Download Preparing for the Next Influenza Pandemic

Preparing for the
Next Influenza Pandemic
Oct 19, 2005
W. David Colby, MSc, MD, FRCPC
Acting Medical Officer of Health
Chatham-Kent
Influenza
• A small and simple virus
• Like all viruses, not a living thing
• A hollow lipid ball studded with
two surface proteins containing 8
RNA gene segments
• Induces living host cells to
manufacture more virus particles
Human Flu
• Fever, chills, cough and myalgia
• Lasts 3-5 days
• Usually a minor illness in the young
and healthy
• Often fatal in the elderly and those
with cardiorespiratory disease
• The flu is not vomiting and
diarrhoea!
Influenza viruses
• Three kinds: A, B and C
• B and C infect only humans and
have never caused pandemics
• Influenza A is naturally found in
the gut of aquatic birds like ducks
• A can infect poultry, swine, horses
and humans
Influenza Surface Proteins
• Hemagglutinin:
 15 subtypes (1, 2, 3…)
• Neuraminidase:
9 subtypes (1,2,3…)
New Influenza Strains:
Usually Arise in China
• Antigenic Drift: Point mutations in the
genes that code for the surface proteins
HA and NA. Minor antigenic variations
from year to year within same HA/NA
types.
• Antigenic Shift: When two different
viruses infect one host cell, their genes
can mix and produce a different HA/NA
type. Major antigenic variation:
 Pandemic!
Pandemic Human Influenza
Strains of the 20th Century
• 1918 H1N1, the Spanish Influenza
-killed 40 million in 1918-1919 season,
more than WW1
-50 X more lethal than most strains
2.5-5% mortality
-especially deadly in young & healthy
• 1957 H2N2, the Hong Kong Flu
• 1968 H3N2, the Asian Flu
Avian Influenza A
• Can infect all species of birds
• Until recently, it was thought that avian
strains could not infect humans…
• 1997: 18 people were infected with an
avian H1N5 in Hong Kong, six died
• 2003-2004: H1N5 widespread in Asian
poultry, >30 human deaths in Vietnam
and Thailand
• Risk factor: close contact with poultry
Avian Influenza A
• Wave of H1N5: 16 cases June-Sept 2004,
13 died (4 in 2005, all young)
• Has spread to China, Indonesia,
Cambodia, Malaysia and Viet Nam
• H7N7, H7N3 and H9N2 have also caused
human infections
• April 2004: H7N3 outbreak in Fraser
Valley BC, 19 million birds destroyed, two
human cases (+ 55 suspect)
Portents of Trouble
• The 1918 Spanish Influenza (H1N1)
gene sequence has been recovered from
old pathology specimens and from
corpses in permafrost from Brevig
Mission, Alaska
• The 1918 H1 hemagglutinin produces
an intense immune response
• The avian H5 is structurally very close
structurally to the 1918 H1
• Ongoing technical/logistical problems
Recent Developments
• Canadian Pandemic Influenza Plan
released February 2004
• Human to human transmission of avian
influenza documented September 2004
• As of Oct 14, > 100 human cases, 50%
mortality
• WHO calls emergency meeting
November 11, 2004 to consolidate plans
for pandemic preparedness:
• Now Phase 3
• Domestic ducks excrete, expanded host
range
What Would Probably
Happen in Chatham-Kent?
• 27,000 people would get sick over a
6-12 week period, 3,000 per week
• Each Week, for influenza alone:
-1500 would need medical
assessment and treatment
-32 would need hospital admission
-12 would die
• These are conservative estimates
The Chatham-Kent Public
Health Unit
• We are planning
• Prevention: influenza vaccination
education, infrastructure
• Reactive: drug prophylaxis,
coordinate with health care sectors
and C-K Municipality (stress on
hospitals, physicians, coroners will
be immense)
• Leadership