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44 Cards in this Set

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How many types of influenza are there?
3
A,B,C
What type of influenza is most severe?
Type A
"Incubation period" for influenza
1 - 3 days
Potential complications of influenza
Primary influenza pneumonia (rare)
Secondary bacterial superinfection/pneumonia (more common)
When is flu season?
Late Fall, Winter, Early Spring
What was particularly unusual about Spanish Flu Pandemic?
Severe illness and excess mortality in healthy young adults
How does influenza enter cells?
Receptor-mediated endocytosis
How many gene segments does influenza have?
8
What does influenza bud through?
Host cell plasma membrane
What 3 proteins are on influenza's surface?
Hemagglutinin
Neuraminidase
M2
Characteristic of HA in infectious virions
Has a "nick" that allows conformational change @ low pH
Function of M2 protein
Acts as an ion channel
Allows H+ ions into endosome

Low pH allows viral RNA to separate from M1 and shell
Inhibiting M2 would suppress what?
Viral replication
Function of M1 protein
Provides structural integrity
Underlies the lipid membrane
Attached to viral RNA

This attachment is compromised at low pH
Function of NP protein
Covers RNA, protecting it from degradation
Contains NUCLEAR LOCALIZATION SIGNAL
Where does influenza replication occur?
In the nucleus
Function of viral transcriptase complex
Made of PA, PB1, PB2
Initiate viral transcription in the nucleus
Function of NS1 protein
Regulates splicing of mRNA

Inhibits actions of interferons made in response to infection
(sequesters dsRNA)

NOTE: this is NOT found in the virion
Made ONLY in infected cells
HA recognizes this to be able to bind to cells
Sialic acid
What is "cap snatching"
Influenza uses caps cleaved from 5' ends of host cell pre-mRNAs (NOT cRNA)

Caps are used to prime synthesis of viral-pre-mRNAs
Caps prevent mRNA degradation
Where (location in cell) does HA get its "nick"?
In the Golgi network
What cells does influenza primarily infect?
Ciliated epithelial cells

These cells contain protease required for HA nicking
Type(s) of influenza that can undergo antigenic SHIFT
Type A only
What is antigenic shift?
When a type A strain is suddenly replaced by a new strain

Antigenically different HA (sometimes NA also)

Shifted virus represents a new subtype
In what intervals are shifts observed?
Every 10 - 40 years
Shifts are associated with pandemics
How many subtypes of type A influenza are there?
At least 3
H1N1, H2N2, H3N2
Why are antigenic shifts associated with severe, widespred infection?
Population lacks neutralizing Abs
How do antigenic shifts occur?
When RNA segments are exchanged between viral strains in secondary host
Type(s) of influenza that can undergo antigenic DRIFT
BOTH types A and B
What is antigenic drift?
Accumulation of mutations in HA that result in inefficient Ab binding
Where do antigenic drift mutations accumulate?
Near the HA binding cleft for sialic acid
NA inhibitors are effective against what types of influenza?
BOTH types A and B

Ex. Oseltamivir
M2 blockers are effective against what types of influenza?
ONLY type A

Ex. Amantadine
How is influenza transmitted
As an aerosol
This is associated with pandemics
Antigenic SHIFT
This is associated with epidemics
Anitgenic DRIFT
Why are swine good "mixing vessels"?
Have receptors for both human and avain viruses
Type of vaccine for influenza
Killed

NOTE: egg-grown
Primary virus responsible for bronchiolitis
Respiratory Syncytial Virus
% of people infected with RSV by age 2
> 95%
Incubation period for RSV
2-8 days
Bronchiolitis syndrome key points
Cough, wheeze, tachypnea, rales
Chest wall retractions

CXR showing hyperinflation, atelectasis
Otitis media in up to 30% of cases

Peribronchiolar inflammation
Epithelial necrosis
Bronchiolitis can cause this in immunocompromised
Giant cell pneumonia

NOTE: this can also be caused by measles
Anti-viral agent used against RSV
Ribavirin