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Introduction to Influenza


INTRODUCTION TO INFLUENZA The (Ferret) Sneeze Heard Around The World: The Case Of The Bioengineered Bird Flu Case Study for AAC&U STIRS Project – PowerPoint PPT presentation

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Title: Introduction to Influenza

Introduction to Influenza
  • The (Ferret) Sneeze Heard Around The World The
    Case Of The Bioengineered Bird Flu
  • Case Study for AACU STIRS Project
  • Jill M. Manske
  • University of St. Thomas

Introduction to Influenza
From Bird Flu A Virus of our own
Hatching http//
(No Transcript)
  • Has an RNA genome (8 genes)
  • Highly variable virus
  • Lipid envelope with protein spikes
  • Relatively unstable at room temperature (half
    life a few hours)
  • There is a species barrier due mostly structure
    of HA protein

What are the H and the N of Influenza Viruses?
  • HEMAGGLUTININ (HA) - The H in influenza names
  • On the surface of the virus
  • Functions as the receptor for the virus to bind
    to the host cell
  • There are 17 different subtypes of HA
    (representing the numbers, H1, H5, etc. in
    influenza naming)
  • HA elicits an immune response and is part of the
    influenza vaccine
  • NEURAMINIDASE (NA) - The N in influenza names
  • On the surface of the virus
  • Functions as an enzyme to let the new viral
    particles out of the host cell
  • There are 10 different NA subtypes
  • NA is also part of the influenza vaccine

Important Note
  • The species which different types of influenza
    viruses are able to infect are determined by HA
    receptor binding to different forms of the
    receptor present on the host cell
  • This provides a considerable species barrier
    between birds and humans which is not easily
  • Pigs provide a "mixing pot" - able to be infected
    by both types of virus thus allowing the
    passage of avian viruses to humans.

Types, Subtypes, Strains
  • Types Based on structure of internal proteins
  • Type A infects humans, birds, pigs, horses,
    other animals. Wild birds are natural hosts
  • Further Classified by Subtype (based on HA and NA
    proteins) and strains based on antigenic drift
    (more later)
  • Pandemics are associated with Type A
  • Type B Usually found in humans
  • Classified by strain only
  • Not associated with Pandemics
  • Type C Human infections rare

Classification(naming) of influenza strains
  • Type A, B or C/place isolated/number of
    isolate/year isolated
  • In the case of influenza A, also HA subtype (H)
    and NA subtype (N)
  • For example, the three strains for the 2013/2014
    vaccine are
  • A/California/7/2009 (H1N1)pdm09-like virus
  • A/Texas/50/2012 (H3N2)
  • B/Massachusetts/2/2012-like virus
  • Quadravalent vaccine has additional

Examples of different subtypes and the species
they infect
How the Flu Virus Changes Antigenic shift and
Flu viruses constantly change and
mutate. Antigenic drift refers to changes to the
flu virus that happen slowly over time.
Antigenic shift results when two different flu
strains combine and infect the same cell and
their genomes combine. This results in a sudden
change in the virus. This can result in a
pandemic strain.
CDC How influenza viruses change
More information can be found at
Example Viral Reassortment of the 2009 H1N1
Pandemic Influenza Virus
A(H1N1)pdm09 Triple reassortment 7 genes from
avian and swine 1 gene from human H3N2
Spread Of The Virus
  • Person to person via particle aerosols that can
    get into respiratory tract.
  • - Can spread up to about 6 feet away
  • Infectious about 1 day before symptoms and 5-7
    days after symptoms.
  • - May be longer than 7 days in children
  • The incubation period is short ? - symptoms
    appear 1 4 days after infection
  • Viral titers (amounts) are usually high so there
    are enough infectious virions in a small droplet
    to start a new infection.

Seasonal Influenza
  • Seasonal influenza follows a predictable season
  • Most people have some immunity due to previous
    exposure to influenza viruses
  • Seasonal influenza viruses change slightly
    through antigenic shift
  • Ahead of each influenza season we develop a
  • WHO estimates that worldwide seasonal epidemics
    result in 3-5 million cases of severe illness and
    250,000-500,000 deaths every year

Pandemic Influenza
  • Human influenza pandemics are a part of our
  • 11 in the past 300 years
  • Novel influenza virus subtype emerges in humans
  • little or no human immunity
  • transmission of the virus to humans by humans
  • moderate to severe disease occurrence

What Happens After You Inhale Influenza Virus?
  • After influenza viruses are inhaled, HA spikes on
    their surfaces bind to molecules on the surface
    of cells lining the respiratory tract.
  • Then the viruses are engulfed into the cell.
  • The viral components are released into the cell
  • The virus replicates its viral RNA and makes
    viral proteins.
  • Newly formed viral particles migrate through the
    cell and begin to bud through the cell membrane
  • The NA molecules on the surface of the new
    viruses allow them to exit from the host cell
  • The newly formed viruses are released and find
    new cells to invade.

What happened here?
An estimated 20-40 million people died during
the1918-1919 Influenza Pandemic.
Learn more about the 1918 and other influenza
The Bird Flu H5N1 Avian Influenza
The Bird Flu H5N1 Avian Influenza
  • Highly Pathogenic avian influenza (HPAI) H5N1
    infection is rare in humans
  • More than 600 cases have been reported since
  • Infection can lead to severe disease. Of the
    reported cases, 60 of infected people died.
  • Most Cases of H5N1 in people have been linked to
    contact with infected poultry
  • In the majority of cases, the person got HPAI
    H5N1 virus infection after direct or close
    contact with sick or dead infected poultry.

Source CDC- Highly Pathogenic Avian Influenza in
People. More information
H1N1 vs H5N1 infection in humans
622 cases 371 deaths
VaccinesHow to make flu vaccine?
  • Choose virus inject into fertilized egg
  • Incubate egg and allow for viral replication
  • Collect allantoic fluid from the egg - full of
    live virus
  • Deactivate and chop virus-- mix with other
    strains for seasonal vaccine

In the past few decades
  • 1973- WHO begins to recommend composition of
  • 1999- 2 sets of recommendations
  • Southern and Northern hemispheres

Todays Vaccine Options
  • 2013-14 Northern Hemisphere composition
  • Trivalent
  • A/California/7/2009 (H1N1)pdm09-like virus
  • A(H3N2) virus (A/Texas/50/2012)
  • B/Massachusetts/2/2012-like virus
  • Quadrivalent
  • Above three..
  • B/Brisbane/60/2008-like virus
  • Vaccines containing cell-cultured virus