Micro - Influenza Flashcards
What key thing distinguishes influenza from other RT viruses?
Antigenic diversity
Influenza is (enveloped, nonenveloped) (segmented, nonsegmented) (RNA+, RNA-, DNA)
Enveloped segmented (reassortment!) RNA-
What determines an influenza type (A vs. B vs. C)?
Nucelocaspid and matrix proteins
What determines the subtype of influenza A?
HA and NA
What is unique about influenza C vs. influenza A/B?
It is usually asymptomatic, only has 7 genome segments (lacks NA gene)
Most important way to reduce mortality/morbidity of influenza?
Yearly vaccination
What is the role of HA?
Binds sialic acid on mucus membrane layer of respiratory tract –> virion
ATTACHMENT and PENETRATION
Why the name “hemagglutinin”?
Sialic acid also on RBCs, so influenza causes clumping of RBCs
Two sections of HA?
Antigenic domain and receptor binding sites
What quality of HA contributes to rapid evolution of influenza?
Frequent amino acid substitution
What does NA do?
Cleaves neuraminic acid to uncover sialic acid so HA can bind to it; once released from host cell, NA cleaves HA-sialic acid bond so virus can spread
What role does M2 play in virulence?
Ion channel on influenza A only that allows H+ influx into endosome which lowers the pH and causes protein dissociation = UNCOATING
What role does NS1 play in virulence?
Interferon antagonist and inhibits host cell mRNA processing
Genome of influenza A&B vs. influenza C
A&B = 8 segments C = 7 segments (lacks NA; maybe this is why it's not as virulent?)
Replication of influenza vs. paramyxoviruses
Influenza - nucleus
HSV, hPIV, hMPV - cytoplasm
What causes new pandemic strains of influenza?
Reassortment of influenza A genes in a cell co-infected with animal and human strains –> new strain infects human with no immunity
Main influenza A reservoir
Avian
What’s unique about avian influenza A?
It infects respiratory and GI tracts = can be passed in bird poo
What’s unique about swine influenza A?
Avian influenza can’t directly infect humans, but swine can be infected with avian and human strains –> reassortment –> new viruses
2 consequences of influenza A populating human and animal species
- Reassortment –> new pandemic viruses
2. Animal reservoir –> keeps virus circulating even when humans aren’t infected
2 reasons influenza is so contagious
- Viral shedding occurs about 1 day before illness onset
2. Viral titers are highest in first 48 hours, before you know you’re sick and take precautions
What causes mortality associated with influenza?
LRT complication, i.e. pneumonia
Three types of pneumonic complications that can result from influenza infection:
- Primary viral
- Combined viral-bacterial (both at same time)
- Post-influenza bacterial pneumonia (after healed)
How can one distinguish primary viral from secondary pneumonia?
- Primary viral pneumonia comes on within 1-4 days; secondary pneumonia comes on 5 days later
- Secondary pneumonia will produce purulent sputum and a productive cough, elevated PMNs, and WBCs on PBS
