Influenza Viruses

Question 1

Classify influenza

Answer 1

Orthomyxoviridae

1) segmented
2) - ssRNA
3) Three types: A, B, and C

Question 2

How is Type A influenza characterized?

Answer 2

Based on hemagglutinin (HA) and neuraminidase (NA) antigens

Question 3

Function of hemagglutinin?

Answer 3

virion attachment/entry

antigenic domain for receptor binding sites

**lots of AA substitutions = different flu strains

Question 4

Function of neuraminidase?

Answer 4

Recepter-destorying enzyme (sialic acid) for virion release

*target for anti-viral drugs

Question 5

Function of M2 protein?

Answer 5

Ion channel involved in uncoating of the virus and regulates viral assembly

**only on Influenza A

Question 6

Which drugs target M2?

Answer 6

Amantadine and Rimantadine

Question 7

Function of NS1?

Answer 7

IFN antagonist

–Down regulates host mRNA processing

Question 8

What is the genome structure of inf. A and B?

How is C different?

Answer 8

A/B have 8 segments.

C has only 7 (lacks NA gene)

Question 9

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?

Answer 9

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.

Question 10

What are some Influenza A reservoirs?

Answer 10

Avian, human, swine, horses, seals, whales

Question 11

What is important about birds being an Inf. A reservoir?

Answer 11

1) virus spread by poop

2) allows reassortment or the virus and serves as an extra-human reservoir

Question 12

What are the Inf. B/C reservoirs?

Answer 12

Mainly Humans

Question 13

When is someone most contagious?

Answer 13

The initial onset of sickness.

• -Viral shedding occurs 1 day before illness, peaks 48 hours after infection.
• -little shedding after 6-8 days

Question 14

When does flu become a very serious infection?

Answer 14

When it infects the lower respiratory tract

Question 15

Whats the most serious and common complication from the flu?

Why?

Answer 15

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

Question 16

Is flu bad in pregnancy?

Answer 16

Yes. Can cause fetal loss and/or defects, especially in 2nd and 3rd trimesters.

Question 17

How are elderly people different with the flu?

Answer 17

1) Longer viral shedding times + more at risk for complications
2) Less typical symptoms and lower fevers (bad sense it can mask the illness)

Question 18

How are kids at risk from flu?

Answer 18

Less developed immune systems = risk of pneumonia, meningitis, and encephalitis

Question 19

How does viral pneumonia present?

Answer 19

Typical flu-symptoms followed by increased dyspnea, tachypnea, and hemoptysis

If purulent sputum present, then there is a bacterial infection as well

Question 20

When does flu commonly present?

Incubation period?

Answer 20

Winter and early spring seasons.

Incubation period is about 2 days

Question 21

Which flu type has the most antigenic variation?

Answer 21

Influenza A

–undergoes antigenic drift and shift more often

Question 22

How is flu illness diagnosed?

Answer 22

Rapid antigen test (swab)
–Finds if type A or B

RT-PCR

Question 23

Whats the best way to prevent getting the flu?

Answer 23

Vaccine! Every year

• -inactivated vaccine (Fluzone, IM shots), 6mo or older
• -Live attenuated (FluMist), males and non-prego females from 2- 49 yo

Question 24

MoA of amantadine and rimantadine?

Answer 24

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

Question 25

MoA of Zanamivir (Relenza) and Oseltamivir (Tamiflu)?

Answer 25

Neuraminidase inhibitors

• -prevent viral release and spread
• -good versus Inf. A and B