S.M Lecture 3 Flashcards
(23 cards)
Symptoms of Influenza
- Begin 24-48hr after infection, chills
- Fever for a few days (38-39 o C), headache, fatigue due to cytokine release
- Aches and pains, nasal congestion, irritated watery eyes
- Nausea and vomiting
- Possible complications….. Tissue damage, pneumonia, bronchitis, sinus and ear infections.
What type of virus is influenza?
- Negative Sense RNA Viruse
- Helical Capsid
- Enveloped
- Belongs to orthomyxoviridae family
True or False - Influenza can be divided into 3 types
True. Influenza A, B and C
There is no single genus of influenza, but rather a family of viruses that are divided into different types and subtypes based on their genetic and antigenic properties.
Influenza A is divided into subtypes based on which two surface proteins?
- H: hemagglutinin (1 Host range: 15)
- N: neuraminidase 19. e.g. H5N1
Describe Infleunza A
- Can infect multiple species
- most virulent and most important human pathogen
- can be further defined based on serotypes
Refer to table in slides
Describe Influenza B
- Almost exclusively infect humans; also the seal!
- Does not mutate to same degree as influenza A therefore less genetically diverse
- 1 serotype…..immunity at early age
Refer to table in slides
Describe Influenza C
Refer to table in slides
- Can infect multiple species, humans, pigs
- Severe illness and local epidemic
Host Range of Influenza A
Host range: Birds (avian), (Major reservoir) All H & N types Swine Humans Horses Ferrets, Mink Seals, Whales
How is influenza transmitted?
- Aerosol, close contact
What is influenza sensitive to?
- Sensitive to pH, heat and solvents.
What are the characteristics of Influenza?
- 100nm…roughly spherical, though filamentous forms do occur (pleomorphic)
- Segment genome
- single-stranded-sense RNA
- Not a single strand of nucleic acid…it consists of 8 pieces of segmented -ve strand RNA (encode 11 proteins)
- > 10 genes
- overlapping reading frames
- helical capsid and envelope
- replicates in nucleus
Name the proteins that influenza encodes
- Proteins (HA, NA, NP, M1, M2, NS1, NEP, PA, PB1, PB1-F2, PB2)
Neuraminidase (NA) 19
- Glycoprotein found on outside of the viral particle
- Enzyme involved in the release of viral particles from cell
- These proteins are the target for antiviral drugs
Haemagglutin (HA) 1-15
- Lectin that mediates binding and entry of the virus to target cells
- This protein is a target for antiviral drugs
Influenza genome organisation
- 8 segmented ss Negative RNA genome
Influenza Replication Cycle
- refer to slides
Why are RNA viruses prone to error?
- The replication machinery of RNA viruses is error prone, giving rise to variation.
- Enveloped viruses are more tolerant to mutation than non enveloped viruses (Plasticity), as the capsid has to perform a variety of functions which can not be compromised
What are the two mechanisms to antigenic variation?
- Antigenic drift and shift
Antigenic Drift
- Appearance of virus with minor changes in antigen structure
Antigenic Shift
Appearance of virus with major changes in antigen composition.
(The geneic change that enables a flu strain to jump from one animal species to another, including humans is called “antigenic shift”)
When does antigenic shift occur?
- Occurs after viruses with segmented genomes co-infect and exchange components
- Occurs in areas with high numbers of pigs, birds and people.
Name the four different flu viruses which swine flu is made up of
- North American swine influenza
- North American avian influenza
- human influenza, and swine influenza virus typically found in Asia and Europe
Sialic Acid Linkages
HA binds to sialic acid (which is attached to galactose via linkage) on surface of host cell membranes.
