SM L3

Question 1

Symptoms of Influenza

Answer 1

Begin 24-48hr after infection, chills
Fever for a few days (38-39 o C), headache, fatigue due to cytokine release
Aches and pains, nasal congestion, irritated watery eyes
Nausea and vomiting
Possible complications….. Tissue damage, pneumonia, bronchitis, sinus and ear infections.

Question 2

What type of virus is influenza?

Answer 2

Negative Sense RNA Viruse
Helical Capsid
Enveloped
Belongs to orthomyxoviridae family

Question 3

True or False - Influenza can be divided into 3 types

Answer 3

True. Influenza A, B and C
There is no single genus of influenza, but rather a family of viruses that are divided into different types and subtypes based on their genetic and antigenic properties.

Question 4

Influenza A is divided into subtypes based on which two surface proteins?

Answer 4

H: hemagglutinin (1 Host range: 15)
N: neuraminidase 19. e.g. H5N1

Question 5

Describe Infleunza A

Answer 5

Can infect multiple species
most virulent and most important human pathogen
can be further defined based on serotypes

Question 6

Describe Influenza B

Answer 6

Almost exclusively infect humans; also the seal!
Does not mutate to same degree as influenza A therefore less genetically diverse
1 serotype…..immunity at early age

Question 7

Describe Influenza C

Answer 7

Can infect multiple species, humans, pigs
Severe illness and local epidemic

Question 8

Host Range of Influenza A

Answer 8

Host range: Birds (avian), (Major reservoir) All H & N types Swine Humans Horses Ferrets, Mink Seals, Whales

Question 9

How is influenza transmitted?

Answer 9

Aerosol, close contact

Question 10

What is influenza sensitive to?

Answer 10

Sensitive to pH, heat and solvents.

Question 11

What are the characteristics of Influenza?

Answer 11

100nm…roughly spherical, though filamentous forms do occur (pleomorphic)
Segment genome
single-stranded-sense RNA
Not a single strand of nucleic acid…it consists of 8 pieces of segmented -ve strand RNA (encode 11 proteins)
> 10 genes
overlapping reading frames
helical capsid and envelope
replicates in nucleus

Question 12

Name the proteins that influenza encodes

Answer 12

Proteins (HA, NA, NP, M1, M2, NS1, NEP, PA, PB1, PB1-F2, PB2)

Question 13

Neuraminidase (NA) 19

Answer 13

Glycoprotein found on outside of the viral particle
Enzyme involved in the release of viral particles from cell
These proteins are the target for antiviral drugs

Question 14

Haemagglutin (HA) 1-15

Answer 14

Lectin that mediates binding and entry of the virus to target cells
This protein is a target for antiviral drugs

Question 15

Influenza genome organisation

Answer 15

8 segmented ss Negative RNA genome

Question 16

Influenza Replication Cycle

Answer 16

1. Virus binds via HA to sialic
   acid-lipid/protein on
   susceptible cell & enters
   via endocytosis
2. virus nucleocapsid
   containing the –vRNA
   transported to the
   nucleus
3. -vRNA transcribed to
   complementary viral
   +mRNA via vRNA
   polymerase (PA, PB1,
   PB2)
4. Viral complementary
   +mRNA either
   exported to
   cytoplasm and
   Golgi/ER and
   translated
   OR
   remains in the nucleus.
   PA
5. NP, PA, PB and other
   viral proteins return
   to nucleus and
   induce new –viral
   RNA and
   nucleocapsid PA,
   PB vRNA
   polymerases
6. HA, NA migrate to
   plasma membrane
7. Matrix & NS2 shutoff
   replication deliver
   nucleocapsid to
   plasma membrane
   M
8. Virus
   assembles and
   buds from cell
   Host cell dies!

Question 17

Why are RNA viruses prone to error?

Answer 17

The replication machinery of RNA viruses is error
prone, giving rise to variation.
Enveloped viruses are more tolerant to mutation than
non-enveloped viruses (Plasticity), as the capsid has to
perform a variety of functions which can not be
compromised
Two mechanisms
Antigenic drift and shift

Question 18

What are the two mechanisms to antigenic variation?

Answer 18

Antigenic drift and shift

Question 19

Antigenic Drift

Answer 19

Antigenic Drift= Appearance of virus with minor
changes in antigen structure

Accumulation of
mutations that
facilitate evasion of
the host immune
response
Absence of RNA
proofreading
enzymes
vRNA polymerase
1/10,000 mutation rate

Question 20

Antigenic Shift

Answer 20

Antigenic Shift= Appearance of virus with major
changes in antigen composition

• Occurs after viruses with
  segmented genomes co
  -
  infect and exchange
  components. * Occurs in areas with high
  numbers of pigs, birds and
  people. e.g. parts of Asia. * Sooner or later, a
  recombinant strain as lethal
  as the 1918 one will appear.

Question 21

When does antigenic shift occur?

Answer 21

• Occurs after viruses with
  segmented genomes co
  -
  infect and exchange
  components. * Occurs in areas with high
  numbers of pigs, birds and
  people. e.g. parts of Asia. * Sooner or later, a
  recombinant strain as lethal
  as the 1918 one will appear.

Question 22

Name the four different flu viruses which swine flu is made up of

Answer 22

North American swine influenza,
North American avian influenza,
human influenza, and swine influenza virus typically
found in Asia and Europe –
“an unusually mongrelised mix of genetic sequences.“

Question 23

Sialic Acid Linkages

Answer 23

HA binds to sialic acid (which is attached
to galactose via linkage) on surface of
host cell membranes.
* Humans express a(2, 6) linkage ->infected
by human flu
* Birds express a(2,3) linkage -> infected
by bird flu
* Swine express both sialic acid link types -
>can be infected by both human and bird
flu.