L3/4 - Influenza Flashcards
Where does the variation mostly on influenza?
HA segment
What are the 5 criteria for naming influenza?
- Subtype (A/B/C)
- Location
- Number
- Year of isolation
- Information HA/NA
How many HA and NA groups are there?
18 HAs
9 NAs
How much % difference can HAs (and NAs) have?
30%
What animal species can all types of influenza infect?
Birds
How does HA0 make HA1 and HA2?
HA0 is cleaved by cellular proteases
What is the determinant of host range?
Specificity of receptor binding: HA-SA
a2-3 or a2-6 linkages
Which sialic acid linkages do BIRDS and HUMANS have?
Birds: a2-3
Humans: a2-6
PROTECTS HUMANS FROM MANY AVIAN INFLUENZAS
Why is host specificity not so straight forward?
HA proteins can attach to both a2-3 and a2-6
What strains tend to be low pathogenicity ‘seasonal’ flu?
H1, H2, H3
What strains have decimated chicken populations?
H5, H7
240mil chickens culled/died
How do HAs show differenced in their preferred hosts?
ability to cleave the host’s sialic acid
How many virus particles can one sneeze contain?
1,000,000
What are the 2 ways flu is transmitted?
Virus inhalation via respiratory tract
direct contact - fomites
How is direct contact for flu prevented?
Personal hygiene
What are symptoms of influenza mostly due to?
immune response
What is responsible for the different peak months in north/south hemispheres?
Climatic influence of summer and winter
UV exposure
LOW TEMPERATURE
LOW HUMIDITY
Social behaviour - indoor crowding, xmas
What conditions are best for flu transmission?
low temp - 5c
Low humidity - 20-35%
viruses are more stable and increased chance of droplet inhalation
What type of flu was the 1918 Spanish flu?
H1N1
what are the reasons for the severity of the 1918 Spanish flu?
cleavability of the HA protein
The HA protein could be cleaved by OTHER PROTEASES - infect other cells and ORGANS
What is antigenic DRIFT?
RdRP makes errors when copying
1/10000
incorporation of SINGLE NUCLEOTIDE CHANGES
Why are most anitgenic drift changes on HA1?
HA1 has low functional restrictions
most mutations are OUTSIDE THE RECEPTOR BINDING SITE
changes would affect ability of HA to bind to SA in binding site
What is antigenic SHIFT?
2 different flu viruses infect the same cell
RARE EVENT! (PANDEMICS)
How does the pig allow human and avian strains to mix?
both a2-3 and a2-6 linkages
What 4 viruses make up swine flu?
US pig
Eurasian pig
US avian
Human
3 combined
4th virus eurasian swine then combined
What is the barrier between the highly pathogenic H5N1 infecting the human population?
SPECIES BARRIER
What are the 3 requirements for human-human spread of H5 strains?
1) enter cells of human URT
2) replicate in HIGH NUMBERS in URT cells
3) exit URT cells
Can sialic acid binding easily change through mutation?
yes
How many aa changes are required to switch HA specificity?
1 or 2 aa changes
Why is the replication rate of avian H5N1 reduced in humans?
different temperature
37 vs. 41
What mutation in PB2 can affect peak replication temeprature?
E627K
What were the 3 mutations of H5N1 given to ferrets origianlly?
Q222L
G224S
E627K
Why were the 3 original mutations of the H5N1 virus not enough?
NO aerosol transmission
Brief overview of ferret experiment to select an aerosol transmissible virus?
infected with H5N1 (222/224/627)
4 days - sneeze sample
infect
wait 4 days - repeat
x10
(ANTIGENIC DRIFT)
What are the 2 additional mutation to the H5N1 (222/224/627)
H103Y
T156A
How is the influenza vaccine produced?
GISRS predicts 3/4 dominating strains yearly
What is the traditional method of influenza vaccine production?
3 chosen strains - weakened
segment exchange (REASSORTMENT) with PR8
256 genotypes
INFECT EGGS
Which segments are PR8 and which are the circulating strain?
circulating strain - HA, NA
rest - PR8
What are the 3 drawback of tradition flu vaccine making?
SLOW reassortment - 3 months
dependent on eggs (170mil)
some H5N1 grow poor in eggs
What is the ‘new’ way to make flu vaccines?
cDNAs - encode the 8 RNA genome sequences wanted
make 8 functional RNPs
How is the cDNA-based system for vaccines better?
seed in 2 weeks
no eggs
no issues with egg allergy/growing poorly
What are the 3 current targets for anti-influenza therapeutics?
3) Endosome escape
5) RNA synthesis
8) Release
(FLU) What anti-virals are used for (step 3) endosome escape?
The Adamantanes
AMANTADINE
RIMANTADINE
What are the pros/cons of the Adamantanes?
PRO - cheap, effective
CONS - administered before day 2
How is Rimantadine different to amantadine?
added methyl group
What influenza does the Adamantanes work against?
ONLY FluA
How do Adamantanes work?
prevent M2 ion channel activity
blocks/closes pore
cannot exit endosome
What are issues with Adamantanes?
most human flus now resistant
mutations within M2 channel
NO LONGER FDA APPROVED
(FLU) What anti-virals inhibit the endonuclease active site (step 5 - RNA synthesis)
XOFLUZA
How does Xofluza act?
binds the PA endonuclease active site
What flus is Xofluza effective against?
fluA, fluB
What does step 8 virus release involve?
NA
ability of NA to bind to SA and cleave it
(FLU) What anti-virals are effective against (step 8) virus release?
Relenza - ZANAMIVIR (aerosol)
Tamiflu - OSELTAMIVIR (oral)
Repivab - PERAMIVIR (IV)
WORK BY MIMICING SIALIC ACID
BLOCK NA ACTIVE SITE
What is the stockpile of tamiflu and relenza worth?
£500m
What is the issue with flu resistance in NA inhibitors?
NA muatates so it no longer binds to tamiflu/influenza
What are future flu anti-virals not yet FDA approved?
polymerase inhibitor - FAVIPIRAVIR
DAS-181 - HA attachment inhibitor
How do NA inhibitors act?
bind with higher affinity to NA than sialic acid
exploite weak site 2 in the 5 site NA binding pocket
Why do NA inhibitors bind better than SA?
charged guanidino group added - interacts with neg charged Asp and Glu more strongly
100x higher affinity
