Microbiology - Key Influenza Virus Flashcards
What are some key features of an influenza virus?
- Family: Orthomysxoviridae
- Enveloped virus
- Wild type virion has filamentous morphology
- Negative sense segmented RNA genome (8 segments)
What three features does a pandemic flu virus have?
- Novel antigenicity
- Replicate efficiently in human airways
- Transmit efficiently between people
What are the most common subtypes of Influenza A + B viruses?
- Influenza A (H1)
- Influenza A (H3N2)
- Influenza B
What is the natural reservoir for influenza A?
Ducks
What makes bird flu (H5N1) difficult to transmit between humans?
- Virus doesn’t replicate well at cold temperatures of upper airways (32C)
- Better in deeper lung tissue but more difficult to escape
How is a respiratory disease formed from a virus?
Virus is activated by human airway tryptase found in lung tissue
How many RNA segments are there and what are they comprised of?
- 8
- Nucleocapsid protein
- Very prone to mutation
What is Neuraminidase activity (NA) and what is it more prone to?
- Cleaves sialic acid residues allowing exit of virions from host cell
- Disrupts mucin barrier
More prone to antigenic shift
What is haemagglutinin activity (HA) and what is it more prone to?
- Binds sialic acid receptors allowing for virus entry
- Endosomal envelope fusion = release
More prone to antigenic drift
How are virus strains named?
After haemagglutinin activitiy (H) + Neuraminidase activity (N)
What is antigenic drift?
- The accumulation of point mutations (due to error prone RNA polymerases)
- Changes nature of antigen over time
What is antigenic shift?
- The recomninatino of genomic segments of 2 co-infecting flu strains
- Leads to rapid potentially whole antigenic change for a viral strain
- An infrequent event that leads to a novel strain
- Potentially allows exchange of RNA segments between human + animal strains
What is the pathogenesis of the influenza virus?
- Cleavage of influenza HA by clara typtase in lung leads to extended tropism/growth for H5 + H7
What are soem causes for a severe outcome of flu?
- Secondary bacterial pneumonia
- Mutant virus
- Co-morbidity
- Cytokin storm
What are some antiviral for influenza and how do they work?
Amantadine (PO)
- targets M2 ion channel (antagonist)
- Influenza A only (B lacks M2 protein - has BM2 instead)
- No longer recommended due to resistance
Baloxavir
- Polymerase inhibitor (endonuclease)
Oseltamivir (Tamiflu)
- Neuraminidase inhibitor
- Effective against type A + B
- Most widely used
- Oral
Zanamivir
- Neuraminidase inhibitor
- Inhaled
- Relenza = used in pts with underlying respiratory disease
Peramivir
- Neuraminidase inhibitor
- IV
- Only effective if <48hrs after infection
