PMB: Influenza 14 Flashcards
What microorganism causes influenza?
A negative stranded - single stranded RNA virus. The virus is part of the Orthomyxoviridae
There are 3 species of human influenza: A,B and C. Influenza D affects cattle and not humans.
What is the nomenclature used to describe influenza?
- Antigenic type
- Host species of origin (no host speices for human origin)
- Geographical orign
- Strain number
- Year of isolation
- Haemagglutin
How is influenza transmitted?
Transmission is airbone from person to person via aeorsols
Describe the stucture of influenza
- Particles are spherical
- Approx 100nm diameter
- Structures on the surface help with infection process
- Different proteins types present are used to help with classification
Describe the classification of bacteria
- Protein types present of Neuroaminidase and Haemagglutinin present are used to help classifiy and name the virus e.g. H1N1, H5N1
Describe Haemagglutinin
Cylindrical glycoproteins on the membrane surface
- Binds virus to target cell. Binds virus to the membrane cellular oligosaccharides with sialic acid attached
- In vitro causes the clumping (aglutination) of erythrocytes (RBC) - hence name
Describe Neuraminidases
- Part of the glycosidic hydrolyase family
- Cleaves glycosidic bonds in Neuraminic acid
- Essential for the release of viral particles from the surface of infrected cells
- Removes sialic acid from glycoproteins
What is the infection mechanism?
Infects the mucous membrane of respritory tracts
- Haemagglutinin binds to sialic acid presen on the cell surface
- Binding stimulates the cell to engulf the viral particles
- Viral particle makes use of cellular processes e.g. translational apperatus to produce its proteins and replication apperatus to make more copies of itself
- New viral particles are released when neuroaminidases cuts of the oligosaccharides (cell not killed)
- Infect new cells
- Released viral particles are spread by areosols, with symptoms appearing 1-4 days after inhaling infected droplet
What are the symptoms of influenza?
- 2-7 low grade fever
- Cough and sore throat
- Chills, fatigue, fever, general aching
- ~20-30% asymptomatic but act as disease reserviors
What is the recovery from influenza like?
Normally rapid and spontaneous recovery
Problems arise due to secondary infections e.g. streptococcus pheumoniae infection
Deaths from secondary infections are usually those who are in the ‘at risk’ group
Normally influenza is seasonal and is classed as an epidemic in this country
How does Rimantidine work?
- Inhibits viral replication by blocking the M2 H+ channel which leads to coating of the virus which means the infectous process is incomplete
How does Timiflu work?
- It contains the oral prodrug Oseltamiviir phosphate
- Oseltamivir is metabolised to the active free Carboxylic acid form in the liver
- It acts as an neuroaminidases inhibitor and prevents release of the virus
What is wrong with timiflu?
How can this problem be solved?
- Oseltamivir is becoming widespread resistant due to antigenic drift:
- variations in viruses due to mutations in genes encoding for antibody-binding sites
- Particualry H1N1 strain
- ALternatively Zanamivir (Relenza) is being used against the H1N1 strain. Used as a powder fo inhaltion. Neuroaminidase inhibitro
What are the problems with vaccines
Influenza is gentically fluid. The genome has 8 short segments of RNA. The number of proteins encoded is unlcear - at least 8 but up to 13 or 14
What factors contribute to genetic variation?
- Drift - small mutations e.g. single point which dont cause much of a problem
- Antigenic shift - when 2 or more strains recombine genes - poses a problem for immune system as these are effectively new strains
