Orthomyxo influenza virus

Question 1

Type

Answer 1

Orthomyxovirus
Roughly spherical
Enveloped
-ve ssRNA
- replicates in
target cell
nucleus
- assembles and
buds from plasma
membrane

Question 2

Transmission
& season

Answer 2

Zoonotic
disease
Reservoir:
birds-wild
ducks
Pigs: genetic
“mixing bowl”
of strains -
coinfection
with 2 strains
- resp droplets
- aerosols
- direct contact
- viral shedding
at onset of
illness 0-24 hrs
Peaks in
November-mar
ch

Question 3

Type A:

Answer 3

8 segments
- Rod shaped
- Current
subtypes in
human: H1N1
and H3N2
viruses
- Bird flu
- Also infect
human and
mammals(swine)
- Epidemic and
pandemic
- All 18 H types
and all 11 N
types found in birds )
Antigenic shift
and drift
Antigen shift:
sudden
reassortment of 8 genetic
subunits- receptors for
both and bird and human
flue

Question 4

Type B

Answer 4

8 segments - Only in
humans(and
seals)
- Less severe
epidemics than
influenza A; no
pandemic
- Antigen drift
only
- 2 lineages:
victoria like,
yamagata like

Question 5

Type C

Answer 5

• 7 segments - Mild illness - No epidemic or
  pandemic
• No subtype - Antigenic drift
  only(less frequent)
  Nomenclature:
  Type/Host of
  origin/Geographic
  origin/Strai number/Year
  of isolation plus antigenic
  description of HA and
  NA(type A only)
  E.g. A/Avian/Hong
  Kong/03/68(H3N3)
  Vaccine lotto
• Effect of the
  vaccine is
  proportional to the genetic
  “match” b/w vaccine strain
  and the epidemic strain

Question 6

Adult sx

Answer 6

1. Abrupt fever, chills,
   severe muscle aches
2. Loss of appetite, non
   productive cough
3. Recovery 7-10 days

Question 7

Child Sx

Answer 7

me as adult sx PLUS:
1. GI sx: vomiting,
abdominal pain
2. Ear pain: otitis media
3. Croup
4. Febrile
convulsions(children
under 3 but rare)
Complications:
- Primary viral
pneumonias
- Secondary bacterial
pneumonias
- Guillain Barre
syndrome
- Encephalitis - Reye syndrome:
fatty degeneration of
liver. DO NOT GIVE
ASPIRIN

Question 8

Pathogenesis

Answer 8

1. Hemagglutinin(HA): binds
   sialic acid & promotes viral entry
   - Activation requires
   cleavage via cellular
   proteases, proteases
   determine tissue
   tropism
2. Neuraminidase: promotes
   progeny virion release
3. M2 protein: A ONLY -protein
   channel→ dec pH → release
   ribonucleoproteins → replication
   in nucleus
4. IFN & cytokines via NK and
   T cells → imp role in immune
   resolution and
   immunopathogenesis
5. Epithelial damage→ local sx
   6.M1 protein

Question 9

Diagnostic

Answer 9

• Detect viral
  antigens: CF,
  EIA, HAI
• Serology: 4x
  rise in antibody
  titers between
  acute &
  convalescent
  phase sera
• detection of
  viral nucleic
  acids via
  RT-PCR or
  hybridization

Question 10

prognosis and prevention

Answer 10

Pts at risk off
other
infections in
those days
Amantadine
and
rimantadine:
block M2 on
type A
Tamiflu;
inhibit
neuraminida
se: without
this, virus
binds to its
own sialic
acid & forms
useless
clumps:
blocking
release
- Influenza A,
B NOT C
Body
develops
immunity to
each
separate H
and N
independent
ly!