Flu

1. INFLUENZA
Including avian
Chapter 31
Avian Influenza

2. Influenza
• Febrile respiratory disease with systemic symptoms
caused by a variety of other organisms often called „flu
• Birds, swine, other mammals also affected
• Highly infectious and can spread rapidly from person to
person
• Some strains cause more severe illness than others

3. History of influenza
• 412 BC - first mentioned by
Hippocrates
• 1580 - first pandemic
described
• 1580-1900 - 28 pandemics

4. Types of influenza viruses
• Influenza viruses divided into 3main types: influenza
A, B, and C
• A viruses
• infect birds and other animals, as well as humans
• source of seasonal influenza epidemics and all pandemics
• causes an average 30,000 deaths per year
• Especially dangerous for the elderly
• B and C viruses
• infect humans only and do not cause pandemics
• virus C infections - much milder

5. Influenza
• Mutates frequently
• Antigenic drift: small mutations that require a new vaccine every
year
• Antigenic shift: emergence of new strains (such as H1N1 become
common when H3N2 used to be about the only human influenza
circulating)
• Co-infection with 2 viruses is possible
• Recombination of 2 segments can create a different virus

6. 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

7. Seasonality:
drift
minor changes - antigenic
• influenza in humans is closely tied to seasonal outbreaks,
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typically associated with winter months
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
avian influenza: seems tied to bird migration patterns and
social behavior

8. Transmission
• 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
• 100,000 TO 1,000,000 VIRIONS PER
DROPLET
• touching an infected person or an item
contaminated with the virus and then
touching your eyes, nose, or mouth
• expelled respiratory droplets can
contaminate surfaces, and be
transmitted to mucous membranes
through direct contact
• Avian: handling of infected bird
feces

9. symptoms
• Sudden onset
• both systemic and respiratory symptoms can occur to varying
degrees
• systemic - fever, headache, myalgia, malaise
• respiratory - cough, sore throatdifficulty breathing
• Complications:
• recently some increase in morbidity and mortality - possible factors?
• more elderly people
• more high risk neonates
• more immunosuppressed patients
• bacterial superinfection can be severe
• Streptococcus pneumoniae the most common pathogen involved
• Staphylococcus aureus increasing, especially severe pneumonia due
to MRSA

10. prevention
• Vaccine:
• current CDC guidelines recommend immunizing the elderly,
pregnant women, and high risk patients (health care and lab
workers, immunosuppressed)
• Antivirals:
• E.g Tamiflu : insufficient quantities, effectiveness unclear
• Disease containment measures:

11. 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

12. 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 2 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)

13. 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 preexisting immunity

14. Global response

15. Seasonal vs. pandemic influenza
• Pandemic influenza is not just a “bad flu,” it is a wholly
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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

16. 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

17. 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

19. 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

20. What about an avian influenza pandemic?
• 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

21. Would the next pandemic be severe?
• Past pandemics provide
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clues as to how humans may
be affected by a new
influenza virus and how
societies would react to a
pandemic
Info n from past pandemics
used in economic and
disease models to predict
impact of future pandemics
In US , 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

22. Pandemic waves
Past experience teaches us that following
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

23. What can be done to slow
spread of a pandemic?
• Vaccine:
• “pre-pandemic” H5N1 vaccines are in development, but would
have reduced efficacy in a pandemic due to antigenic drift
• Antivirals
• 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

24. Vaccine
• Because 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 virus strain has
been identified; takes at
least 4-6 months to produce

25. Antiviral drugs
• Likely to be 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 ®

26. Disease containment measures
• Isolation: restriction of
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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

27. 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

28. Global surveillance and planning
• Global surveillance is essential; international cooperation
critical
• International Health Regulations
• Pandemic Alert System
• http://www.who.int/influenza/preparedness/pandemic/h5n1phase/e
n/
• Planning for a possible pandemic is occurring nationally
and internationally
• National, state, local, and individual preparedness are all
important

29. Current WHO phase of pandemic alert for
avian influenza A(H5N1) is: ALERT
•
Alert phase: phase when influenza caused by a new
subtype has been identified in humans. Increased
vigilance and risk assessment, at local, national and
global levels, are characteristic of this phase.
• If risk assessments indicate that new virus is not developing into a
pandemic strain, a de-escalation of activities towards those in
interpandemic phase may occur.