Antigenic Shift
Antigenic shift is a process in which the genetic material of a virus, particularly influenza viruses, undergoes a major change, resulting in the emergence of a new strain. This can occur when two different strains of the virus infect the same host and exchange genetic material, leading to a novel virus with the potential to cause widespread illness.
3 Key excerpts on "Antigenic Shift"
eBook - ePub- Irina Kiseleva, Natalie Larionova(Authors)
- 2021(Publication Date)
- Bentham Science Publishers(Publisher)
...Circulating influenza B viruses belong to two major genetically distinct lineages (B/Victoria and B/Yamagata) (for more details, see Chapter 3). Influenza viruses evolve through the gradual accumulation of mutations, which is a molecular basis of antigenic drift and genome reassortment (a phenomenon called Antigenic Shift). New drifted antigenic variants of H3N2 viruses appear every 2–5 years. In contrast, new antigenic variants of H1N1 or influenza B viruses appear less frequently (3–8 years) [ 18 - 20 ]. Reassortment is also of evolutionary importance. Although most new genomic constellations will be unviable or deleterious, some of them may facilitate adaptation to new hosts, help evade host immune responses, and assist in the development of drug-resistance [ 11 ]. Reassortants of human, swine, or avian influenza viruses were detected [ 21, 22 ]. For instance, in 2010-2011, influenza H3N2 variant viruses (H3N2v) with the matrix (M) gene from the 2009 H1N1 pandemic virus were first identified in pigs and humans. Genetically distinct lineages of influenza virus B can co-circulate in the population and reassort [ 23, 24 ]. One of the most famous reassortants is the triple-reassortant that caused the 2009 pandemic [ 25 ]. Escaping from the Immune Response Infection with an influenza virus induces innate and adaptive immune responses. The high variability of HA allows influenza viruses to escape from host immune surveillance and results in seasonal outbreaks. Viruses use various strategies to evade immune responses, resulting in the reduced clearing of the virus and virus-infected cells [ 26 ]. The evasion of influenza viruses from innate and adaptive immune responses reduces the effectiveness of vaccination. Escape immunity allows the virus to reinfect individuals who were once immune to the virus and necessitating reformulation of the seasonal influenza virus vaccine [ 27 ]. Vaccine formulations need to be updated every year to provide adequate protection...
eBook - ePubFrom Killer To Common Cold
Herd Protection and the Transitional Phase of Covid-19
- David M Graham(Author)
- 2020(Publication Date)
- FiPhysician(Publisher)
...At the very minimum, there should be some cross reactivity or partial immunity to any drifted strain. Instead of drifting to evade the immune system, the problem with coronavirus is that immunity to it is not long lasting. In 6-24 months, despite having a perfectly adequate initial immune response, you might get the same virus again as your immunity wanes. Thus, drift is not the issue with relapsing Covid-19 infections, but rather, loss of immunity. Immunity to influenza, on the other hand, can be extremely long lasting. In fact, when H1N1 returned in 2009, those who had it when it last circulated in the 1960’s were usually still immune. Thus, the elderly, despite their weakened immune systems due to normal aging, were relatively protected from H1N1. Unlike coronavirus, influenza may evoke long-lasting immunity after infection. While antigenic drift causes seasonal influenza as the virus slowly mutates over time, Antigenic Shift causes pandemics of influenza. Antigenic Shift is a major genetic change that usually involves the reassortment of influenza from another animal species. There are non-human animals that carry influenza—most commonly pigs and birds. What if human and bird influenza strains co-infect a pig simultaneously and the virus recombines? The pig might start producing humanized bird strains of influenza. These recombinant strains pass back to a human, and if effective human-to-human transmission occurs, a new influenza pandemic begins. Antigenic Shift is reflected by the H and N monikers of influenza. For example, H1 and H3 correspond to human pathogens currently, while H5 and H7 correspond to bird pathogens. The N can be different as well, as in N1, or N9. H and N are important functional proteins influenza carries that allow us to specifically identify them. If influenza swaps out its human H1 for a bird one, then a virus for which there is no baseline immunity may be born...
eBook - ePub- Ethne Barnes(Author)
- 2007(Publication Date)
- University of New Mexico Press(Publisher)
...Only a few of the subtypes infect humans. Each subtype produces antigenic variants within its lineage (genetic drift) affecting one or both protein spikes without altering its subtype identity. Therefore, more than one variant of subtype H1N1 can be circulating within host populations at the same time or at different times. Subtypes of A influenza virus tend to progressively change antigenic appearances in response to animal or human host immune responses in order to survive within their host populations. When a subtype changes host species, the virus often makes adjustments to the new host by modifying its inner core to adapt to and reproduce more efficiently in the new host’s target cells (Scholtissek 1992). Otherwise the change in host species might not allow the virus to reproduce sufficiently for it to be transmitted within the new host population. Occasionally a hybrid virus (genetic shift) arises from two different subtypes and exhibits a new combination of protein spikes, such as an H2N2 subtype versus H1N1. The new hybrid subtype may produce only mild infection at first. More serious disease occurs with progressive changes in antigenic identity as the hybrid virus continues to adjust to its host, or when it changes host species. Or the reverse can take place, with the new hybrid virus first producing severe disease before adjusting to its host and tempering its effects to produce mild disease. Pigs have been known to act as the primary “mixers” for creating hybrid subtypes. They easily get infected by both human and bird subtypes of the same viruses, and when infected by both at the same time, the different subtypes can swap genetic segments to produce a hybrid virus (Scholtissek et al. 1998; Webster 1993). The new hybrid can then be transmitted from pigs to people, where it can modify its inner core and become capable of transmission between humans...
