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Influenza Viruses Notes
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Lecture notes study book Medical Microbiology of Michael R. Barer, Will L. Irving, Nelun Perera (Chapters 44, 46, and 56) - ISBN: 9780702072000 (Q&S based)
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L12 Influenza VirusesWhat is influenza virus?
A virus causing respiratory diseases. There are three types of influenza virus: Type A, Type B, and Type C
that belong to Orthomyxoviridae family.
Myxo, means that the virus causes disease in the mucus area of the Respiratory Tract
Describe the structure of Influenza virus.
Spherical in shape, with a ss -ive sense RNA genome
Types A & B have 8 segmented genomes, while type C has 7
What are the 9 structural proteins contained within influenza virus particles?
- Nucleoproteins (NP) associated with RNA to form Ribonucleoproteins (RNP)
- PB1, PB2, PA are bound with viral RNP responsible for RNA transcription and replication
- Matrix (M1) Protein which forms a shell below the viral lipid envelop
- Lipid Envelop derived from the cell
- Two Glycoproteins Encoded
Hemagglutinin (HA): used for attachment to surface receptors
Neuraminidase (NA): sialidase enzyme, removing sialic acid from the host cell membrane
- M2 Ion Channel Protein
- Non-Structural Proteins
Why are HA and NA important?
HA and NA are major antigens, required for determining the antigenic variation of influenza virus.
What are the antigenic changes in HA called?
- Minor changes Ü Antigenic Drift
Due to genetic reassortment
- Major changes Ü Antigenic Shift
How are the influenza viruses divided?
Type A Antigenically highly variable
Responsible for most cases of epidemic influenza
in humans
Causes diseases in aquatic birds, horses, and pigs
Type B May exhibit some antigenic changes
Sometimes it may cause epidemic only in
humans
Type C Antigenically stable
Causes infection in swans and humans
What are the Physico-Chemical characteristics of influenza viruses?
, Drying on
glass and Phenol,
Withstand
blankets Storing Lipid Solvents
Ethanol, Light pH
Can be stored UV rays and γ- Virus resists
Ether, And
at 0-4◦C for 2 rays destroy inactivation at
Formaldehyde
weeks the virus alkaline pH
can destroy
Dust for 2 the virus
weeks
Explain the viral attachment, penetration, and uncoating:
Viral envelop and
Virus enters cell within endosome cell
Virus Attaches to
endosomes by membrane fuse
surface Sialic Acid by
Receptor Mediated together and trigger
HA
Endocytosis the uncoating
procedure
Explain the process of viral replication:
mRNA transcription and replication within the nucleus
Host cell protein synthesis is shutdown 3 hours after infection
New progeny viruses produced within 8-10 hours
Negative sense RNA forms Positive strand
RNA replication begins
Nucleocapsids assemble in nucleus
Virus moves out towards the cell surface
HA and NA are synthesized in the ER
HA and NA are inserted into the plasma membrane
Nucleocapsids are inserted into plasma membrane with the help of M1 proteins
Viruses are released by budding from the surface of the cell
NA removes terminal sialic acids from cellular and viral surface glycoproteins
virus particles are released from the cell
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