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ABCs of Influenza and Pandemics

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ABCs of Influenza and Pandemics Rapid Response Team Training in Southeast Asia Photo: Cynthia Goldsmith – PowerPoint PPT presentation

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Title: ABCs of Influenza and Pandemics


1
ABCs of Influenza and Pandemics

Rapid Response Team Training in Southeast Asia
Photo Cynthia Goldsmith
2
Learning Objectives
  • Describe the characteristics of influenza
    infection in humans
  • Understand different types of influenza viruses
    and how they can infect humans and animals
  • Describe the ways that influenza viruses can
    change or mutate

3
Learning Objectives
  • Describe the epidemiology of influenza and
    contrast pandemic influenza with seasonal
    influenza outbreaks
  • Understand the recent history of avian influenza
    outbreaks in humans
  • Describe the epidemiology and clinical
    characteristics of the H5N1 outbreak in humans

4
Session Overview
  • Influenza infection in humans
  • Influenza virus
  • Influenza epidemiology
  • Avian influenza infection in humans

5
Influenza Infection in Humans
6
Key Characteristics
  • Influenza is usually a respiratory infection
  • Transmission
  • Highly contagious
  • Primarily through contact with respiratory
    droplets
  • Transmission from objects possible

7
Key Characteristics
  • Communicability
  • Transmission 1 - 2 days before to 4 - 5 days
    after onset of symptoms (about 3 5 days of
    viral shedding)
  • Peak viral shedding occurs on day 1 of symptoms
  • Infants, children and the immunocompromised may
    shed the virus longer

8
Key Characteristics
  • Incubation period
  • Time from exposure to onset of symptoms
  • 1 to 5 days (average 2 days)
  • Seasonality
  • In temperate zones, sharp peaks in winter months
  • In tropical zones, circulates year-round with
    seasonal increases

9
Typical Signs and Symptoms
  • Rapid onset of symptoms
  • Fever / Chills
  • Body aches
  • Sore throat
  • Non-productive cough
  • Runny nose
  • Headache

10
Groups at Risk for Serious Complications
  • Complications
  • Pneumonia, worsening of chronic lung and heart
    problems, and death
  • High Risk Groups
  • Persons 65 years and older
  • Persons with chronic diseases
  • Infants between 6 months and 2 years
  • Pregnant women
  • Nursing home residents
  • Children on long-term aspirin therapy

11
Vaccination
  • Influenza vaccine is the best prevention for
    seasonal influenza.
  • Inactivated viruses in the vaccine developed from
    three circulating strains (generally 2 Type A and
    1 Type B strain)
  • Therefore, seasonal flu shot only works for 3
    influenza subtypes and will not work on pandemic
    strains.
  • In temperate zones, the vaccine is administered
    intramuscularly to all high risk persons gt 6
    months
  • Limited supply of intranasal vaccine is available

12
Influenza Virus
13
Influenza VirusTypes A and B
Type A Type B
Can cause significant disease Generally causes milder disease but may also cause severe disease
Infects humans and other species (e.g., birds) Limited to humans
Can cause epidemics and pandemics (worldwide epidemics) Generally causes milder epidemics
14
Influenza A Virus Subtyping
  • Influenza A subtypes are determined by two
    surface glycoproteins
  • Hemagglutinin (HA)
  • Neuraminidase (NA)
  • 16 HAs and 9 NAs

15
Species Infected by Influenza A, HA and NA
Subtypes
N1
H1
N2
H2
N3
H3
N4
H4
H5
N5
H6
N6
H7
N7
H8
N8
H9
N9
H10
H11
H12
H13
H14
H15,16
16
Surface Protein Changes
  • Antigenic DRIFT
  • Minor change in HA / NA
  • Point mutations during replication, but subtype
    remains the same
  • Continuous changes, so the virus avoids immunity
  • Limited partial immunity may exist to changed
    virus
  • Results in the need to update vaccines annually
  • Antigenic SHIFT
  • Major change in HA / NA
  • New subtype introduced
  • Caused by genetic re-assortment when 2 subtypes
    infect a host simultaneously
  • OR
  • Caused by direct transmission from birds or other
    animals to humans

17
Re-assortment and Direct Transmission
Non-human virus
Human virus
Reassortant virus
18
Influenza Epidemiology
19
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
20
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

21
Impact of Seasonal Influenza
  • An annual public health problem
  • Substantial health impact
  • 10 - 35 of children each year
  • 5 - 20 of adults each year
  • Substantial economic impact
  • Lost work / school days
  • Overwhelmed medical care systems
  • High incidence and costs in tropical zones (e.g.,
    Singapore, Hong Kong, Thailand)

22
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
  • Result of Antigenic Drift
  • Influenza Pandemics
  • Appear in the human population rarely and
    unpredictably
  • Human population lacks any immunity
  • All age groups, including healthy young adults,
    may be at increased risk for serious
    complications
  • Result of Antigenic Shift

23
Mortality Impact of Past Pandemics
  • 1918-19 Spanish Flu (H1N1)
  • 40 million deaths worldwide
  • 1957-58 Asian Flu (H2N2)
  • 1 - 2 million deaths worldwide
  • 1968-69 Hong Kong Flu (H3N2)
  • 700,000 deaths worldwide

24
Timeline of Influenza Pandemics
H9
Avian Influenza
H7
H5
H3
H2
H1
1915 1925 1935 1945 1955 1965
1975 1985 1995 2005
1918
Spanish Influenza H1N1
25
WHO Stages of a Pandemic
  • Inter-pandemic period
  • Pandemic alert period
  • Pandemic period
  • Post pandemic period

26
WHO Phases of a Pandemic
  • Inter-pandemic Period
  • Phase 1 No new Influenza virus subtypes in
    humans
  • Phase 2 No new virus subtypes in humans
    animal subtype poses a risk of human disease

27
WHO Phases of a Pandemic
  • Pandemic Alert Period
  • Phase 3 Human infection with novel virus no
    instances of human-to-human spread
  • Phase 4 Small, localized clusters of
    human-to-human spread
  • Phase 5 Larger clusters, still localized
    virus adapting to humans

28
WHO Phases of a Pandemic
  • Pandemic Period
  • Phase 6 Increased and sustained transmission
    in the general population.
  • Post Pandemic Period
  • Recovery phase

29
Avian Influenza
30
Avian Influenza
  • Type A influenza
  • Endemic in birds
  • H5, H7 subtypes can cause serious disease or
    death in wild birds often cause death in poultry
  • Virus in saliva and feces of wild birds and
    poultry can be directly transmitted to humans and
    other animals
  • Can contaminate clothing, equipment, water, feed

31
Avian Influenza
  • Low pathogenic AI (LPAI)
  • Most common influenza infection in birds
  • Causes mild clinical and unapparent infections
  • May be any subtype (H1 to H15)
  • Highly pathogenic AI (HPAI)
  • Some H5 or H7 subtypes
  • Causes severe illness in poultry and often death
  • LPAI H5 or H7 subtypes can mutate into HPAI H5
    or H7 subtypes

32
Avian Influenza in Humans
Year Subtype Location Cases Deaths
1996 H7N7 United Kingdom 1 0
1997 H5N1 Hong Kong 18 6
1998 H9N2 China 6 0
1999 H9N2 Hong Kong 2 0
2002 H7N2 United States 1 0
2003 H7N2 United States 1 0
2003 H9N2 Hong Kong 1 0
2003 H5N1 Hong Kong 2 1
2003 H7N7 The Netherlands 89 1
2004 H7N3 Canada 2 0
2003-06 H5N1 Worldwide 228 130
33
H5N1 Clinical Features
  • Incubation period likely 2 - 8 days but may be
    longer
  • Initial symptoms
  • High fever (gt38 C)
  • Respiratory symptoms (e.g., cough, sore throat,
    runny nose)
  • Muscle aches, headache
  • More rare frequent watery diarrhea, abdominal
    pain, vomiting

Source The Writing Committee of the World
Health Organization (WHO) Consultation on Human
Influenza A/H5. Avian Influenza A (H5N1)
infection in humans. N Engl J Med. 2005 Sep
29353(13)1374-85.
34
H5N1 Clinical Features
  • Clinical course
  • Shortness of breath (Dyspnea)
  • Clinical pneumonia with variable x-ray findings
  • Acute Respiratory Distress Syndrome (ARDS)
  • Case Fatality Rate (53)

Source The Writing Committee of the World
Health Organization (WHO) Consultation on Human
Influenza A/H5. Avian Influenza A (H5N1)
infection in humans. N Engl J Med. 2005 Sep
29353(13)1374-85.
35
Worldwide H5N1 Outbreak in Humans 2003 - 2006
Source WHO
36
H5N1 Possible Travel Routes
  • Legal poultry business
  • Illegal bird trade
  • Untreated fertilizer
  • Migrating birds
  • Humans (contaminated objects, intentional spread)

37
H5N1 in Other Animals
  • H5N1 can infect other animals
  • Pigs (China, Vietnam)
  • Domestic cats has infected civet cats
  • Tigers, leopards (Thailand, China)
  • Tiger-to-tiger transmission (Thailand)

38
Human H5N1 Epidemiology, Western Pacific Region
  • In contrast to seasonal influenza, most H5N1
    cases occur in previously healthy children and
    young adults.

Source WHO Regional Office for the
Western Pacific
39
Human H5N1 Epidemiology
  • Primarily avian-to-human transmission
  • No evidence of sustained person-to-person spread
  • Limited probable person-to-person spread1
  • Environment-to-human transmission possible

1 N Engl J Med 2005352333-340
40
Influenza Pandemic Requirements
  • A new Influenza subtype can infect humans
  • AND
  • This new virus causes serious illness in humans
  • AND
  • The new virus spreads easily from
    person-to-person

41
Summary
  • Influenza is a serious human and veterinary
    health concern each year
  • Influenza virus strains evolve rapidly and can
    develop into a novel virus with pandemic
    potential
  • Influenza pandemics have caused high morbidity
    and mortality in the past

42
Summary
  • H5N1 Avian Influenza is currently spreading
    through birds with occasional outbreaks among
    humans
  • While there is evidence of rare human to human
    transmission, sustained transmission has not
    occurred
  • If H5N1 virus obtains the ability to easily
    transmit from person to person, a pandemic may
    result

43
Questions?
44
Glossary
  • Virus
  • A small, infectious agent consisting of a core of
    genetic material (DNA or RNA) surrounded by a
    shell of protein. A virus needs a living cell a
    host to reproduce.
  • Viral shedding
  • Multiplication of a virus in an infected person
    with subsequent release of the virus from that
    infected person, such that others who come into
    contact with the person may become infected. A
    state of being contagious.
  • Epidemiology
  • The branch of medicine that deals with the study
    of the causes, distribution, and control of
    disease in populations.

45
Glossary
  • Seasonal Influenza
  • Expected rise in influenza occurrence among
    humans living in temperate climates occurs
    during the winter season with strains of
    influenza that have minor changes from season to
    season.
  • Pandemic
  • An epidemic occurring over a wide geographic area
    and affecting a large proportion of the
    population.
  • Antigenic Drift
  • A process of small changes in the genetic
    material of a virus, called point mutations, that
    occur during the normal virus replication
    process.

46
Glossary
  • Antigenic Shift
  • A process of major changes in the genetic
    material of a virus for influenza, the H and N
    proteins change altogether, resulting in a new
    strain of virus.
  • Highly Pathogenic Avian Influenza (HPAI)
  • Influenza infection in poultry that causes severe
    illness and often death. Can be transmitted to
    humans resulting in severe illness or death.
  • Low Pathogenic Avian Influenza (LPAI)
  • The most common influenza infection in birds
    causes mild clinical and unapparent infections.

47
References and Resources
  • 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
  • The Writing Committee of the World Health
    Organization (WHO) Consultation on Human
    Influenza A/H5. Avian Influenza A (H5N1)
    infection in humans. N Engl J Med. 2005 Sep
    29353(13)1374-85.
  • Ungchusak K, et al. Probable Person-to-Person
    Transmission of Avian Influenza A (H5N1) N Engl
    J Med 2005352333-340.

48
References and Resources
  • Tiensin T, et al. Highly Pathogenic Avian
    Influenza H5N1, Thailand, 2004.
    EID200511(11)1664-72. http//www.cdc.gov/ncidod
    /eid/vol11no11/05-0608.htm
  • World Health Organization. Epidemic and Pandemic
    Alert and Response. 2006. http//www.who.int/csr/e
    n/
  • Center for Food Security and Public Health. Iowa
    State University http//www.cfsph.iastate.edu/
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