Download Viruses

-VirusesAre non-living particles.
Most viruses are “pathogens”.
Pathogens are disease-causing agents.
Viruses are not Living Organisms
1. They are not made of cells
2. They are not capable of
carrying out any of the “life
Functions” on their own
Virology
is the study of viruses.
A “Virologist”
is a person who
studies viruses.
Viral History
Dimitri Iwanowski (1892) – discovered the
disease-causing juice in infected tobacco leaves
was “filterable”. (it passed through the filter)
Martinus Beijerinck (1898) – coined the term
“virus” (poison) and confirmed they are
filterable.
Wendell Stanley (1935) – isolated (with the
advantage of the newly developed Electron
Microscope) the particle causing tobacco
mosaic disease, crystallized it, and identified it
as a virus.
The First Vaccination
Dr. Edward Jenner's Inquiry, first published in 1798,
reported how, over a period of years, he had noticed
the immunity provided by cow-pox, and how he
decided deliberately to introduce the disease into a
patient to see if the effect could be artificially
produced. Soon afterwards, he would again inoculate
his patients, this time with live smallpox virus to see if
the cow-pox had worked. The "healthy boy" whom
Jenner, on May 14 1796, first vaccinated with virus
from the dairymaid Sarah Nelmes was James Phipps,
who proved Jenner's point by surviving repeated
unsuccessful attempts to infect him with smallpox.
Examples of Viruses
Colds
Polio
Herpes
Chickenpox
Rabies
Warts
Measles
Mumps
Rubella
Smallpox
Hepatitis
Shingles
Cowpox
HIV/AIDS
Hantavirus
Flu
West Nile
Ebola
Infectious Mononucleosis
Cancer
Viral Structures
All viruses have• A Nucleic acid core of DNA or RNA
• And a “capsid”. A capsid is a protective protein
coat made of protein units called capsomeres.
Some viruses also have• An Envelope, which is a membrane-like
structure outside the capsid that is usually made
of lipids.
• Projections = protein containing sugar chains
that attach the virus to the host cell.
Viral Classification
Viruses are grouped according to:
• whether they contain DNA or RNA
• their shape
• the organisms they affect
• their Size
• Etc…………
HIV
(Human Immunodeficiency Virus)
Envelope
Projections
Capsid
RNA
(made up of capsomeres)
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/HIV.gif
The T4 Bacteriophage
is a virus that destroys
(eats) bacteria.
http://www.aw-bc.com/mathews/ch24/fi24p22b.gif
Viruses Destroy cells.
The Lytic Cycle is the step by step
process by which a virus destroys a cell.
The Lytic Cycle has 5 steps.
A) Attachment- virus connects to host cell
B) Entry-nucleic acid is inserted into host cell
C) Replication-viral components are made
D) Assembly-new viruses are assembled
E) Release-host cell membranes are destroyed by
viral enzymes. New viruses are released and
free to destroy other cells.
The Lytic Cycle Pathway of the T4
Bacteriophage
2. Entry-nucleic acid is
inserted into host cell
3. Replication-viral
components are made
4. Assembly-new viruses
are assembled
1. Attachment: virus
connects to host cell
5. Release-host cell membranes are
destroyed by viral enzymes. New viruses are
released and free to destroy other cells.
The Lytic Cycle
The Lysogenic Cycle Pathway
A) Attachment-virus connects to host cell
B) Injection-viral nucleic acid is inserted
into host cell and is incorporated into the
host cell’s DNA as a Prophage. It can
remain dormant for days, months, or
even years.
C) Host cells replicate both the host cells
DNA and the Prophage.
D) The “new” host cells continue to survive.
Lysogenic Cycle
A) Attachmentvirus connects to
host cell
B) Injection-viral
nucleic acid is inserted
into host cell and is
incorporated into the
host cell’s DNA as a
Prophage. It can remain
dormant for days,
months, or even years.
C) Host cells
replicates both the
host cells DNA and
the Prophage.
D) The “new”
host cells
continue to
survive.
The Lysogenic Cycle
Radiation or chemicals can cause the
lysogenic cycle to change to the lytic cycle.
The Retrovirus Pathway
• The retrovirus has “RNA” as its
nucleic acid core, not DNA.
• Retroviruses contain an enzyme called
reverse transcriptase. Reverse
transcriptase converts RNA to DNA
• The viral DNA is then incorporated
into the host cell’s DNA
• The Lytic Cycle can then take place.
• HIV is a Retrovirus.
Viral Specificity
Most viruses require specific types of host
cells. They cannot infect any other cells.
For example:
Rabies infects and destroys nerve cells.
Hepatitis infects and destroys liver cells.
HIV infects and destroys T4 lymphocytes.
Spread of Viral Diseases
is called transmission.
Viral diseases can be
transmitted or transferred by:
1. Direct contact- touch or bites
2.
Indirect contact- contaminated food,
drinks or air, or contact with objects
that have viral particles on them….
Doorknobs, utensils, etc..
Viruses can also be spread by
Vectors
Vectors are “agents” which transfer
viruses from one host to another.
Examples of vectors include:
Mosquitoes: Which carry West Nile.
Mammals: Which carry Rabies.
Rodents: Which carry Hantavirus
Dual Host Viruses
Dual host viruses are viruses that can exist
in two very different host cell types.
Example: Equine Encephalitis
Horse
Mosquito
vector
Humans
Symptoms of West
Nile Fever
take as little as three to twelve days to show
up, and a few days to disappear.
•
•
•
•
•
Fever
Headache
body ache
swollen lymph glands
occasionally a rash on the trunk of the
body take as little as three to twelve days
to show up and a few days to disappear.
Viral Disease Prevention
Vaccines = the injection of materials that
stimulate the immune system; many
contain inactive or altered viruses
Quarantine = the isolation of infected
individuals, keeping them away from
healthy individuals
Vector Control = vaccinations of some
vectors, and extermination of others
Treatment of Viral Diseases
• Antiviral Drugs interfere with the
the synthesis of viral parts during
the lytic or lysogenic cycle.
• Antibiotics will NOT work against
viruses. They can only be used to
treat bacterial diseases.
Virus Origins
• Viruses probably de-evolved from the
first cells
• The first viruses could have been
naked bits of nucleic acid, like viroids,
that could travel from cell to cell
through damaged surfaces.