Influenza virus; a member of the Orthomyxoviridae familyDescription and Significance
The orthomyxovirus gets its name from the Greek word 'myxa' that means mucus.
Influenza virus types A and B are both common causes of acute respiratory illnesses. Both virus types may cause epidemics of considerable morbidity and mortality but influenza B infections are often limited to localized outbreaks whereas influenza A viruses are the principal cause of larger epidemics including worldwide pandemics. Influenza occurs in winter epidemics that affect 1-5% of the population in temparate regions. Influenza can be contracted throughout the year in tropical regions and its contribution to overall morbidity and mortality is less well defined. (source: World Health Organization: Immunization, Vaccines and Biologicals)
Genome Structure
The genome of the orthomyxovirus consists of six segments to eight segments of linear, negative-sense, single-stranded RNA. The complete genome is 10000-14600 nucleotides long. Segment 1 is fully sequenced and the complete sequence is 2300-2500 nucleotides long. Although sequenced and of the same length as Segment 1, segment 2 only has an estimate of the sequence so far. Segment 3 is also sequenced, but only estimated, and the complete sequence is 2200-2300 nucleotides long. Segment 4 has been completely sequenced and the complete sequence is 1700-1800 nucleotides long. Segment 5 has been sequenced, but only estimated, and is 300-1900 nucleotides long. Segment 6 has been sequenced, but only estimated, and is 1400-1500 nucleotides long. Segment 7 has been sequenced, but only estimated, and the complete sequence is 800-1100 nucleotides long. The genome has terminally redundant sequences and the sequence is repeated at both ends. The nucleotide sequences at the 3'-terminus are identical. The 5'-terminal sequence has conserved regions and repeats complementary to the 3'-terminus; terminal repeats at the 5'-end are 11-14 nucleotides long. The 3'-terminus has conserved nucleotide sequences; is 11-13 nucleotides long; in the genera of same family. The sequence has conserved regions in all RNA species or some RNA segments. The multipartite genome is encapsidated with each segment in a separate nucleocapsid, and the nucleocapsids are surrounded by one envelope. Each virion contains defective interfering copies.
Virion Structure of an Orthomyxovirus
The virions of an orthomyxovirus consist of an envelope, a matrix protein, a nucleoprotein complex, a nucleocapsid, and a polymerase complex. The virus capsid is enveloped. The virions are spherical to pleomorphic and filamentous forms occur. The virions are 80-120 nm in diameter and 200-300(-3000) nm long. The surface projections are densely dispersed distinctive hemagglitinin-esterase (HEF) spikes, or spaced widely apart hemagglutinin (HA) spikes. Clusters of neuramidase (NA) irregularly inerpose the major glycoprotein in a ratio of HA to NA about 4-5 to 1. There are about 500 spikes evenly dispersed or clustered and are covering the surface comprising hemagglutinin, or neuraminidase, or esterase-esterase. The surface projections are composed of one type of protein or different types of proteins and are 10-14 nm long and 4-6 nm in diameter. The nucleocapsid is elongated with helical symmetry and is segmented with loops at one end. The segments have different sized classes with clear predominate lengths with a length of 50-130 nm (in differnent class sizes) and a width of 9-15 nm.
The virions of an orthomyxovirus consist of an envelope, a matrix protein, a nucleoprotein complex, a nucleocapsid, and a polymerase complex. The virus capsid is enveloped. The virions are spherical to pleomorphic and filamentous forms occur. The virions are 80-120 nm in diameter and 200-300(-3000) nm long. The surface projections are densely dispersed distinctive hemagglitinin-esterase (HEF) spikes, or spaced widely apart hemagglutinin (HA) spikes. Clusters of neuramidase (NA) irregularly inerpose the major glycoprotein in a ratio of HA to NA about 4-5 to 1. There are about 500 spikes evenly dispersed or clustered and are covering the surface comprising hemagglutinin, or neuraminidase, or esterase-esterase. The surface projections are composed of one type of protein or different types of proteins and are 10-14 nm long and 4-6 nm in diameter. The nucleocapsid is elongated with helical symmetry and is segmented with loops at one end. The segments have different sized classes with clear predominate lengths with a length of 50-130 nm (in differnent class sizes) and a width of 9-15 nm.
ref:http://microbewiki.kenyon.edu/index.php/Orthomyxoviridae
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