Influenza Viruses Flashcards
1) Know structural differences and replication strategies of the flu versus other viruses 2) Know the basis and significance of antigenic diversity of the flu 3) Know the names and MoA for antiviral drugs for flu 4) Know diseases/complications the flu causes
Classify influenza
Orthomyxoviridae
1) segmented
2) - ssRNA
3) Three types: A, B, and C
How is Type A influenza characterized?
Based on hemagglutinin (HA) and neuraminidase (NA) antigens
Function of hemagglutinin?
virion attachment/entry
antigenic domain for receptor binding sites
**lots of AA substitutions = different flu strains
Function of neuraminidase?
Recepter-destorying enzyme (sialic acid) for virion release
*target for anti-viral drugs
Function of M2 protein?
Ion channel involved in uncoating of the virus and regulates viral assembly
**only on Influenza A
Which drugs target M2?
Amantadine and Rimantadine
Function of NS1?
IFN antagonist
–Down regulates host mRNA processing
What is the genome structure of inf. A and B?
How is C different?
A/B have 8 segments.
C has only 7 (lacks NA gene)
1) What is reassortment of gene segment after co-infection of cells by two different HUMAN influenza viruses called?
2) Same thing, but one is a human virus and the other is from an animal?
1) Antigenic drift (minor point mutations)
2) Antigenic shift (major changes, leads to pandemics)
**always reassortment of same TYPE of influenza. A and B types cannot reassort.
What are some Influenza A reservoirs?
Avian, human, swine, horses, seals, whales
What is important about birds being an Inf. A reservoir?
1) virus spread by poop
2) allows reassortment or the virus and serves as an extra-human reservoir
What are the Inf. B/C reservoirs?
Mainly Humans
When is someone most contagious?
The initial onset of sickness.
- -Viral shedding occurs 1 day before illness, peaks 48 hours after infection.
- -little shedding after 6-8 days
When does flu become a very serious infection?
When it infects the lower respiratory tract
Whats the most serious and common complication from the flu?
Why?
Pneumonia
It can cause a secondary bacterial pneumonia (super-infection) by inhibiting the function of the mucociliary escalator
**Strep pneumonia most common; S. aureus and H. influenza also seen
Is flu bad in pregnancy?
Yes. Can cause fetal loss and/or defects, especially in 2nd and 3rd trimesters.
How are elderly people different with the flu?
1) Longer viral shedding times + more at risk for complications
2) Less typical symptoms and lower fevers (bad sense it can mask the illness)
How are kids at risk from flu?
Less developed immune systems = risk of pneumonia, meningitis, and encephalitis
How does viral pneumonia present?
Typical flu-symptoms followed by increased dyspnea, tachypnea, and hemoptysis
If purulent sputum present, then there is a bacterial infection as well
When does flu commonly present?
Incubation period?
Winter and early spring seasons.
Incubation period is about 2 days
Which flu type has the most antigenic variation?
Influenza A
–undergoes antigenic drift and shift more often
How is flu illness diagnosed?
Rapid antigen test (swab)
–Finds if type A or B
RT-PCR
Whats the best way to prevent getting the flu?
Vaccine! Every year
- -inactivated vaccine (Fluzone, IM shots), 6mo or older
- -Live attenuated (FluMist), males and non-prego females from 2- 49 yo
MoA of amantadine and rimantadine?
Inhibit the M2 ion channel (prevents viral uncoating)
- -reduces viral replication and duration of symptoms
- -only effective for Inf. A, but not on H3N2 and H1N1 strains
MoA of Zanamivir (Relenza) and Oseltamivir (Tamiflu)?
Neuraminidase inhibitors
- -prevent viral release and spread
- -good versus Inf. A and B
