Influenza2005

1
Influenza-2005

• J Barklie Clements
• b.clements_at_vir.gla.ac.uk
• tel [phone]

2
Influenza-Overview

• Clinical
• Molecular biology
• Genetic changes/epidemiology
• Treatment/prevention

3
Clinical
4
Flu-a killer disease
A lengthy senseless war has depleted Europe of
most of its young men and resources. Then a
formerly rather innocuous virus suddenly mutates
into a new killer strain which infects all
corners of the globe, from Alaska to Africa,
within a matter of weeks. This new disease is not
only remarkably contagious, but it is so lethal
and destroys so many lives in such a short time
that even the ghastly global war pales in
comparison The scariest aspect of this tale is
that it is not fiction
5
Flu-the grim reaper
I had a little bird, Its name was Enza. I
opened the window, And in flu enza.
6
Spanish flu 1918-19

• Mortality rate was 2.5 compared to previous
• epidemics of 0.1, ie more than 20x higher
• One anecdote was of 4 women playing bridge late
  into the night. Overnight, 3 died from flu
• Patients "died struggling to clear their airways
  of a blood tinged froth that sometimes gushed
  from their nose and mouth"

7
Transmission by aerosols
8
Pathogenesis

• Spread by aerosols is very efficient
• Primary infection of ciliated epithelial cells
  in upper respiratory tract. Cell killing gives
  toxins that cause the symptoms fever, muscle
  ache, headache, prostration, anorexia
• Normally lasts 3-7 days
• Death from primary infection is rare. Cell
  damage predisposes to secondary bacterial
  infections with deaths, especially in the elderly

9
Replicates in epithelial cellsof respiratory
tract
10
Molecular biology
11
Orthomyxoviruses Gr 'myxa'mucous

• Flu A viruses infect mammals, including man,
• horses, pigs, ferrets and birds, cause epidemics
• and pandemics
• Flu B and C viruses infect only humans are
• not as severe as A types
• Pigs and birds form important reservoirs,
• generating new viruses that infect humans via
• close contact between animals man

12
Virion structure

• Lipid envelope with 2 projecting glycoproteins
  
• haemagglutinin (HA), a trimer
• neuraminidase (NA), a tetramer
• Envelope inner side is lined by
• matrix M1 protein
• Inside are 8 ribonucleoprotein
• genome segments

13
Cell entry

• HA binds mucoproteins on epithelial cells
• containing terminal sialic acid groups
• Binding can be reversed via polysaccharide
• cleavage by NA spikes, preventing the virus being
  
• neutralised by sialic acid in mucous particles

14
Cell recognition uncoating
15
Flu-uncoating in endosomes
16
Influenza-membrane fusion summary
viruses engulfed by endosomes are acidified
there. Ion channels of viral M2 protein allow
import of H ions inside. At pH 5.0, the HA
monomers are cleaved by a trypsin like enzyme at
the base of the 'stem' into HA1 and HA2
polypeptides (linked by disulphide bonds)
cleavage causes a conformational change in HA
which activates a membrane fusion function in
HA2. Close proximity of the virus envelope
endosome membrane with HA2 results in fusion of
the two membranes, passage of the nucleocapsid
into the cytoplasm

17
Each RNP segmentcontains
18
8 genome segments (-)RNA encode 10 proteins

• Segment Proteins Functions
• 1 PB2 Polymerase mRNA cap
  binding
• 2 PB1 Polymerase elongation
• 3 PA Polymerase protease
  activity
• 4 HA Major antigenic
  glycoprotein
• NP Nucleoprotein virus RNA
  binding
• 6 NA Virus release
• 7 M1 Matrix major virion
  component
• M2 Membrane
  protein, forms H ion channel
• NS1 Non-structural
  inhibits cell RNA splicing
• NS2
  Non-structural nuclear export of genomes

19
Replication

• PB2 attaches to the m7G cap of host cell mRNAs
  that is cut from the mRNA by PB1 acts as a
  primer for viral RNA synthesis. PB1 PA then
  complete the synthesis of viral () sense strands
  
• Two classes of () sense RNAs are made
• (a) polyadenylated transcripts for
  translation
• into viral proteins.
• (b) non polyadenylated as templates for
  the
• synthesis of new (-) sense genome
  RNAs

20
Replication-summary
21
Epidemiology
22
Epidemiology

• every 10-15 years worldwide a new
• pandemic strain appears in man with a totally
• new HA sometimes a new NA (antigenic shift)
• this strain then undergoes minor changes
• (antigenic drift) driven by antibody pressure

23
Classification

• 15 HA serotypes
• 9 NA serotypes
• named in the following way
• A SINGAPORE 6 86 (H1N1)
• TYPE
• TOWN first isolated
• NUMBER of isolates
• YEAR of isolation
• TYPE of HA and NA

24
Appearance/reappearanceof pandemic strains
25
Antigenic drift

• reflects, minor mutations in one or more of 4 HA
  regions genome is RNA so mutation rate is high
  single base pair substitutions accumulate that
  evade antibody. Effects are evident over 2-3
  years
• occurs in all A, B and C strains

26
HA showing variable drift regions
27
Antigenic shift-1

• a new HA is acquired (plus sometimes new NA) that
  is crucial for infection cell entry
• exclusive to A strains
• enables flu to cause pandemics

28
Antigenic shift-2

• uses mixing vessels eg pigs that are
  susceptible to both bird human strains.
  Complete genome segments can be exchanged between
  these viruses if they infect the same cell

29
Influenza-species barrier
the species different virus types infect is
due to different forms of sialic acid present on
cellular glycoproteins sialic acid
recognition is determined by the amino acid at
position 226 of haemagglutinin human viruses
amino acid 226leu avian viruses amino acid
226gln
this provides a species barrier between birds
and humans but, pigs provide a "mixing pot" as
can be infected by both virus types, allowing
passage of avian viruses to humans
30
Killer flu coming?

• 1997 a 3 year old boy died in Hong Kong,
• from first flu A subtype H5N1 in
• a human, that causes lethal bird flu,
• decimating flocks of domestic poultry
• The outbreak fizzled out after 6 deaths.
• Why? H5 HA has glutamine at
• position 226 - i.e. is avian and poorly
  adapted
• to humans. But, with a single mutation
• to HA226 leucine (as in human viruses)
• big trouble!

31
Theres more!

• bird H5N1 has killed 40 people resulted
• in the deaths of millions of chickens
• (infection and culling) since Dec 2003
• most humans caught the virus by
• handling poultry not from humans
• the virus is now in pigs with no symptoms,
• bad news as pigs can be infected by
• human viruses potentially creating a
• pandemic virus strain

32
Treatment
33
Treatment-1

• amantidine and rimantadine drugs
• are active against most A strains
• binding M2 protein, their action is due
• to an inability of drug treated cells to lower
  the pH of endosomes causing uncoating, an M2
  function

34
(No Transcript)
35
Treatment-2

• 11 universally conserved amino acids form the NA
  active site. Synthetic sialic acid analogues are
  NA enzyme inhibitors, effective against all A B
  strains
• Hoffman La Roche's Tamiflu, taken in pill form,
  confers decreased severity duration of symptoms
  
• Smith Klines Relenza is inhaled

36
Prevention
37
Vaccines

• are viruses of the required HA type. Large
  amounts are grown in embryonated eggs (cheap and
  efficient) purified and formalin inactivated. The
  vaccine given subcutaneously achieves 60-80
  protection

• TAKES TIME a decision must be made in August as
  to which HA type to use the following winter. A
  monitoring system worldwide helps make this
  decision

38
Influenza-Overview

• Clinical
• Molecular biology
• Genetic changes/epidemiology
• Treatment prevention

39
(No Transcript)
40
Virion structure-2
41
Genetic changes

• Enhance the virus ability to infect the host
  evade the immune system
• Separate genome segments facilitate genetic
  exchange between different strains
• Exchange of genes causes new combinations of HA
  (and NA) to be expressed on the viral envelope
• Both major and minor genome changes occur

42
Genomes are released from acidified endosomes