A gradual change in the antigenicity of a virus arising from the accumulation of mutations in the genes that code for surface proteins, which may result in new strains of the virus that are not as effectively inhibited by the same hostantibodies that prevented infection by the original strain. Antigenic drift is often enabled by the natural selection of mutant strains under pressure from an immune response. Contrast antigenic shift.
Any sudden and major change in the antigenicity of a virus, particularly as the result of a reassortment event between two or more different strains of a virus, or two or more different viruses, which exchange genetic material and thereby combine to form a new subtype having a mixture of the surface antigens of the original strains. Contrast antigenic drift.
A class of antimicrobial medication used specifically for treating diseases caused by viral infections rather than ones caused by bacteria or other infectious agents. Unlike most antibiotics, antivirals typically do not destroy their target viruses but instead inhibit their development. They are distinct from virucides.
The construction of the virus within the host cell, powered by the host's metabolism.
The first stage of infection of a host cell by a virus, in which a chance collision occurs between a viral particle and a suitable receptor area on the cell's surface, allowing the viral particle to physically attach to the cell by electrostatic forces. Absence of suitable attachment areas can give a cell immunity from infection.
A mutant viral strain which has low virulence or is avirulent in one or more of its natural host species, and in which it can thus be used as an attenuated vaccine. Attenuated strains are obtained by passage in cell culture or by sampling from a different host species than the one in which the virus usually causes disease.
Any change in the structure, morphology, or physiology of a host cell that is caused by viral invasion. Common examples of CPEs include rounding of the infected cell, fusion with adjacent cells to form syncytia, and the appearance of nuclear or cytoplasmic inclusion bodies. These changes may or may not cause lysis and cell death.
A double-stranded DNA virus; i.e. a virus whose genome is encoded in two complementary strands of DNA, which usually exist as one or more circular molecules. dsDNA viruses constitute Group I in the Baltimore classification system and use methods of replication and transcription that are broadly similar to those of larger organisms such as bacteria.
A very large virus, especially one of the so-called nucleocytoplasmic large DNA viruses (NCLDVs), which have extremely large genomes compared to the average virus and contain many unique genes not found in other organisms. Some of these viruses are larger than a typical bacterium.
Any larger organism which harbors a virus in some kind of symbiotic relationship, whether parasitic or otherwise. Though some viruses can survive for short periods outside of a host, all viruses are obligate parasites and therefore ultimately depend upon a host in order to reproduce. Their reproduction is by definition harmful to the host in which it occurs, though viruses may also passively infect and be transmitted by intermediate hosts to whom they do little or no harm.
The specificity with which certain pathogens, including most viruses, infect particular hosts and host tissues. Host tropism results in most pathogens being capable of infecting only a limited range of host organisms.
1. The ability of a pathogenic virus to lie dormant or latent within a cell for a period of time before reactivating and producing new, independent virions.
2. The phase in the life cycle of certain viruses in which, after initial infection, proliferation of virus particles ceases while the viral genome remains silently assimilated into the host cell's genome, sometimes indefinitely. The latent period ends when the virus reactivates and begins producing large amounts of viral progeny without the host cell being infected by additional external virions. Latency is a defining element of the lysogenic form of viral replication.
Also called antigenic imprinting and the Hoskins effect.
The tendency of the human body's immune system to preferentially utilize immunological memory of a previous infection when a second, slightly different version of the pathogen (e.g. a virus or bacterium) is encountered in subsequent infections. The success of antibodies developed against the dominant antigens of the original infection establishes an "imprint" on the immune system which governs antibody responses to later infections, even if later infections are caused by variants with different dominant antigens. The result is that the immune system is unable to mount potentially more effective responses to the later infections, and any disease caused by the infection is more serious than before.
A non-genetic interaction in which viral particles produced by a cell that is coinfected with two or more viruses are constructed with a common set of coat proteins shared between all of the infecting agents, but nevertheless retain their own unique viral genomes. This admixture results in viruses which possess similar assortments of identifying surface proteins despite having different genetic material, and as such is exclusively phenotypic, in the sense that if one of these viruses were to proceed to infect another cell alone (i.e. without coinfection), its genetic material would not be capable of reproducing the same set of shared proteins in its own progeny.
A bacteriophage genome that has been inserted and integrated into a circular bacterial chromosome or which exists as an extrachromosomal plasmid inside the host bacterium, specifically while it remains in a latent form that is present inside the host cell but has not yet been activated by it.
The mixing of genetic material from different species or strains into new combinations in different individuals. Reassortment may occur when two or more similar viruses (e.g. two different strains of influenza virus) infect a single host cell, permitting the assembly of new viral particles from segments of each parental lineage.
A subviral agent that depends entirely upon a coinfectinghelper virus for its own replication. Satellites may occur as independent virions which encode structural proteins but nevertheless cannot replicate without the helper virus, or as simple segments of nucleic acids which have "hitchhiked" using proteins encoded by the helper virus.
A laboratory technique by which bacteria or viruses are cultured in serial iterations (e.g. viral particles of a virus grown in one environment are transferred into a new environment, often with slightly different conditions) in order to induce the virus to adapt to novel environments over a period of time. The technique is often used to study viral evolution and to genetically engineer viruses with reduced virulence which can be used in vaccines.
Any virus or virus-like agent that is etiologically associated with a so-called slow virus disease: a disease which, after an extended period of latency, follows a slow, progressive course ranging from months to years before in most cases inevitably progressing to death.
The process by which a cell that has previously been infected by a virus becomes co-infected by a different strain or species of virus as a consequence of the treatment being used to manage the first virus. The second virus has often evolved a resistance to antiviral drugs used to treat the original infection, or an ability to overcome the host's immune response.
A numerical expression of the quantity of virus in a given volume, typically expressed as the number of individual viral particles per unit volume but also by quantifying other factors that are closely related to or influenced by viral concentration. Viral load often correlates with the severity of an active viral infection.
A singular, stable particle that is the independent form in which a virus exists while not inside an infected cell or in the process of infecting a cell. Virions are the products of a completed viral replication cycle; upon release from the infected cell, they are fully capable of infecting other cells of the same type.
The study of viruses and virus-like agents, which seeks to understand and explain their structure, classification, evolution, and mechanisms of infection, as well as the diseases they cause, techniques to isolate and culture them, and their use in research and therapy. Virology is often considered a subfield of microbiology or of medical science.
The active uptake by a host cell of viral particles (typically bound to receptors on the cell surface) by a non-specific pinocytic process. Viropexis is an important method of viral penetration of host cells.
The capacity of a pathogen to cause disease, defined broadly in terms of the severity of symptoms experienced by an infected host. Other factors being equal, a viral strain which causes severe symptoms in a susceptible individual may be considered highly virulent, while a different strain which produces less severe or no symptoms in the same individual may be considered relatively less virulent. In practice the concept of virulence can be of ambiguous interpretation, because a particular strain is not itself solely responsible for the severity of the disease which actually develops; equally important are the degree of infectivity expressed by the strain and the state of the host's immunity, either natural or acquired, with respect to that particular strain.
A submicroscopic infectious agent that replicates only inside the living cells of other organisms. As obligate intracellular parasites, viruses must infect cellular hosts in order to complete their life cycles, which they achieve by co-opting or "hijacking" the host cell's molecular machinery for their own reproduction. While not inside an infected cell or in the process of infecting a cell, viruses exist in the form of independent virions. Most virions are exceedingly simple in structure and physically minute, averaging just 1⁄100 the size of the typical bacterium. Viruses are found in almost every ecosystem on Earth and infect all types of life forms, from animals and plants to microorganisms such as bacteria and archaea.
virus attachment protein
Any protein which helps to facilitate the binding of a virus to a receptor on a host cell.