Reassortment is the mixing of the genetic material of a species into new combinations in different individuals. The product of reassortment is called a reassortant. It is particularly used when two similar viruses that are infecting the same cell exchange genetic material. More specifically, it refers to the swapping of entire segments of the genome, which only occurs between viruses with segmented genomes. [1] (All known viruses with segmented genomes are RNA viruses.)
The classical example of reassortment is seen in the influenza viruses, whose genomes consist of eight distinct segments of RNA. These segments act like mini-chromosomes, and each time a flu virus is assembled, it requires one copy of each segment.
If a single host (a human, a chicken, or other animal) is infected by two different strains of the influenza virus, then it is possible that new assembled viral particles will be created from segments whose origin is mixed, some coming from one strain and some coming from another. The new reassortant strain will share properties of both of its parental lineages.
Reassortment is responsible for some of the major antigenic shifts in the history of the influenza virus. In the 1957 "Asian flu" and 1968 "Hong Kong flu" pandemics, flu strains were caused by reassortment between an avian virus and a human virus. [2] [3] In addition, the H1N1 virus responsible for the 2009 swine flu pandemic has an unusual mix of swine, avian and human influenza genetic sequences. [4]
When influenza viruses are inactivated by UV irradiation or ionizing radiation, they remain capable of multiplicity reactivation in infected host cells. [5] [6] [7] If any of a virus's genome segments is damaged in such a way as to prevent replication or expression of an essential gene, the virus is inviable when it, alone, infects a host cell (single infection). However, when two or more damaged viruses infect the same cell (multiple infection), the infection can often succeed (multiplicity reactivation) due to reassortment of segments, provided that each of the eight genome segments is present in at least one undamaged copy. [8]
The reptarenavirus family, responsible for inclusion body disease in snakes, shows a very high degree of genetic diversity due to reassortment of genetic material from multiple strains in the same infected animal.
Influenza A virus (IAV) is the only species of the genus Alphainfluenzavirus of the virus family Orthomyxoviridae. It is a pathogen with strains that infect birds and some mammals, as well as causing seasonal flu in humans. Mammals in which different strains of IAV circulate with sustained transmission are bats, pigs, horses and dogs; other mammals can occasionally become infected.
Avian influenza, also known as avian flu or bird flu, is a disease caused by the influenza A virus, which primarily affects birds but can sometimes affect mammals including humans. Wild aquatic birds are the primary host of the influenza A virus, which is enzootic in many bird populations.
Antigenic shift is the process by which two or more different strains of a virus, or strains of two or more different viruses, combine to form a new subtype having a mixture of the surface antigens of the two or more original strains. The term is often applied specifically to influenza, as that is the best-known example, but the process is also known to occur with other viruses, such as visna virus in sheep. Antigenic shift is a specific case of reassortment or viral shift that confers a phenotypic change.
Orthomyxoviridae is a family of negative-sense RNA viruses. It includes seven genera: Alphainfluenzavirus, Betainfluenzavirus, Gammainfluenzavirus, Deltainfluenzavirus, Isavirus, Thogotovirus, and Quaranjavirus. The first four genera contain viruses that cause influenza in birds and mammals, including humans. Isaviruses infect salmon; the thogotoviruses are arboviruses, infecting vertebrates and invertebrates. The Quaranjaviruses are also arboviruses, infecting vertebrates (birds) and invertebrates (arthropods).
Antigenic drift is a kind of genetic variation in viruses, arising from the accumulation of mutations in the virus genes that code for virus-surface proteins that host antibodies recognize. This results in a new strain of virus particles that is not effectively inhibited by the antibodies that prevented infection by previous strains. This makes it easier for the changed virus to spread throughout a partially immune population. Antigenic drift occurs in both influenza A and influenza B viruses.
Coinfection is the simultaneous infection of a host by multiple pathogen species. In virology, coinfection includes simultaneous infection of a single cell by two or more virus particles. An example is the coinfection of liver cells with hepatitis B virus and hepatitis D virus, which can arise incrementally by initial infection followed by superinfection.
Influenza A virus subtype H5N1 (A/H5N1) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds. It is enzootic in many bird populations, and also panzootic. A/H5N1 virus can also infect mammals that have been exposed to infected birds; in these cases, symptoms are frequently severe or fatal.
Swine influenza is an infection caused by any of several types of swine influenza viruses. Swine influenza virus (SIV) or swine-origin influenza virus (S-OIV) refers to any strain of the influenza family of viruses that is endemic in pigs. As of 2009, identified SIV strains include influenza C and the subtypes of influenza A known as H1N1, H1N2, H2N1, H3N1, H3N2, and H2N3.
Influenza A virus subtype H1N1 (A/H1N1) is a subtype of influenza A virus (IAV). Some human-adapted strains of H1N1 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs and in birds. Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein.
Influenza A virus subtype H3N2 (A/H3N2) is a subtype of influenza A virus (IAV). Some human-adapted strains of A/H3N2 are endemic in humans and are one cause of seasonal influenza (flu). Other strains of H1N1 are endemic in pigs and in birds. Subtypes of IAV are defined by the combination of the antigenic H and N proteins in the viral envelope; for example, "H1N1" designates an IAV subtype that has a type-1 hemagglutinin (H) protein and a type-1 neuraminidase (N) protein.
Influenza B virus is the only species in the genus Betainfluenzavirus in the virus family Orthomyxoviridae.
The genetic structure of H5N1, a highly pathogenic avian influenza virus, is characterized by a segmented RNA genome consisting of eight gene segments that encode for various viral proteins essential for replication, host adaptation, and immune evasion.
Spanish flu research concerns studies regarding the causes and characteristics of the Spanish flu, a variety of influenza that in 1918 was responsible for the worst influenza pandemic in modern history. Many theories about the origins and progress of the Spanish flu persisted in the literature, but it was not until 2005, when various samples of lung tissue were recovered from American World War I soldiers and from an Inupiat woman buried in permafrost in a mass grave in Brevig Mission, Alaska, that significant genetic research was made possible.
Antigenic variation or antigenic alteration refers to the mechanism by which an infectious agent such as a protozoan, bacterium or virus alters the proteins or carbohydrates on its surface and thus avoids a host immune response, making it one of the mechanisms of antigenic escape. It is related to phase variation. Antigenic variation not only enables the pathogen to avoid the immune response in its current host, but also allows re-infection of previously infected hosts. Immunity to re-infection is based on recognition of the antigens carried by the pathogen, which are "remembered" by the acquired immune response. If the pathogen's dominant antigen can be altered, the pathogen can then evade the host's acquired immune system. Antigenic variation can occur by altering a variety of surface molecules including proteins and carbohydrates. Antigenic variation can result from gene conversion, site-specific DNA inversions, hypermutation, or recombination of sequence cassettes. The result is that even a clonal population of pathogens expresses a heterogeneous phenotype. Many of the proteins known to show antigenic or phase variation are related to virulence.
Influenza, commonly known as the flu, is an infectious disease caused by influenza viruses. Symptoms range from mild to severe and often include fever, runny nose, sore throat, muscle pain, headache, coughing, and fatigue. These symptoms begin one to four days after exposure to the virus and last for about two to eight days. Diarrhea and vomiting can occur, particularly in children. Influenza may progress to pneumonia from the virus or a subsequent bacterial infection. Other complications include acute respiratory distress syndrome, meningitis, encephalitis, and worsening of pre-existing health problems such as asthma and cardiovascular disease.
A recombinant virus may occur naturally or be produced by recombining pieces of DNA or RNA in a laboratory.
The pandemic H1N1/09 virus is a swine origin influenza A virus subtype H1N1 strain that was responsible for the 2009 swine flu pandemic. This strain is often called swine flu by the public media due to the prevailing belief that it originated in pigs. The virus is believed to have originated around September 2008 in central Mexico.
Influenza A virus subtype H7N9 (A/H7N9) is a subtype of the influenza A virus, which causes influenza (flu), predominantly in birds. It is enzootic in many bird populations. The virus can spread rapidly through poultry flocks and among wild birds; it can also infect humans that have been exposed to infected birds.
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.
Orthornavirae is a kingdom of viruses that have genomes made of ribonucleic acid (RNA), including genes which encode an RNA-dependent RNA polymerase (RdRp). The RdRp is used to transcribe the viral RNA genome into messenger RNA (mRNA) and to replicate the genome. Viruses in this kingdom share a number of characteristics which promote rapid evolution, including high rates of genetic mutation, recombination, and reassortment.
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