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Avian and Pandemic Influenza
Kathy Harriman
Minnesota Department of Health
Infectious Disease Prevention and
Control Division
Acute Disease Epidemiology Section
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
What is influenza?
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
Migratory
water birdsDomestic birds
Where does influenza A virus
come from?
Humans
and other
animals
Human influenza A viruses start as avian (bird) influenza viruses
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
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
1920 1940 1960 1980 2000
H1N1 H2N2 H3N2
1918 “Spanish Flu” 1957 “Asian Flu” 1968 “Hong Kong Flu”
20-40 million deaths 1 million deaths 1 million deaths
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
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 illinfected 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
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