Transcript File - hs science @ cchs

Avian and Pandemic Influenza
Kathy Harriman
Minnesota Department of Health
Infectious Disease Prevention and
Control Division
Acute Disease Epidemiology Section
What is influenza?
 An acute respiratory illness resulting
from infection with an influenza virus
 Highly infectious and can spread
rapidly from person to person
 Some strains cause more severe
illness than others
Types of influenza viruses
 Influenza viruses are divided into three
main types: influenza A, B, and C
 A viruses – infect birds and other
animals, as well as humans
 A viruses – source of seasonal
influenza epidemics and all pandemics
 B and C viruses – infect humans only
and do not cause pandemics
Where does influenza A virus
come from?
Human influenza A viruses start as avian (bird) influenza viruses
Migratory
water birds
Domestic birds
Humans
and other
animals
Influenza symptoms
 Sudden onset
 Fever, headache, muscle aches,
severe weakness
 Respiratory symptoms, e.g., cough,
sore throat, difficulty breathing
How influenza spreads
 Spreads easily from person to person
through coughing and sneezing
 Transmitted by:
– inhaling respiratory aerosols containing the virus,
produced when infected person talks, coughs, or
sneezes
– touching an infected person or an item
contaminated with the virus and then touching
your eyes, nose, or mouth
Courtesy of CDC
Seasonal influenza:
minor changes - antigenic drift
 Occurs among influenza A viruses
resulting in emergence of new variants
of prevailing strains every year
 New variants result in seasonal
influenza each winter
 Some years are worse than others –
partly related to degree of ‘drift’
What is an influenza pandemic?
 Influenza pandemics are worldwide
epidemics of a newly emerged strain
of influenza
 Few, if any, people have any
immunity to the new virus
 This allows the new virus to spread
widely, easily, and to cause more
serious illness
What causes a pandemic?
 Pandemics occur when a new
avian influenza strain acquires
the ability infect people and to
spread easily person to person
 This can occur in two ways:
– Reassortment (an exchange of
seasonal and avian influenza
genes in a person or pig infected
with both strains)
– Mutation (an avian strain
becomes more transmissible
through adaptive mutation of the
virus during human avian
influenza infection)
Pandemic influenza:
major changes - antigenic shift
 Major changes occur in the surface antigens
of influenza A viruses by mutation or
reassortment
 Changes are more significant than those
associated with antigenic drift
 Changes lead to the emergence of
potentially pandemic strains by creating a
virus that is markedly different from recently
circulating strains so that almost all people
have no pre-existing immunity
Seasonal vs. pandemic influenza
 Pandemic influenza is not just a “bad flu,” it is a wholly
new threat to humans
 A severe pandemic would cause social disruption unlike
anything most persons now alive have ever experienced
 Compared to seasonal influenzas, pandemic influenzas
infect more people, cause more severe illness, and
cause more deaths
 Seasonal influenza viruses most often cause severe
disease in the very young, the very old, and those with
chronic illnesses, but pandemic influenza strains can
infect and kill young, healthy people
 The highest mortality rate in the 1918-19 pandemic was
in people aged 20-40 years
History of influenza
 412 BC - first
mentioned by
Hippocrates
 1580 - first pandemic
described
 1580-1900 - 28
pandemics
Pandemic influenza in the 20th Century
1918 “Spanish Flu” 1957 “Asian Flu” 1968 “Hong Kong Flu”
20-40 million deaths
1 million deaths
1 million deaths
H2N2
H3N2
H1N1
1920
1940
1960
1980
2000
1918 Pandemic
Highest mortality in people 20-40 years of age
- 675,000 Americans died of influenza
- 43,000 U.S. soldiers died of influenza
Lessons from past pandemics
 Occur unpredictably, not always in winter
 Great variations in mortality, severity of illness,
and pattern of illness or age most severely
affected
 Rapid surge in number of cases over brief period
of time, often measured in weeks
 Tend to occur in waves of 6 - 8 weeks,
subsequent waves may be more or less severe
Key lesson – unpredictability
Why is there concern about an
influenza pandemic now?
 A highly pathogenic avian influenza strain
(A/H5N1) emerged in Hong Kong in 1997,
reemerged in birds and humans in 2003, and is
now circulating widely in birds in many countries
 Since 2003, this strain has spread from birds to
humans and as of August 23, 2006 has infected
241 people (141 deaths) in 10 countries
 This strain has also been documented (rarely, so
far) to spread from person to person
 Reassortment or mutation could allow this strain to
become easily transmissible between humans –
there is no way to know if or when this will happen
Would the next pandemic be severe?
 We just don’t know
 However, past pandemics
provide clues as to how
humans may be affected by
a new influenza virus and
how societies would react to
a pandemic
 Information from past
pandemics is used in
economic and disease
models to predict the impact
of future pandemics
What could happen during an
influenza pandemic?
 In the United States, up to 1.9 million
people could die, up to 9.9 million could
be hospitalized, and up to 90 million
could become ill
 Intense pressure on healthcare
 Disruption to many aspects of daily life
Emergency hospital, Camp Funston, Kansas 1918
Courtesy of National Museum of Health and Medicine
Pandemic waves
Past experience teaches us that following
the emergence of a new pandemic virus:
 More than one wave of influenza is likely
 Waves typically last 6-8 weeks
 Gaps between the waves may be weeks or
months
 A subsequent wave can be worse than the first
What can be done to slow
the spread of a pandemic?
 Vaccine:
– not expected to be available until later in a pandemic
 Antivirals:
– likely to be insufficient quantities, effectiveness
unclear
 Disease containment measures:
– may be the only measures available in the early
stages of a pandemic
– may be helpful in slowing the spread of a pandemic,
allowing more time for vaccine production
Vaccine
 Because the virus will be
new, there will be no
vaccine ready to protect
against pandemic influenza
at the start of a pandemic
 Specific vaccine cannot be
made until the virus strain
has been identified and will
take at least 4-6 months to
produce
Antiviral drugs
 Likely to be the only major
medical countermeasure
available early in a pandemic
 Uncertainty about effectiveness
for treatment or prevention
 U.S. goal is to stockpile enough
antiviral drugs to treat 25% of
the U.S. population
Reproduced with permission from Roche Products Ltd. Tamiflu ®
Disease containment measures
 Isolation: restriction of movement/separation of ill
infected persons with a contagious disease
 Quarantine: restriction of movement/separation of
well persons presumed exposed to a contagious
disease
 Self-shielding: self-imposed exclusion from
infected persons or those who may be infected
 Social distancing: reducing interactions between
people to reduce the risk of disease transmission
 Snow days: days on which offices, schools,
transportation systems are closed or cancelled, as if
there were a major snowstorm
Other methods to reduce transmission
 Hand hygiene (cleaning hands with soap and
water or an alcohol-based hand rub)
 Respiratory hygiene, e.g., “Cover your cough”
 Cleaning and disinfection of contaminated
objects, surfaces
 Physical barriers (e.g., glass or plastic
“windows” to protect front desk workers)
 Use of personal protective equipment (PPE) in
some settings (e.g., healthcare) such as
gowns, gloves, eye, and respiratory protection
Employees of Stewart & Holmes Wholesale Drug Co. Seattle, 1918
Courtesy of Grace Loudon Mc Adam
Summary
 The currently circulating avian influenza
strain may or may not cause a pandemic
 Global surveillance is essential;
international cooperation is critical
 Planning for a possible pandemic is
occurring nationally and internationally
 National, state, local, and individual
preparedness are all important
Additional avian and pandemic
influenza information
 MDH
http://www.mdhflu.com
 CDC
http://www.cdc.gov/flu/avian/ index.htm
 HHS
http://www.pandemicflu.gov/
http://www.hhs.gov/pandemicflu/ plan/
 WHO
http://www.who.int/csr/disease/ avian_influenza/en/index.html
Questions?