introduction
microbfreak@bs
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This blog is set up for our CL1202 module - Microbiology B
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Orthomyxoviridae (1)
Saturday, January 31, 2009/ 11:19 PM
www.flickr.comIntroduction:
For this family of viruses, we'll be focusing on the Influenza virus (type A and B). The influenza virus is a single stranded negative RNA (ss(-) RNA) virus. An influenza virus particle is typically spherical, has an envelope, could be pleomorphic,has spikes on the envelope called haemagglutinin and neuraminidase,the ratio of HA:NA is 5:1.
As mentioned earlier, the virus is a ss(-) RNA in 8 segments. It has 3 polymerase polypeptides with each segment and the 5' and 3' end of the segments are all highly conserved.
Reproductive cycle of the Influenza virus:
There are basically 6 phases for virus replication. They are:
- Attachment
- Penetration
- Uncoating
- Replication
- Assembly
- Release
It takes about 6 hours for the complete replication of the Influenza virus. The reproduction of the virus kills the host cell in process. The virus attaches to the glycolipids or glycoproteins of the cell membrane of the host cell via its haemugglutinin subunit on the virion envelope. Then, the virus is engulfed into the endosomes. The acidic environment of the endosome causes the virus envelope to fuse with the endosome's plasma membrane, and in the process, uncoating the nucleocapsid which is released into the cytoplasm. A transmembrane protein help forms an ion channel for protons to enter the virion and destabilize protein binding. This allows the transport of the nucleocaspid to the nucleus, where the genome is transcribed by important enzymes to get viral mRNA. The nucleocaspid is then assembled in the nucleus. As the virions bud through the host cell membranes, they acquire envelopes and undergo maturation. The viral envelope haemagglutinin may be subjected to degradation(digestion). This process helps the virions to be infectious. Virions that are newly synthesized have surface glycoproteins that contain a N-acetylneuraminic acid as a part of their carbohydrate structure.This factor makes them susceptible to self-agglutination by the hemagglutinin. One of the functions of the viral neuraminidase is to remove these residues, to avoid self-agglutination.
Pathogenesis:
The influenza virus is transmitted from person to person in droplets mostly by sneezing and coughing. The inhaled droplets then land on the lower espiratory tract and the virus starts to invade and infect the mucosal cells. The influenza virus affects the human respiratory tract because of its haemagglutinin's (HA) affinity for receptors in the epithelium of the tract. In an attempt to fight off the virus, the epithelium of the tract produces mucus to trap the virus particles. The virus may extensively infect the alveoli, especially pateints who have lung and heart problems. Some of the compounds that help to fight off these virus are:
- existing antibodies
- Macrophages
- IgA, IgG
- Anti-HA Ab
- Cytokines www.humpath.com
- Natural killer cells
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