Influenza: virus, disease, prevention

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Influenzavirus, disease, prevention control,
treatment
Lecture presented byDr Ghassan Awar02 May 2009
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Virus
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Influenza Virus
Orthomyxovirus
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The Virus
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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

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Influenza VirusTypes A and B
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Influenza A Virus Subtyping

• Influenza A subtypes are determined by two
  surface glycoproteins
• Hemagglutinin (HA)
• Neuraminidase (NA)
• 16 HAs and 9 NAs

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Species Infected by Influenza A, HA and NA
Subtypes
N1
H1
N2
H2
N3
H3
H4
N4
H5
N5
H6
N6
H7
N7
H8
N8
H9
N9
H10
H11
H12
H13
H14
H15,16
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Influenza Nomenclature
Influenza type
Hemagglutinin subtype
Year of isolation
A/Sydney/5/97 (H3N2)
Geographic source
Isolate number
Neuraminidase subtype
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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)

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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

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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

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Examples of Re-assortment and Direct Transmission
Non-human virus
Human virus
RE-ASSORTMENT
Reassortant virus
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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
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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

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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

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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

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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
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Disease
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Chain of Infection

Sensitive host
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Avian Influenza precautions
Contact precautions
Droplet precautions
Airborne Precautions
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Transmission of Influenza Viruses
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Routes of TransmissionDroplet

• Large droplets within 1 meter transmit
• infection via
• Coughing, sneezing, talking
• Medical procedures

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Routes of TransmissionAirborne (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

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General Information
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Signs and Symptoms
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Complications

• Seasonal Influenza
• Ear infection, sinusitis
• Bronchitis, bronchiolitis
• Pneumonia
• viral or secondary bacterial
• Exacerbation of chronic conditions
• Muscle inflammation
• Neurologic Disease
• Seizures
• Brain inflammation
• Reyes syndrome

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Prevention and control
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• Pharmaceutical interventions
• Vaccination
• Chemoprophylaxis
• Non-pharmaceutical interventions NPI

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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.
• gt95 produced in 9 countries (gt65 in Europe)
• 12 of population use 62 of vaccine
• Production dependent on eggs
• Very little surge capacity
• 2006 estimate

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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

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Non-pharmaceutical Interventions
1. Delay disease transmission and outbreak
peak 2. Decompress peak burden on healthcare
infrastructure 3. Diminish overall cases and
health impacts
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Overview of NPI

• Community level
• Quarantine of groups/sites
• Measures to increase social distance
• School closures
• Business and market closure
• Cancellation of events
• Movement restrictions
• Infection control

• Individual level
• Isolation
• Quarantine
• Infection control

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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

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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

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Infection Control

• Hand hygiene
• Cough etiquette
• Facemasks

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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

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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

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Cough etiquette

• Respiratory etiquette
• Cover nose / mouth when coughing or sneezing
• Hand washing!

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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

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Treatment
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Case Management

• Antivirals
• Consider age group
• Supportive care
• Antibiotics

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Anti-viral Drugs Classes of Influenza Specific
Antivirals

• Neuraminidase inhibitors
• Oseltamivir (Tamiflu)
• Zanamivir (Relenza)
• Adamantanes
• Amantadine
• Rimantadine

Primary drug for mass chemoprophylaxis and for
treating human cases of avian influenza.
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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

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Oseltamivir Treatment in Seasonal Influenza (5
days)

• Adults
• 75 mg twice a day for 5 days
• Children
• lt1 year, not studied adequately
• lt 15 kg - 30 mg twice a day
• gt15 kg to lt23 kg - 45 mg twice a day
• gt23 kg to lt40 kg - 60 mg twice a day
• gt40 kg - 75 mg twice a day

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Zanamivir

• Inhaled by mouth via special device
• May be used for gt 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