Lecture 12- Influenza

Question 1

Influenza

Answer 1

Ubiquitous in humans
common cause of illness and death
-causes epidemics and threats of pandemics
-large social/financial impact

Question 2

Types of Influenza

Answer 2

Orthomyxoviridae
-Influenza A, B and C

C not common

Question 3

Structure of Influenza

Answer 3

single stranded RNA - sense virus. RNA is segmented, allows to unrelated RNA segments to SHARE genetic material.

-Envelope derived from host cells, studded with glycoproteins that allow in/out of cells

Question 4

Influenza A

Answer 4

A bird virus
Humans are ‘incidental’
-lots of subtypes based on different surface glycoproteins (haemagglutinin and neuraminidase)
-strains named by H & N type + place/year

A/H1/N1/Mexico City 2009

Question 5

Influenza B

Answer 5

a human virus (only human-human)
NO subtypes
- only 1 type of hemagglutinin and neuraminidase
-strains named after year & place of origin

Question 6

Hemagglutinin (H)

Answer 6

Glycoprotein on influenza cell membrane

-allows for the binding/attachment to sialic acid, allowing entry into cell

Question 7

Neurominidase (N)

Answer 7

Glycoprotein on influenza cell membrane.
- cleaves H from sialic acid, allowing exit from host cell. (otherwise it would get stuck), now virus is free to go infect other cells

Drugs against: only useful early on.

Question 8

What strains of influenza are currently circulating

Answer 8

2 A strains
AH1N1: ‘spainish flu’, countless death, young died eldery protected (had immunity).
AH3N2

1 B strain

these are SEASONAL (flu season is winter)

Question 9

Seasonal difference of influenza

Answer 9

little to none in summer. (nothing circulating)

Big peaks in winter

Question 10

Recovery from influenza results in immunity… But then how do we get further infection & epidemics every year

Answer 10

immunity only lasts a few years. The flu virus doesn’t ‘proof read’, virus mutates enough to be sufficiently different. “antigenic drift”, slowly changing over time. ABs formed against H are ineffective if the virus changes enough. This mainly occurs with hemagglutinin.

Influenza A & B are ALWAY undergoing antigenic drift.

Question 11

Frequency of Influenza attacks

Answer 11

kids:3-4 years (decreased memory)

Adults : 8 years

Question 12

Antigenic drift

Answer 12

continuous minor changes in antigens. Leads to repeated infection with AH1N1, A H3N2 and influenza B

Question 13

Pathology of Influenza

Answer 13

kills cells ‘cytopathic’ . Cells always regenerated

Question 14

There is a very short incubation period (one day) before viral production peaks at day two. therefore fast infection/transmission in flu. How does the correlate with INF-a

Answer 14

INF-a released by lymphocytes and NK cells to try fight infection, peaks around day 1-2, when viral load is highest, and is the thing that causes the bulk of bad flu symptoms

Question 15

Flu Virus transmission

Answer 15

Droplet spread
-coughing, sneezing, talking
-requires close contact bc droplets dont’ remain suspended in air
Contact spread (can remain viable on a smooth surface for 24hrs, not infectious once dried)

Question 16

You can reduce the symptoms by half a day if you use certain drugs (oseltamivir) within the first 48hrs, why does this often not work

Answer 16

Because people rarely get to the doctor/ address their symptoms in this time.

-used for prevention, in hospital, rest homes etc.

Question 17

Main why of reducing influenza virus. Why is this constantly changing?

Answer 17

Vaccine. changes due to antigenic drift.

Question 18

How is a flu vaccine formed

Answer 18

circulating (H) gene we are worried about is combined with the non-virulent lab strain (H) gene, forming the
“seed virus”
this is then cultivated in chick embryos, inactivated broken, split and washed so you don’t get any virus RNA in the vaccine, just the Haemmaglutinin antigen

Question 19

Trivalent Vaccine

Answer 19

need protection against all 3 strains.
-only need little changes every year

-hard to cover all strains

Question 20

In healthcare, who does vaccinations benefit?

Answer 20

Not only healthcare workers, but also their patients

-reduces death by 2/3

Question 21

Antigenic Shift

Answer 21

When theres an abrupt introduction of a new H or N gene. New A virus comes up.

-flu ! virus leaps from another species to humans and cause diseases = zoonotic flu = bird flu

Question 22

Multiple different H genes out there, but most DON’T have the ability to..

Answer 22

cause disease

Question 23

Pandemic occurs when

Answer 23

an influenza strain emerges with surface proteins completely different from those on the influenza virus that have been circulating for recent decades.
No-one has AB to these, everyone susceptible to illness,.

Question 24

Danger of H2N2

Answer 24

H2N2 disappeared when H3N2 came in at 1968. therefore anyone born post 1968 lacks immunity, if it were to come back ….. PANDEMIC