9-10: Influenza

Question 1

symptoms associated with influenza infection

Answer 1

many non-specific symptoms
- fever, headache, dry cough, sore throat, runny/stuffy nose, muscle aches

diagnosis is difficult

Question 2

influenza A circulation

Answer 2

wild/domesticated birds

then infects humans with new species/subtypes that are permanent

Question 3

subtype

Answer 3

new species/subtypes of a virus
- divided into genetic clades or groups

each subtype has many strains/variants

Question 4

influenza A and B circulation

Answer 4

in humans

Question 5

influenza A: antigenic shift

Answer 5

“mixing” of genes from influenza viruses

caused pandemics from antigenic shift in animal reservoir and then widespread human infections

Question 6

influenza B: antigenic drift

Answer 6

accumulation of a series of minor genetic mutations

drift is generally linear

well-adapted since its only in humans

Question 7

influenza A structure

Answer 7

classic RNA virus
- envelope + envelope proteins

hemagglutinin (H) and neurominidase (N)
- main proteins/antigens on the surface of the virus
- 16 major variants of H, 9 major variants of N
- each major variant with hundreds more subtle variants

Question 8

influenza life cycle

Answer 8

RNA goes and multiples, making new virions which bud and are released

classic and simple
- only infects epithelial cells
- cause most disease in lungs but can spread to the whole body

Question 9

naming of human viruses

Answer 9

type/location/isolate number/year (subtype)

Question 10

naming of viruses with a non-human host

Answer 10

type/host/location/isolate number/year (subtype)

Question 11

strain/isolate number

Answer 11

specific virus obtained from a host

specific to an individual animal/human

Question 12

three types of influenza causing disease in humans

Answer 12

seasonal
- always one annually

pandemic

zoonotic

usually a zoonotic influenza can become a pandemic which evolves to be seasonal

Question 13

seasonal influenza

Answer 13

typically occur during winter in temperate climates

in tropical regions, occurs throughout the year
- closer you are to the equator, the more likely you are to have two peaks

Question 14

flu peaks in Feb for the northern hemisphere

Answer 14

influenza endemic year-round

some infections all the time but epidemic with seasonal influenza every winter

Question 15

hypotheses to why flu is seasonal

Answer 15

people spend more time indoors in close contact

host factors increase susceptibility/transmission

virus persists longer/transmits better in cold dry weather

Question 16

immune response to seasonal influenza A

Answer 16

immune system makes antibodies to the specific version of H and N present on the virus
- main antigen targets
- unique and not common so it is not a PAMP

next flu season, variant viruses have subtle changes to H and N so they evade pre-existing antibodies

Question 17

immune weapons to seasonal influenza A

Answer 17

neutralising antibodies
- IgG and IgA

cytotoxic T cells (CTLs)

both of the above kill infected cells

however, seasonal virus mutates to evade antibodies and CTLs
- need infection or vaccination every few years

Question 18

antigenic drift in seasonal flu viruses

Answer 18

mutations and changes in H/N antigens
- higher mutation rate with influenza than other viruses

antigenic drift occurs within an influenza subtype and an influenza type
- leads to annual/seasonal flu

Question 19

antigenic drift vs. antigenic shift

Answer 19

drift
- same subtype
- point mutations
-causes seasonal flu

shift
- genetic reassortment/exchange of gene segments (two different viruses infecting the same cell allowing genetic reassortment of subunits)
- new subtype
- causes pandemic and can be zoonotic

Question 20

cycles of influenza epidemics/pandemics

Answer 20

caused by antigenic drift/shift

Question 21

1918 flu

Answer 21

caused by influenza A H1N1

> 500 million infections, 20-50 million deaths
- 2.5% case fatality rate

mortality mostly due to secondary bacteria linfections

1919 flu also caused by H1N1 but fewer deaths because everyone had protection (herd immunity)

unusual features
1. three waves of infections (sign of a pandemic/new flu rather than seasonal)
2. high mortality rate killing 18-45 and males disproportionately

Question 22

H5N1

Answer 22

2003

virulent in domestic birds
- changed the world of agriculture

doesn’t spread easily to humans but causes severe disease
- 53% mortality (highest so far)

was going to be the new pandemic

Question 23

new H1N1

Answer 23

2009

first new pandemic influenza infection in 42 years

displacement of old H3N2 and old H1N1

combination of Eurasian and NA swine viruses
- H1N2 that was already a triple reassortment in pigs, Eurasian swine H1N1 from 1918 swine flu
- 6 gene segments from triple reassortment H1N2 and 2 from swine H1N1

not nearly as virulent so lower fatality rate even though it was a brand new pathogen (0.05%)

Question 24

H9N2

Answer 24

2015

no human-human transmission

endemic in domestic birds

Question 25

H5N6

Answer 25

2014

domestic bird outbreaks in winter

very high fatality rate (43%)

no human-human transmission

Question 26

H7N9

Answer 26

2016

no human-human transmission

triple genetic reassortment of three avian flu viruses H7N3, H7N9, H9N2

virus found in respiratory tracts and not just digestive tract