Download Viruses - Mount Mansfield Union High School







Pathogens
 viruses that cause disease
Virulent
 disease causing
Latent
 inactive, but having the potential to be active at a later time
Antigen
 the protein of a virus, which is foreign to the invaded host
Temperate
 not immediately disease causing
 a temperate virus introduces nucleic acid and changes the genetic
code of the host (transduction), therefore the viruses cause genetic
variation within a host population, but may not cause disease.
Prion
 A virus without nucleic acid.
 protein infectious agent associated with several neurological diseases
(scrapie; kuru; Creutzfeld-Jakob syndrome; mad cow disease)









Maintain homeostasis
Organization
Growth and Development
Cellular organization
Heredity-- Contain genetic information
Acquire and use energy
Reproduction
Metabolism (use energy)
Responsiveness
We cannot see viruses with the naked eye
Are viruses living or nonliving?
Do they exhibit the characteristics of life?
What characteristics of life do viruses have?
video

Our main defense against viruses is
knowing how they are transmitted.
Obligate intracellular parasites-


they require a host cell to perform all
biological functions and reproduce.
No Independent Metabolism
Smaller than the tiniest bacteria-




20 to 250 nanometers (one nanometer
is one billionth of a meter)
http://www.cellsalive.com/howbig.
htm


Possess only one type
of nucleic acid

DNA or RNA, but
never both.
Eclipse Phase

period between
addition of virus and
the appearance of
assembled virus
progeny inside the
cell

Some viruses still
retain their
infectivity, even in
crystallized form









Polio
Influenza
The common cold
herpes
smallpox
Chickenpox
ebola
human
immunodeficiency
virus (HIV) causing
AIDS
H1N1




The CAPSID

the protein coat that encloses the
nucleic acid. This is the transport vehicle.
The CORE

made up of either DNA or RNA -this is
the part that actually infects the host cell.
SURFACE PROTEINS

external protein that recognizes one or
more receptor molecules on the host
cell. (The viruses ticket into a cell)
The VIRION

is the complete infective virus particle
that exists outside of a host cell.
overview
 Attachment
•Viral
components assemble
 virus attaches to cell
spontaneously

Infection within a host cell.
viral nucleic
acidconstruct
is inserted into
•The complete
viral
is
cell, capsid is abandoned
called
a virion.
 Replication of viral nucleic
acid
•The
virion is the completed,

viral genes are transcribed and
infective
virus particle.
translated
by host cell
 Synthesis of coat proteins
•A
virion can be either naked, or

aggregate around the new
enveloped.
strand of viral nucleic acid
 Assembly of progeny viruses
•An
enveloped virus is

hundreds are made
surrounded by a lipid bilayer
 Bursting
where
a naked virion has no
 liberating viral offspring to infect
layer. another cell




Contaminated fingers or droplets from coughs and sneezes
deposit the cold virus to the front of the nasal passages.
Small doses of virus (1-30 particles) are sufficient to produce
infection.
The virus is then transported to the back of the nose and onto the
adenoid area by the nose itself.
The virus then attaches to a receptor (ICAM-1) which is located on
the surface of nasal cells
•The receptor fits into a docking port
on the surface of the virus
•After attachment, virus is taken into
the cell where it starts an infection.
•New virus particles are produced.
•The infected cell dies and ruptures,
releasing newly made cold virus to
infect other cells in the nose and
start the process over again.




From the time a cold virus enters
the nose, it takes 8-12 hours for
the viral reproductive cycle to be
completed and for new cold
virus to be released in nasal
secretions.
This interval is called the
incubation period.
Cold symptoms can also begin
shortly after virus is first
produced in the nose (10-12
hours).
The time from the beginning of
the infection to the peak of
symptoms is typically 36-72
hours.


What is swine flu?
 Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A
influenza viruses that causes regular outbreaks in pigs.
 People do not normally get swine flu, but human infections can and do happen.
 Swine flu viruses have been reported to spread from person-to-person, but in the
past, this transmission was limited and not sustained beyond three people
What are the signs and symptoms of swine flu in people?
 The symptoms of swine flu in people are similar to the symptoms of regular
human flu and include
 fever, cough, sore throat, body aches, headache, chills and fatigue.
 Some people have reported diarrhea and vomiting associated with swine flu.
 In the past, severe illness (pneumonia and respiratory failure) and deaths have been
reported with swine flu infection in people.
 Like seasonal flu, swine flu may cause a worsening of underlying chronic medical
conditions.

How does swine flu spread?
 Spread of this swine influenza A (H1N1) virus is thought to be happening in the
same way that seasonal flu spreads.
 Flu viruses are spread mainly from person to person through coughing or sneezing
of people with influenza. Sometimes people may become infected by touching
something with flu viruses on it and then touching their mouth or nose.

Your body does have some natural ability to
inhibit viral infections, which is called
immunity. There are limited ways the body
fights viruses:



White blood cells engulf viruses in the blood and
"digest" them.
Antibodies- blood protein used to provide passive
immunity to some diseases
Interferons are proteins produced by cells when
exposed to a virus. This protein binds to the cell
membranes of neighboring cells and "interferes"
with the ability of a virus to enter the cell.

http://www.bam.gov/sub_diseases/diseases_
immuneplatoon.html



Outside the body, the "AIDS" virus, HIV, can be
destroyed with a 10% bleach solution - that is almost
weak enough for you to drink.
However, once inside a host, most substances that
destroy the virus are also harmful to the host.
Therefore, viral infections in animal cells can be
extremely hard to cure.

There are very few vaccines for viral infections
compared to the number of vaccines developed to
treat bacterial diseases.



Vaccines are a solution of weakened virus used to induce
the production of antibodies.
The first viral vaccinations were for measles, mumps, and
rubella.
There are now vaccines for hepatitis A and B, chickenpox,
smallpox, and rabies.



Virus vaccines are made with either inactivated
or attenuated viruses.
Inactivated viruses do not replicate in a host
cell.
Attenuated viruses have been genetically
altered so they are not able to cause disease.


Antiviral drugs: interfere with the synthesis of
viral nucleic acid or with the formation of viral
capsids during replication.
Antibiotics: specifically attack the metabolism of
a bacterial cell. Since viruses use only the
reproductive machinery of a cell, antibiotics are of
no use in destroying viruses.