microscopic algae serve as natural hosts. There are 19 species in this genus.
This glossary of virology is a list of definitions of terms and concepts used in virology, the study of viruses, particularly in the description of viruses and their actions. Related fields include microbiology, molecular biology, and genetics.
Mammalian orthoreovirus (MRV) is a double-stranded RNA virus. It is a part of the family Reoviridae, as well as the subfamily Spinareovirinae. As seen in the name, the Mammalian Ortheoreovirus infects numerous mammalian species and vertebrates which serve as natural hosts. Some diseases that occur as a result of this virus or are associated with this virus include mild upper respiratory illness, and gastrointestinal illness. Examples of these are: upper respiratory tract syndromes, gastroenteritis, biliary atresia, obstructive hydrocephalus, jaundice, alopecia, conjunctivitis, and ‘oily hair’ associated with steatorrhea.
A therapeutic interfering particle is an antiviral preparation that reduces the replication rate and pathogenesis of a particular viral infectious disease. A therapeutic interfering particle is typically a biological agent (i.e., nucleic acid) engineered from portions of the viral genome being targeted. Similar to Defective Interfering Particles (DIPs), the agent competes with the pathogen within an infected cell for critical viral replication resources, reducing the viral replication rate and resulting in reduced pathogenesis. But, in contrast to DIPs, TIPs are engineered to have an in vivo basic reproductive ratio (R0) that is greater than 1 (R0>1). The term "TIP" was first introduced in 2011 based on models of its mechanism-of-action from 2003. Given their unique R0>1 mechanism of action, TIPs exhibit high barriers to the evolution of antiviral resistance and are predicted to be resistance proof. Intervention with therapeutic interfering particles can be prophylactic (to prevent or ameliorate the effects of a future infection), or a single-administration therapeutic (to fight a disease that has already occurred, such as HIV or COVID-19). Synthetic DIPs that rely on stimulating innate antiviral immune responses (i.e., interferon) were proposed for influenza in 2008 and shown to protect mice to differing extents but are technically distinct from TIPs due to their alternate molecular mechanism of action which has not been predicted to have a similarly high barrier to resistance. Subsequent work tested the pre-clinical efficacy of TIPs against HIV, a synthetic DIP for SARS-CoV-2 (in vitro), and a TIP for SARS-CoV-2 (in vivo).
Virivore comes from the English prefix viro- meaning virus, derived from the Latin word for poison, and the suffix -vore from the Latin word vorare, meaning to eat, or to devour; therefore, a virivore is an organism that consumes viruses. Virivory is a well-described process in which organisms, primarily heterotrophic protists, but also some metazoans consume viruses.
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