Transcript Slide 1

Influenza:
virus, disease, prevention
& control, treatment
Lecture presented by
Dr Ghassan Awar
02 May 2009
Virus
Influenza Virus
Orthomyxovirus
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The Virus
Types of Influenza Virus
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Three types: A, B, C
Influenza Type A can infect: People, birds, pigs,
horses, seals, whales and others
Influenza Type B: Human virus
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Not classified according to Subtype
Cause human epidemics but not pandemics
Influenza Type C cause mild illness in humans
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Not classified according to subtype
Do not cause epidemics or pandemics
Influenza Virus
Types A and B
Type A
(Seasonal, avian, swine
influenza)
Type B
(Seasonal influenza)
Can cause significant disease
Generally causes milder disease
but may also cause severe
disease
Infects humans and other
species (e.g., birds; H5N1)
Limited to humans
Can cause epidemics and
pandemics (worldwide epidemics)
Generally causes milder
epidemics
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Influenza A Virus Subtyping
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Influenza A subtypes are determined by two
surface glycoproteins:
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Hemagglutinin (HA)
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Neuraminidase (NA)
16 HA’s and 9 NA’s
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Species Infected by Influenza A, HA and NA Subtypes
H2
N1
N2
H3
H4
N3
N4
H5
H6
H7
H8
N5
N6
N7
N8
N9
H1
H9
H10
H11
H12
H13
H14
H15,16
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Influenza Nomenclature
Influenza type
Year of isolation
Hemagglutinin subtype
A/Sydney/5/97 (H3N2)
Geographic source
Isolate number
Neuraminidase subtype
Antigenic Drift
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Point mutations in the hemagglutinin gene cause
minor antigenic changes to HA
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Continuous process
Immunity against one strain may be limited
Antigenic drift produces new virus strains that may not
be recognized by antibodies to earlier influenza
strains
One of the main reasons why people can get the flu
more than one time (Seasonal epidemics).
one or two of the three virus strains in the influenza
vaccine are updated:
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6-8 months process
Targeted at high-risk (inactivated)
Antigenic Shift
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new influenza virus that can infect humans and has
(new HA subtype ± NA) through:
 Genetic reassortment (human and animal viruses)
 Direct animal (poultry) to human transmission
if most people have little or no protection against the
new virus:
 Spread easily from person to person
 Pandemic (worldwide spread) may occur
How Do Influenza Viruses Become More
Pathogenic?
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Antigenic Shift
Strong selection pressure acting on
mutations or changes in HA or NA
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Direct infection in humans
Re-assortment
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Two different strains of influenza infect the
same host
“Reassorted” virus emerges
Examples of Re-assortment and
Direct Transmission
Non-human
virus
Human
virus
RE-ASSORTMENT
Reassortant
virus
Epidemiology Terms
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Endemic
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A disease that occurs at an expected constant level in a
population
“Background” level
Red line: Expected deaths each year
Cécile Viboud, et al. Emerg Infect Dis [serial on the Internet]. 2006 Apr. Available from
http://www.cdc.gov/ncidod/EID/vol12no04/05-0695-G2.htm
Epidemiology Terms
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Epidemic
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When the cases of a disease exceed what is normally
expected
Pandemic
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An epidemic that occurs over a large geographic area, or
across the whole world
Seasonal Epidemics vs. Pandemics
Seasonal Influenza
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A public health problem
each year
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Usually some immunity
built up from previous
exposures to the same
subtype
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Infants and elderly most
at risk
Influenza Pandemics
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Appear in the human
population rarely and
unpredictably
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Human population lacks
any immunity
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All age groups, including
healthy young adults
Seasonal Epidemics vs. Pandemics
Seasonal Influenza
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A public health problem
each year
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Usually some immunity
built up from previous
exposures to the same
subtype
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Infants and elderly most
at risk
Influenza Pandemics
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Appear in the human
population rarely and
unpredictably
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Human population lacks
any immunity
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All age groups, including
healthy young adults
Prerequisites for pandemic influenza
A new influenza virus emerges to which
the general population has little/no
immunity
The new virus must be able to replicate
in humans and cause disease
The new virus must be efficiently
transmitted from one human to another
Disease
Chain of Infection
+
Quantity of
pathogen
Virulence
Route of
transmission
Port
Sensitive
host
Avian Influenza precautions
Contact precautions
Droplet precautions
Airborne Precautions
Transmission of Influenza Viruses
Seasonal Influenza in Humans
Droplet
Yes
Airborne
Likely
Contact
Yes
Routes of Transmission
Droplet
Large droplets within 1 meter transmit
infection via:
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Coughing, sneezing, talking
Medical procedures
Routes of Transmission
Airborne (droplet nuclei)
Very small particles of evaporated
droplets or dust with infectious agent
may..
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Remain in air for a long time
Travel farther than droplets
Become aerosolized during procedures
General Information
Human
influenza
Vulnerable
Age Groups
Time from exposure
to illness
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All ages affected
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Highest rates in children < 5
years
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Most serious complications in
elderly >60 years
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Mean 2 days
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Range: 1 – 5 days
Signs and Symptoms
Human Influenza
Type of infection
Upper and lower respiratory
Fever
Yes
Headache
Yes
Cough
Yes
Respiratory symptoms
Gastrointestinal symptoms
Recovery
Varies; sore throat to difficulty
breathing
Uncommon, except children, elderly
2-7 days
Complications
Seasonal Influenza
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Ear infection, sinusitis
Bronchitis, bronchiolitis
Pneumonia
 viral or secondary bacterial
Exacerbation of chronic conditions
Muscle inflammation
Neurologic Disease
 Seizures
 Brain inflammation
 Reye’s syndrome
Prevention and
control
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Pharmaceutical interventions:
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Vaccination
Chemoprophylaxis
Non-pharmaceutical interventions NPI
Seasonal Vaccine
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Primary means of preventing influenza
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Proven efficacy / effectiveness to prevent infection, severe
illness (hospitalization) and death
Cost effective in many target groups, Safe,
Generally safe
350 million* doses produced annually (5% of
6.7 billion population)
Production and consumption highly localized.
 >95% produced in 9 countries (>65% in Europe)
 12% of population use 62% of vaccine
Production dependent on eggs
 Very little surge capacity
* 2006 estimate
Influenza Vaccine Benefits
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Can match a seasonal vaccine with a
circulating strain
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Can be highly effective for prevention of
seasonal influenza
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Vaccination of rapid responders reduces
the risk of infection and prevents viral
reassortment
Non-pharmaceutical Interventions
1. Delay disease transmission and outbreak peak
2. Decompress peak burden on healthcare infrastructure
3. Diminish overall cases and health impacts
#1
Pandemic outbreak:
No intervention
#2
Daily
Cases
Pandemic outbreak:
With intervention
#3
Days since First Case
Overview of NPI
Individual level
 Isolation
 Quarantine
 Infection control
Community level
 Quarantine of
groups/sites
 Measures to increase
social distance
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School closures
Business and market
closure
Cancellation of events
Movement restrictions
Infection control
Voluntary Isolation
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Separation and restricted movement of ill
persons with contagious disease (often in a
hospital setting and Primarily individual level)
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Isolate severe and mild cases
Location of isolation (home, hospital) depends on
several factors (severity of illness, the number of
affected persons, the domestic setting)
Do not wait for lab confirmation
Plan for large number of severe cases
Provide medical and social care
Voluntary Quarantine
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Separation and restricted movement of well
persons presumed exposed
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Identification of contacts
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Often at home, but may be designated
residential facility or hospital
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Applied at the individual or community level
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Regular health monitoring is essential part
of quarantine
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Self-health monitoring and reporting
Infection Control
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Hand hygiene
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Cough etiquette
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Facemasks
Hand Washing
Method
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Wet hands with clean (not hot) water
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Apply soap
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Rub hands together for at least 20 seconds
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Rinse with clean water
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Dry with disposable towel or air dry
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Use towel to turn off faucet
Alcohol-based Hand Rubs
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Effective if hands not visibly soiled
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More costly than soap & water
Method
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Apply appropriate (3ml) amount to
palms
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Rub hands together, covering all
surfaces until dry
Cough etiquette
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Respiratory
etiquette
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Cover nose / mouth when
coughing or sneezing
Hand washing!
Patients Cared for at Home
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Potential for transmission
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Must educate family caregivers
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Fever / symptom monitoring
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Infection control measures
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Hand washing
Use of available material as mask …
Treatment
Case Management
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Antivirals
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Consider age group
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Supportive care
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Antibiotics
Anti-viral Drugs: Classes of Influenza
Specific Antivirals
Neuraminidase inhibitors
1.
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Oseltamivir* (Tamiflu)
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Zanamivir (Relenza)
Adamantanes
2.
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Amantadine
Rimantadine
*Primary drug for mass chemoprophylaxis and for treating human
cases of avian influenza.
Neuraminidase Inhibitor
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Two drugs available
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Oseltamivir and zanamivir
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Should be given as soon as possible
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Effective for treatment and prevention
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Used for seasonal, avian and swine influenza
Oseltamivir Treatment in Seasonal
Influenza (5 days)
Adults:
75 mg twice a day for 5 days
Children:
<1 year, not studied adequately
< 15 kg - 30 mg twice a day
>15 kg to <23 kg - 45 mg twice a day
>23 kg to <40 kg - 60 mg twice a day
>40 kg - 75 mg twice a day
Zanamivir
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Inhaled by mouth via special device
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May be used for > 5 years of age
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Unstudied in human H5N1 illness
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Treatment dosage
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2 inhalations (10 mg), once in
morning and night for 5 days
Side effects
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Wheezing, and breathing problems