Block 3 MICRO Exam -- Influenza (#7)
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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 - 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