Download What’s up with the flu? - Winona Senior High School

What year do you
think this cover
was published?
1. What is the difference between
swine flu and avian flu?
2. Why is the flu always changing?
3. What makes a flu deadly?
4. Why are we so worried?
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Characteristics
- Nucleic acid surrounded by protein
- Can contain DNA or RNA as genetic material
- Can’t reproduce on their own, must employ a
cell to work for them
- Infects host cell by inserting its RNA or DNA
- Forces host cell to replicate genetic material
and proteins to make more viruses, killing the
cell
Surface
Proteins
Hemagglutinin (H)
Binds to receptors on
host cell surfaces,
“tricking” those cells
into taking the virus
inside
Neuraminidase (N)
Helps newly-formed
virus particles leave
the host cell
Viral genome
10 genes carried on
8 separate strands
of RNA.
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Flu strains evolve different forms of
Hemagglutinin & Neuraminidase.
These forms of H (16 known)and N(9
known) are assigned numbers (H1-H16;
N1-N9) used in naming flu strains.
“Avian(bird) flu” = H5N1
(evolved in Asia between 1999 and 2002)
2009 “swine flu” = H1N1
(probably originated in Mexico in 2008)
Turn to your neighbor and
explain to them how viruses
work and the difference
between swine flu and avian
flu.
ZOONOSIS:
A disease which is naturally transmissible from
animals to humans.
Flu strain 1
Flu strain 2
Two viral strains infect
the same host cell at the
same time
Host Cell
Flu strain 1
Flu strain 2
Host Cell
RNA from both strains is injected
into the host cell and replicated
As new viral particles are assembled,
RNA strands from the two strains can
sort independently, forming new
combinations of genes
Some newly-formed viruses that leave
the host cell carry new combinations of
genes from both parent strains
A strain of the flu could also spontaneously
mutate due to an error in the replication
machinery of the cell.
1.
2.
Transmissibility: How easily a strain
is transmitted from person to
person.
Immunogenicity: How rapidly a
viral strain can be recognized by
human immune systems. (this
depends on whether humans have
been exposed to it in the past)
1.
2.
3.
Viruses display an antigen protein.
A human antibody binds the antigen.
The virus can’t invade a cell
Has been infected before or vaccinated
Never encountered the virus before
Strains of Swine H1N1 that we know
about so far have:


Low virulence - they rarely cause serious illness
and are rarely lethal, but ...
High human-to-human transmissibility - they
spread easily from person to person.
Strains of Avian H5N1 we know
about so far have:


High virulence -they cause serious illness and
can be lethal) ... but ...
Low human-to-human transmissibility - they do
not spread easily from person to person.



On average 36,000 people die from the flu
every year in the United States, 90% are over 65
Swine flu has killed more than 1,000 people,
but it is not more deadly than the seasonal flu
As of October 2005, only 116 confirmed cases of
the H5N1 strain of flu being transmitted from
infected birds to people. But 60 of those people
have died -- a death rate greater than 50
percent, making it one of the most virulent
strains ever seen
Are either avian flu or swine flu
likely to cause a pandemic?
p.s. What does pandemic mean?
Pan = everything
Demic = people
Right now, the avian flu is
reproductively isolated in birds. It
does not spread easily to humans or
from human to human. However, if the
avian flu were to mutate or recombine
with a human flu strain, this highly
virulent flu strain could also become
highly transmissible.
Turn to your neighbor…what did I just say?

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Spontaneous Mutations
Recombination between two flu strains.
Vaccinations (if the majority of a human
population is vaccinated, the flu has a harder
time spreading)
Human and animal immune systems (have we
seen this flu before? Is our system ready for it?)
Human and animal interactions (farming
practices, travel, war)
“Human social ecology” includes population density, where we live, the way
we travel, and the way we produce our food.
Changes in any of these factors can alter interactions among human
populations, domestic animal populations, and wild animal populations.
These interactions, in turn, affect the way pathogens evolve, get transmitted,
and make us sick.
(From “The Social Ecology of Infectious Disease” by Kenneth H. Mayer and
H.F. Pizer)
….so we drive the evolution of the flu.
Be careful.