Transcript Adenovirus - cause of the common cold 19-3 Viruses     A virus is a particle of nucleic acid, protein, and sometimes lipids, that can reproduce.

Adenovirus - cause of the common cold
19-3 Viruses
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A virus is a particle of nucleic
acid, protein, and sometimes
lipids, that can reproduce only
by infecting living cells –
viruses DO NOT have all the
characteristics of life and are
not considered to be organisms
Viruses are insidious pathogens
that attack cells form the
inside, hijack the DNA and use
it against the host
A virus cannot be treated with
antibiotics and can only run its
course until the immune
system kicks it out (if it can)…
…and even then, it may just be
laying dormant to return at a
later date
The Common
Cold – What is it?
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The common cold is a group of symptoms in the upper
respiratory tract caused by a large number of different
viruses
Although more than 200 viruses can cause the common
cold, the perpetrator is usually the rhinovirus, which is to
blame for causing 10% to 40% of colds
Also, the coronaviruses cause about 20% of colds
Corona Virus
What is the flu?
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Influenza (the flu) is a contagious respiratory illness
caused by influenza viruses
It can cause mild to severe illness, and at times can lead
to death
Each year in the United States on average, 5% to 20%
of the population gets the flu; on average, more than
200,000 people are hospitalized from flu-related
complications, and about 36,000 people die from flurelated causes
There are many different types of flu virus, or “strains”
that circulate from year to year and make people sick
Properties of
Viruses
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No membranes, cytoplasm, ribosomes, or other cellular
components
They cannot move, grow, or use energy
They can only reproduce inside a host cell
They consist of 2 major parts – a protein coat (capsid),
and a core of hereditary material (DNA or RNA)
They are extremely tiny, much smaller than a cell, and
only visible with advanced electron microscopes
Grouped by type of organism they infect (animal, plant,
bacteria)
Virus Structure
Virus Types
Parasitic Nature
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Obligate intracellular
parasites – are only active
inside a host cell & then only
reproduce more viruses
Specific to their hosts
(human, dog, bacteria, etc.
– some can cross species
EX. Flu virus)
They can only attack specific
cells – the common cold is a
virus that specifically attacks
cells of the respiratory tract
(hence the coughing and
sneezing and sniffling), HIV
specifically attacks white
blood cells
This is a bacteriophage, a type of
virus that attacks bacteria. It is
recognizeable because it looks like
the lunar landing spaceship.
Viral Reproduction (Lytic Cycle
and/or Lysogenic Cycle)
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Lytic Cycle – Viral reproduction occurs, cells
burst
Lysogenic Cycle – Viral reproduction does not
occur immediately (dormancy), viral DNA
becomes part of host DNA (prophage) – not all
viruses have a lysogenic cycle
Viruses that undergo both cycles are described
as virulent
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Viruses multiply, or replicate using their
own genetic material and the host cell's
machinery to create more viruses.
Viruses cannot reproduce on their own,
and must infect a host cell in order to
create more viruses.
Typical Sequence of Virus Reproduction:
1. Attachment
2. Penetration – the virus injects its genetic material or is
engulfed by the cell (virus enters lysogenic or lytic
cycle)
3. Biosynthesis – viral components are made (capsid,
enzymes, DNA/RNA)
4. Maturation – assembly of viral components
5. Release – viruses leave host cell to infect new cells
(immediately or eventually destroys host cell)
Virus Life Cycle - General
See: http://highered.mcgraw-hill.com/sites/007352543x/student_view0/chapter20/lambda_phage_replication_cycle.html
Retroviruses – RNA
viruses that have a
DNA stage
EX. Human Immunodeficiency Virus – causes AIDS
 Retrovirus (RNA inside a protein coat)
 Reverse transcriptase makes DNA from the virus RNA
 DNA inserts into host DNA (prophage)
 Proteins are assembled from the DNA code (protein
synthesis)
 Viruses are assembled from the proteins
 Viruses are released from the cell
HIV (Human Immunodeficiency Virus)
HIV Life Cycle Video
Emerging
Viruses
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Illnesses not previously known – AIDS, West Nile Virus,
SARS, Ebola, Bird Flu
Could be mutations of known viruses
Could be viruses exposed when new areas were
developed
Could have jumped species
What is “swine” or “H1N1” flu?
Swine flu is a new strain of the flu virus
that was first identified passing from
human to human in 2009
 Because this particular virus had never
circulated in human populations before,
few had natural immunity
 Many more people than were infected
with this particular strain of the virus,
although it did not turn out to be a
particularly virulent strain
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Percentage of Visits for Influenza-like Illness (ILI) Reported by
the U.S. Outpatient Influenza-like Illness Surveillance Network
(ILINet), National Summary 2008-2009 and Previous Two
Seasons (Week ending 11-14-09)
Swine Flu Virus
Swine Flu Virus
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Blue and Red
“spikes” represent
surface proteins
Blue are
hemagglutinin (HA)
proteins
Red are
neuraminidase (NA)
proteins
Flu Virus Names
There are 16 types of HA protein and 9
types of NA protein
 A flu virus has only one type of HA and
one type of NA, so that is how they are
named
 Swine flu is grouped as an “H1N1” virus
because it has type 1 HA protein and type
1 NA protein
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Related to Viruses
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Viroids – even smaller than viruses,
consist of RNA strands that lack a protein
coat
Prions – “rogue protein", believed to be
the cause of Mad Cow Disease
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http://highered.mcgrawhill.com/sites/007352543x/student_view0/chapter20/how_prions_arise.html
How do vaccines
work?
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Once you have gotten a virus, such as chicken pox,
your body develops the immunity to that virus
1. Vaccines are made by growing a weakened or killed form of
the virus (often grown in eggs)
2. This form of the virus is injected into a person's body, which
causes an immune response (T and B cell activation), and
immunity to that specific virus type
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It is difficult to develop vaccines for retroviruses (HIV,
influenza) because reverse transcriptase (RNA  DNA)
makes many random errors (mutations) which alters
the virus enough so that the immune system does not
recognize it
RV = rotovirus; DTaP = diptheria, tetanus, pertussis (whooping
cough); Hib = haemophilus influenza type B; PCV = pneumococcal
vaccine; IPV = inactivated polio virus; MMR = measles, mumps,
rubella,
Are vaccines safe?
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A vaccine, like any medicine, could cause serious
problems, such as a severe allergic reaction – but the
risk is extremely small
In most cases, the benefits of vaccination far
outweigh the potential risks
As a result of the vaccines discovered in the 20th
Century, parents and many healthcare providers of
the 21st Century have limited or no experience with
the devastating effects of diseases such as polio,
smallpox or measles. Fear of disease has shifted to
concerns regarding vaccine safety. Scientific evidence
has refuted many of the misconceptions regarding
vaccine safety; however, parental refusal of vaccines
is increasing.
Are vaccines
safe?
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The success of an immunization program depends on high rates
of acceptance and coverage.
 There is evidence of an increase in vaccine refusal in the
United States and of geographic clustering of refusals that
results in outbreaks.
 Children with exemptions from school immunization
requirements (a measure of vaccine refusal) are at increased
risk for measles and pertussis and can infect others who are
too young to be vaccinated, cannot be vaccinated for
medical reasons, or were vaccinated but did not have a
sufficient immunologic response.
Vaccine Success Story - Smallpox
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Smallpox is a highly
infectious, devastating, and
disfiguring disease that is
caused by variola virus
Smallpox is characterized by
numerous pustules
containing infectious virus
all over the body
The fatality rate is more
than one quarter of infected
patients infected by the
most serious form caused by
Variola major
Vaccine Success Story - Smallpox
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The disease killed an estimated 400,000 Europeans
each year during the 18th century
Of all those infected, 20–60% — and over 80% of
infected children — died from the disease
In the United States, from 1843 to 1855 first
Massachusetts, and then other states required
smallpox vaccination
By 1897, smallpox had largely been eliminated from
the United States
In the early 1950s an estimated 50 million cases of
smallpox occurred in the world each year
After successful vaccination campaigns throughout the
19th and 20th centuries, the WHO certified the
eradication of smallpox in December 1979
The last cases of smallpox in the world occurred in an
outbreak of two cases (one of which was fatal) in
Birmingham, England in 1978
Vaccine Success Story - Polio
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Polio is a viral disease, usually affecting
children and young adults, caused by any of
three polioviruses
Polio virus causes inflammation of the motor
neurons of the brain stem and spinal cord
Symptoms include motor paralysis, followed by
muscular atrophy and often permanent
deformities
Polio was one of the most dreaded childhood
diseases of the 20th century
Polio epidemics have crippled thousands of
people, mostly young children; the disease has
caused paralysis and death for much of human
history
Vaccine Success Story - Polio
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By 1910, much of the
world experienced a
dramatic increase in polio
cases and frequent
epidemics became
regular events, primarily
in cities during the
summer months
These epidemics left
thousands of children
and adults paralyzed
The polio vaccines developed by Jonas Salk in 1952 and
Albert Sabin in 1962 are credited with reducing the
global number of polio cases per year from many
hundreds of thousands to around a thousand
Links
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http://learn.genetics.utah.edu/content/be
gin/cells/scale/
http://www.xvivo.net/zirus-antivirotics/