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Family: Paramixovirus

Paramyxovirus (from Greek para, beyond, myxo, mucus or slime, virus, from Latin poison, slime) are single-stranded RNA (ssRNA) viruses belonging to the family Paramyxoviridae. These viruses, including measles, mumps, human respiratory syncytial virus, Newcastle disease virus, Sendai virus, etc., are causative agents of many diseases in animals and humans.

Table of Contents

1. Morphology 2. Physical and Physiochemical Properties 3. Chemistry a. Nucleic Acids b. Proteins c. Lipids d. Carbohydrates 4. Life Cycle 5. Hosts 6. Taxonomy 7. Important Members 8. Pathology a. Antigenicity b. Parthogenic Paramyxoviruses 9. External Links

Morphology [top]

The members of viruses in family Paramyxoviridae are classified as enveloped viruses which are composed of a nucleocapsid, and a matrix protein. These viruses are similar in morphology to the influenza viruses. The virus capsid is enveloped and mature naturally by budding through the membrane of the host cell. The virus shapes can be spherical to pleomorphic; filamentous and other forms. The size of these viruses are 150-200 nm in diameter and 1000-10000 nm in length.

3D image of of Pneumovirus reconstruction originates from the University of Warwick, Pneumovirus Laboratory, UK

The envelope surface is evenly covered with hemagglutinin-neuraminidase (HN) and fusion proteins (F) which are embedded in a lipid bilayer. The lipid bilayer is comprised of hemagglutinin-neuraminidase (HN), or hemagglutinin (H), or surface glycoproteins (GP), or fusion proteins. The surface of viruses have spike-liked projections, 8-12 nm in length and 6-10 nm apart (depends on the genus). The capsid/nucleocapsid is elongated and exhibits helical symmetry. The nucleocapsid is filamentous, flexuous, and varies in length with the usual being 600-800 nm (depends on the genus), and width of 13-18 nm. The basic helix is obvious. Pitch of helix is 5.5-7 nm (depending on the subfamily). The nucleocapsid is not segmented.
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Physical and Physiochemical Properties [top]

Molecular mass	500 MDa
Buoyant density in CsCl	1.18 - 1.31 g cm-3
Buoyant density in sucrose	1.18 - 1.2 g cm-3
Sedimentation coefficient	at least 1000 S20w
Sensitive to these treatments	- Non-ionic detergents - Lipid solvents - Formaldehyde - Oxidizing agents - heat

Chemistry [top]

Nucleic Acids Nucleic acids are 0.5 % of the virus by weight. The genome is monomeric or multiploid negative-sense, single-stranded RNA, non-segmented. The genome is not infectious. The length varies from 15200 to 15900 nucleotides long, encoding 7-11 proteins. Single copy of the genome without 5'-end cap and the covalent attachment to terminal protein. There is no poly (A) tail at 3'-terminus. The gene sequence is across the family is:    Nucleocapsid - Phosphoprotein - Matrix - Fusion - Attachment - Large (polymerase) [Source]

Proteins Protein Name Function Notes N nucleocapsid protein associates with genomic RNA (one molecule per hexamer) and protects the RNA from nuclease digestion P phosphoprotein binds to the N and L proteins and forms part of the RNA polymerase complex M matrix protein assembles between the envelope and the nucleocapsid core; organizes and maintains virion structure F fusion protein projects from the envelope surface as a trimer, and mediates cell entry by inducing fusion between the viral envelope and the cell membrane by class I fusion One of the defining characteristics of members of the paramyxoviridae family is the requirement for a neutral pH for fusogenic activity. H/HN/G attachment proteins span the viral envelope and project from the surface as spikes; bind to sialic acid on the cell surface and facilitate cell entry The receptor for measles virus is unknown. Proteins are designated H for morbilliviruses and henipaviruses as they possess haemagglutination activity, observed as an ability to cause red blood cells to clump. HN attachment proteins occur in respiroviruses and rubulaviruses. These possess both haemagglutination and neuraminidase activity which cleaves sialic acid on the cell surface, preventing viral particles from reattaching to previously infected cells. Attachment proteins with neither haemagglutination nor neuraminidase activity are designated G (glycoprotein). These occur in members of pneumovirinae. L large protein the catalytic subunit of RNA dependent RNA polymerase (RDRP) n/a accessory proteins a mechanism known as RNA editing (see Mononegavirales) allows multiple proteins to be produced from the P gene. These are not essential for replication but may aid in survival in vitro or may be involved in regulating the switch from mRNA synthesis to antigenome synthesis. [Source] Protein locations [Image Source]

Lipids Lipids are 20-25 % of the virus by weight. They are found in lipid bilayer, the structure of the viral envelope. The composition of viral lipids is similar to that of the host cell membranes. The lipids are of host origin and are derived from plasma membranes. [Source]

Carbohydrates Carbohydrates constitute 6% of virus by dry weight. They are host-dependent. They are present as glycoproteins: - N-linked glycan (side chains found in the fusion and attachment proteins) - O-linked glycosidic side chain (in the attachment protein G in the subfamily Pneumoviridae) - Polylactosamine (in the SH protein of Respiratory syncytical virus) [Source]

Life Cycle - Replication [top]

Paramyxovirus replication is very similar to that of other viruses in this group. The overall strategy of paramyxoviruses is very similar to that of influenza. However, all action in the replication of paramyxoviruses occurs in the cytoplasm.

The viruses attach to the surface of a host cell, and the envelope fuses to the plasma membrane. The nucleocapsid is released into the cell and used as the genomic template. The negative-sense RNA is transcribed into individual messenger RNAs and a positive-sense RNA template, which is used to create further the negative-sense RNA. Assembly occurs, and new viruses bud from the cell membrane and get the envelopes. For the paramyxoviruses, they have the ability to cause cell-to-cell fusion, creating large multinucleated cells called syncytia.

Replication cycle Accumulations of virions in vitro are sensitive to amantadine, an anti-viral drug.

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Replication cycle of measles virus, a virus in the Paramyxoviridae family
[Image Source: Source: (Moss WJ, Griffin DE. Global measles elimination. Nat Rev Microbiol. 2006 Dec;4(12):900-8. Epub 2006 Nov 6.)]

Hosts [top]

Viruses can infect various invertebrate hosts including human, dogs, seals, dolphins and porpoises, birds and cattle.
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Taxonomy [top]

• Order Mononegavirales (Wikipedia, NCBI taxonomy, ICTVdb)
  
  • Family Paramyxoviridae (Wikipedia, NCBI taxonomy, ICTVdb, ICTVdb picture gallery)
    
    • Subfamily Paramyxovirinae (NCBI taxonomy, ICTVdb)
      
      • Genus Avulavirus (Wikipedia, NCBI taxonomy, ICTVdb)
        
        • Newcastle disease virus (Wikipedia, NCBI taxonomy)
          
      • Genus Henipavirus (Wikipedia)
        
        • Hendra virus (NCBI taxonomy)
          
        • Nipah virus (NCBI taxonomy)
      • Genus Morbillivirus (Wikipedia, NCBI taxonomy, ICTVdb)
        
        • Measles virus (Wikipedia, NCBI Taxonomy,ICTVdb)
      • Genus Respirovirus (NCBI taxonomy, ICTVdb)
        
        • Sendai virus (Wikipedia, NCBI taxonomy, ICTVdb)
      • Genus Rubulavirus (Wikipedia, NCBI taxonomy, ICTVdb)
        
        • Mumps virus (Wikipedia, NCBI taxonomy, ICTVdb)
    • Subfamily Pneumovirinae (NCBI taxonomy, ICTVdb)
      
      • Genus Metapneumovirus (Wikipedia, NCBI taxonomy, ICTVdb)
        • Human metapneumovirus (NCBI taxonomy)
      • Genus Pneumovirus (NCBI taxonomy, ICTVdb)
        • Human respiratory syncytial virus (Wikipedia, NCBI taxonomy, ICTVdb)
    • Unclassified Paramyxoviridae

The full list of paramyxovirus (family Paramyxoviridae): NCBI taxonomy browser, Viral Bioinfornatics Resource Center.
Pictures of paramyxovirus: The big picture book of viruses.

Important Members [top]

Measles virus

Human Metapneumovirus

Mumps Virus

Pathology [top]

Antigenicity The antigenicity of the virus corresponds to: Major structural glycoproteins at the envelope's surface; Viral attachment proteins (HN, or H, or G); Fusion protein (F)

Pathogenic paramyxoviruses A number of important human diseases are caused by paramyxoviruses. These include mumps, measles, which caused 745,000 deaths in 2001 and respiratory syncytial virus (RSV) which is the major cause of bronchiolitis and pneumonia in infants and children. The parainfluenza viruses are the second most common causes of respiratory tract disease in infants and children. They can cause pneumonia, bronchitis and croup in children and the elderly. Human metapneumovirus (HMVP), initially described in about 2001, is also implicated in bronchitis, especially in children. Paramyxoviruses are also responsible for a range of diseases in other animal species, for example canine distemper virus (dogs), phocine distemper virus (seals), cetacean morbillivirus (dolphins and porpoises) Newcastle disease virus (birds) and rinderpest virus (cattle). Some paramyxoviruses such as the henipaviruses are zoonotic pathogens, occurring naturally in an animal host, but also able to infect humans. Hendra virus (HeV) and Nipah virus (NiV) in the genus Henipavirus have emerged in humans and livestock in Australia and Southeast Asia. Both viruses are contagious, highly virulent, and capable of infecting a number of mammalian species and causing potentially fatal disease. Due to the lack of a licensed vaccine or antiviral therapies, HeV and NiV are designated as biosafety level (BSL) 4 agents. The genomic structure of both viruses is that of a typical paramyxovirus. The virus is probably distributed worldwide. [Source]

External Links [top]

Wikipedia
GenBank
ICTVdb
Viral Zone