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Adenovirus - cause of the common cold
Viruses
Viruses are insidious pathogens, they attack cells from the
inside. They hijack your own DNA and use it against
you. A virus cannot be treated with antibiotics, it can only
run its course until your immune system kicks it out.
..Even then, the virus may lay dormant within the cells and
come back at a later date
Properties of viruses
no membranes, cytoplasm, ribosomes, or other cellular
components
they cannot move or grow
they can only reproduce inside a host cell
they consist of 2 major parts - a protein coat, and hereditary
material (DNA or RNA)
they are extremely tiny, much smaller than a cell and only
visible with advanced electron microscopes
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Virus Structure
What Is a Virus?
T4 Bacteriophage
Tobacco Mosaic Virus
Influenza Virus
RNA
Head
DNA
RNA
Capsid
Tail
sheath
Tail fiber
Membrane
envelope
Capsid
proteins
Surface
proteins
Parasitic Nature
Obligate intracellular parasites (they cannot exist independently)
Specific to hosts (human, dog, some can cross species)
Specific to cells , the common cold is a virus that specifically
attacks cells of the respiratory track (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.
See
animation http://www.youtube.com/watch?v=41aqxcxsX2w&feature=relat
ed
Viral Reproduction
Lytic cycle = reproduction occurs, cells burst
Lysogenic cycle = reproduction does not immediately occur
(dormancy)
Virulent = viruses that undergo both cycles
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.
1. Attachment
2. Penetration - the virus is engulfed by the cell
(Cell can enter Lysogenic or Lytic Cycle)
3. Biosynthesis - viral components are made
(protein coat, capsid, DNA/RNA)
4. Maturation - assembly of viral components
5. Release - viruses leave host cell to infect new cells
(often destroys host)
Retroviruses -- RNA viruses that have a DNA stage
• Human Immunodefiency Virus - causes AIDS
• Retrovirus (RNA inside a protein coat)
• Reverse Transcriptase makes DNA from the virus RNA
• DNA inserts into host DNA
• Proteins are assembled from the DNA code
• Viruses assembled from the proteins
• Viruses released from the cell
(Link) HIV Animation - how virus infects cells
HIV/AIDS
Human Immunodeficiency Virus/ Acquired
Immunodeficiency Syndrome
By damaging your immune system, HIV interferes
with your body's ability to fight off viruses, bacteria
and fungi that cause disease.
It is a blood born pathogen and passed from person
to person and possibly animal to human.
makes you more susceptible to certain types of
cancers and to infections your body would normally
resist, such as pneumonia and meningitis.
An estimated 39.5 million people have HIV
worldwide
What we know about HIV.....
Developing a vaccine for AIDS is difficult because it is a
RETROVIRUS. RNA mutates easily and each individual virus can be
slightly different from the others. In fact, different viruses can exist
within the same person.
See: HIV coloring
Emerging Viruses
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 (avian flu, swine flu)
West Nile Virus
Transmitted by mosquitoes
One may only experience minor symptoms such as
a skin rash and headache.
Some develop a life-threatening illness that
includes inflammation of the brain
It first appeared in the United States in the summer of
1999 and since then has been found in all 48 contiguous
states.
How would you protect yourself?
SARS Virus
Usually, changes in viral antigens are small. The
illness these “antigenic drift” variants produce is
annoying, but not usually life-threatening.
But now and then a major change in antigens occurs.
These “antigenic shifts” can produce devastating results
-- lethal, global epidemics.
The most serious occurred during World War I; It killed
675,00 Americans and between 20 and 50 million
people worldwide. That’s more than all the wars of the
20th century put together.
Swine flu of 1918 Swine flu trailer
A billion people (1/2 the worlds population at the time) were infected with
the flu; 40-50 million died. One year later, the pandemic was over. It
was considered the deadliest pandemic in history. What caused it?...
Frozen bodies in Alaska permafrost (from 1918) were autopsied and
preserved lung tissue (in wax) were tested. Evidence suggests that the
virus’ ancestor may have been an avian flu virus; one well-adapted to
humans.
What we know about the 1918 flu:
The 1918 flu virus appears to have jumped, directly, from birds to
humans.
That jump, high virulence, and human-human transmissibility appear to
be dependent on a small number of changes in the flu genome.
Certain evolving strains of the current H5N1 avian flu strains have
accumulated 5 of an estimated 10 mutations related to human-human
infectivity.
There are actually three parallel routes, any
or all of which could transform the current
situation into a deadly pandemic.
Why are some flu strains just a nuisance, while
others are dangerous?
Our immune system identifies and attacks pathogens
it recognizes. What if the hemogglutinin site of the
virus is not known?
Antibodies can’t bind!
Bird migration can spread a bird virus around the
world! People travel, too.
What’s the problem?
Swine flu is really a bird flu that’s
changed…and keeps changing.
The virus can evolve in other
animals, so your body can’t
recognize it. It can make you very
sick or kill you…jut like regular
human Influenza A.
How do you protect yourself?
•Wash your hands often.
•Stay away from sick people.
•Keep your immune system strong
by eating healthy, sleeping enough,
and exercising.
•Get a flu shot if you are in a high
risk group.
•Stay away from well people, when
you are sick. Get medical attention.
H1N1 Swine Flu
How Do Vaccines Work?
1. Once you have gotten a virus, such as chicken pox, your body
develops the immunity to that virus.
2. Vaccines are made by growing a weakened or killed form of the
virus (often grown in eggs)
3. This form of the virus is injected into a person's body, which causes
an immune response, and immunity to the virus.
- Remember Jenner's
cowpox vaccine?
RV = rotovirus; DTaP = diptheria, tetanus, pertussis (whooping cough); Hib =
haemophilus influenza type B; PCV = pneumococcal vaccine; IPV = inactivated
polio virus; MMR = measles, mumps, rubella,
Some parents are
opting out of
immunizations due to
fears about vaccine
safety.
In response,
government agencies
are producing
commercials to
encourage parents to
get their child
vaccinated.
Discuss:
1. What are the risks of vaccines? Are they safe?
2. Would you have your own child vaccinated?
3. Should the government force immunizations?
INFLUENZA
BACTERIOPHAGE
H1N1
SMALLPOX
How big are viruses?
Related to Viruses
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, also may cause Kuru in cannibal tribes
See:
http://highered.mcgraw-hill.com/sites/007352543x/student_view0/chapter20/how_prions_arise.html