Influenza virus genome
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Viral entry. Curr Top Microbiol Immunol. Stegmann T. Membrane fusion mechanisms: the influenza hemagglutinin paradigm and its implications for intracellular fusion. Influenza virus M2 protein has ion channel activity. Role of virion M2 protein in influenza virus uncoating: specific reduction in the rate of membrane fusion between virus and liposomes by amantadine. J Gen Virol. A universal influenza A vaccine based on the extracellular domain of the M2 protein.
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Cros JF, Palese P. Trafficking of viral genomic RNA into and out of the nucleus: influenza, Thogoto and Borna disease viruses. Li X, Palese P. Characterization of the polyadenylation signal of influenza virus RNA. The polyadenylation signal of influenza virus RNA involves a stretch of uridines followed by the RNA duplex of the panhandle structure.
Polyadenylation sites for influenza virus mRNA. Krug RM. Evidence for segment-nonspecific packaging of the influenza a virus genome. An influenza virus containing nine different RNA segments. Selective incorporation of influenza virus RNA segments into virions. Structure of the catalytic and antigenic sites in influenza virus neuraminidase.
Structure of the influenza virus glycoprotein antigen neuraminidase at 2. Palese P, Compans RW. Inhibition of influenza virus replication in tissue culture by 2-deoxy-2,3-dehydro-N-trifluoroacetylneuraminic acid FANA : mechanism of action. Characterization of temperature sensitive influenza virus mutants defective in neuraminidase. Neuraminidase is important for the initiation of influenza virus infection in human airway epithelium. Support Center Support Center. External link. This process of comparing genetic sequences is called genetic characterization.
CDC uses genetic characterization for several reasons:. Each sequence from a specific influenza virus has its own branch on the tree. Viruses are grouped by comparing changes in nucleotides within the gene. Viruses which share a common ancestor can also be described as belonging to the same clade. The degree of genetic difference number of nucleotide differences between viruses is represented by the length of the horizontal lines branches in the phylogenetic tree. The further apart viruses are on the horizontal axis of a phylogenetic tree, the more genetically different the viruses are to one another.
Phylogenetic trees of influenza viruses will usually display how similar sequences of the nucleotides for hemagglutinin HA genes of the vaccine virus and circulating viruses are to each other. As part of this process, CDC compares the new virus sequence with the other virus sequences and looks for differences among them. CDC then uses a phylogenetic tree to visually represent how genetically similar the A H3N2 viruses are to each other. In Figure 1, virus b is more genetically similar to virus c than d.
Viruses b and c share a common ancestor and the total length of the horizontal branches is short. CDC performs genetic characterization of influenza viruses year-round. The analysis and selection are made twice each year to recommend vaccine viruses for both the Northern Hemisphere and Southern Hemisphere. In the months leading up to the WHO-facilitated vaccine consultation meetings , where the recommendations are made, CDC collects influenza viruses through surveillance and compares the HA and NA gene sequences of current vaccine viruses against those of circulating flu viruses.
This is one of the ways CDC assesses how closely related the circulating influenza viruses are to the viruses the seasonal flu vaccine was formulated to protect against. Many other data, including antigenic characterization findings and human serology data , shape the vaccine selection decisions. One influenza sample contains many influenza virus particles that were grown in a test tube and that often have small genetic differences in comparison to one another among the whole population of sibling viruses.
Each year in the USA, more than , patients are admitted to hospitals because of influenza and there are approximately 36, influenza-related deaths.
Influenza A virus is found in human and many other animals. There are over subtypes of Influenza A virus. All subtypes have been found in wild birds, which are thought to be a natural reservoir of Influenza A virus and the source of influenza A viruses in all other animals.
For example, pigs may be infected with influenza A viruses from different species e. If these variants spread to humans, then they would not be recognized by the immune system, and so can cause seasonal epidemics of flu. Each year, it is essential to identify new flu virus variants and produce vaccines against them to avoid flu epidemics. National Center for Biotechnology Information , U.
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