Training Kit for

1
Training Kit for Pandemic Influenza
Unit 1 - Background Information
Prepared by Infectious Disease Control Training
Centre, Hospital Authority Infection Control
Branch, Centre for Health Protection, Department
of Health

2
By the end of this unit, you will be familiar
with
Objectives

• the differences between human and avian influenza
• emergence of H5 influenza A virus as a potential
  pandemic virus
• what is a pandemic

3
Influenza virus

• Orthomyxoviridae
• 2 major antigenic glycoproteins
• Haemagglutinin (HA) (H1-16)
• Neuraminidase (NA) (N1-9)
• Antigenic Drift
• Change of genetic material due to lack of
  proof-reading during replication
• Responsible for annual epidemic
• Antigenic Shift
• reassortment and merging of genetic materials
  from different influenza strains
• ?novel viral subtype, most human lack immunity
• Responsible for pandemics

4
Influenza A H5N1 Virus
H5N1 is of particular concern
Haemagglutinin
Neuraminidase

• Mutates rapidly
• Acquire genes from flu strains in other species
• Highly pathogenic in humans
• Birds, if surviving the infection, excrete the
  virus for 10 days, orally and in feces

Single-strand RNA with 8 gene segment
The H5N1 Virion
5
Human Influenza

• Subtypes A(H1 - H3), B
• Droplet transmission
• Typical Incubation period 24 days, with an
  average of 2 days
• Symptoms
• Fever, headache, myalgia, running nose, cough,
  sore throat. Usually subside in 2 7 days

6
Human diseases caused by purely avian influenza
viruses (without prior re-assortment with human
virus) (from WHO website, accessed on 7 Jan 2009)
Emergence of H5 Influenza
7
The Species Barrier
Influenza A H5N1 Virus
Pigs Avian flu in pigs are particularly worrisome
as they possess bird flu and human flu receptors.
They act as a reservoir for genetic reassortment
for flu virus
Chicken New to H5N1 virus Invariable fatal when
attacked
Birds and Water Fouls (e.g. Ducks,
geese) Natural carrier of avian flu, can be
symptomatic or asymptomatic
Human
Feline (Cats, Tigers and Leopards)
8
How can the species barrier be broken?
Influenza A H5N1 Virus
Method 1
H5N1 virion
Mutation
Mutation
Affect several mammalian species include felines,
pigs, and human
Affect water fouls wild birds
Affect domestic poultry like chicken
9
How can the species barrier be broken?
Influenza A H5N1 Virus
Method 2
Avian Flu
Human Flu
Reassortment
It is important to remember that H1 H3 viral
subtypes are prevalent in pigs
10
What is Pandemic

• Endemic
• stable pattern of occurrence of the disease.
• Epidemic
• occurrence of the disease greatly in excess of
  the expected rate.
• Pandemic
• worldwide spread of a disease, outbreaks or
  epidemics occurring in many countries in most
  regions of the world

11
Previous FLU Pandemics
What is Pandemic
12
What is Pandemic

• Pandemic

Health care system rapidly overburdened
Social Disruption Panic
13
Prerequisites for the start of an influenza
pandemic
What is Pandemic

• Emergence of new Haemagglutinin subtype of
  influenza A virus
• General population have no or little immunity
• Cause human disease in a high proportion of
  people infected
• Efficient human to human transmission

14
Progression of pandemic
What is Pandemic
Sporadic cases No human-to-human transmission
Clusters of cases Inefficient human-to-human
transmission
On-going cluster related transmission Substantial
pandemic risk
Pandemic
15
End of Unit 1