Transcript Slide 1
Influenza:
virus, disease, prevention
& control, treatment
Lecture presented by
Dr Ghassan Awar
02 May 2009
Virus
Influenza Virus
Orthomyxovirus
3
The Virus
Types of Influenza Virus
Three types: A, B, C
Influenza Type A can infect: People, birds, pigs,
horses, seals, whales and others
Influenza Type B: Human virus
Not classified according to Subtype
Cause human epidemics but not pandemics
Influenza Type C cause mild illness in humans
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
•
Influenza A subtypes are determined by two
surface glycoproteins:
Hemagglutinin (HA)
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
Point mutations in the hemagglutinin gene cause
minor antigenic changes to HA
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:
6-8 months process
Targeted at high-risk (inactivated)
Antigenic Shift
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?
Antigenic Shift
Strong selection pressure acting on
mutations or changes in HA or NA
Direct infection in humans
Re-assortment
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
Endemic
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
Epidemic
When the cases of a disease exceed what is normally
expected
Pandemic
An epidemic that occurs over a large geographic area, or
across the whole world
Seasonal Epidemics vs. Pandemics
Seasonal Influenza
A public health problem
each year
Usually some immunity
built up from previous
exposures to the same
subtype
Infants and elderly most
at risk
Influenza Pandemics
Appear in the human
population rarely and
unpredictably
Human population lacks
any immunity
All age groups, including
healthy young adults
Seasonal Epidemics vs. Pandemics
Seasonal Influenza
A public health problem
each year
Usually some immunity
built up from previous
exposures to the same
subtype
Infants and elderly most
at risk
Influenza Pandemics
Appear in the human
population rarely and
unpredictably
Human population lacks
any immunity
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:
Coughing, sneezing, talking
Medical procedures
Routes of Transmission
Airborne (droplet nuclei)
Very small particles of evaporated
droplets or dust with infectious agent
may..
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
All ages affected
Highest rates in children < 5
years
Most serious complications in
elderly >60 years
Mean 2 days
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
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
Pharmaceutical interventions:
Vaccination
Chemoprophylaxis
Non-pharmaceutical interventions NPI
Seasonal Vaccine
Primary means of preventing influenza
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
Can match a seasonal vaccine with a
circulating strain
Can be highly effective for prevention of
seasonal influenza
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
School closures
Business and market
closure
Cancellation of events
Movement restrictions
Infection control
Voluntary Isolation
Separation and restricted movement of ill
persons with contagious disease (often in a
hospital setting and Primarily individual level)
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
Separation and restricted movement of well
persons presumed exposed
Identification of contacts
Often at home, but may be designated
residential facility or hospital
Applied at the individual or community level
Regular health monitoring is essential part
of quarantine
Self-health monitoring and reporting
Infection Control
Hand hygiene
Cough etiquette
Facemasks
Hand Washing
Method
Wet hands with clean (not hot) water
Apply soap
Rub hands together for at least 20 seconds
Rinse with clean water
Dry with disposable towel or air dry
Use towel to turn off faucet
Alcohol-based Hand Rubs
Effective if hands not visibly soiled
More costly than soap & water
Method
Apply appropriate (3ml) amount to
palms
Rub hands together, covering all
surfaces until dry
Cough etiquette
Respiratory
etiquette
Cover nose / mouth when
coughing or sneezing
Hand washing!
Patients Cared for at Home
Potential for transmission
Must educate family caregivers
Fever / symptom monitoring
Infection control measures
Hand washing
Use of available material as mask …
Treatment
Case Management
Antivirals
Consider age group
Supportive care
Antibiotics
Anti-viral Drugs: Classes of Influenza
Specific Antivirals
Neuraminidase inhibitors
1.
Oseltamivir* (Tamiflu)
Zanamivir (Relenza)
Adamantanes
2.
Amantadine
Rimantadine
*Primary drug for mass chemoprophylaxis and for treating human
cases of avian influenza.
Neuraminidase Inhibitor
Two drugs available
Oseltamivir and zanamivir
Should be given as soon as possible
Effective for treatment and prevention
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
Inhaled by mouth via special device
May be used for > 5 years of age
Unstudied in human H5N1 illness
Treatment dosage
2 inhalations (10 mg), once in
morning and night for 5 days
Side effects
Wheezing, and breathing problems