-viruses- are non-living particles. most viruses are “pathogens”. pathogens are disease-causing...

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-Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents.

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Page 1: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

-Viruses-Are non-living particles.

Most viruses are “pathogens”.

Pathogens are disease-causing agents.

Page 2: -Viruses- Are 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

Page 3: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Virology

A “Virologist”

is a person who studies viruses.

is the study of viruses.

Page 4: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Viral HistoryDimitri 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.

Page 5: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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.

Page 6: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Examples of VirusesColds Polio Herpes

Chickenpox Rabies Warts

Measles Mumps Rubella

Smallpox Hepatitis Shingles

Cowpox HIV/AIDS Hantavirus

Flu West Nile Ebola

Infectious Mononucleosis Cancer

Page 7: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Viral StructuresAll 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.

Page 8: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Viral ClassificationViruses are grouped according to:• whether they contain DNA or RNA• their shape• the organisms they affect• their Size• Etc…………

Page 9: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

HIV(Human Immunodeficiency Virus)

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/HIV.gif

RNA

Projections

Capsid(made up of capsomeres)

Envelope

Page 10: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

http://www.aw-bc.com/mathews/ch24/fi24p22b.gif

The T4 Bacteriophageis a virus that destroys

(eats) bacteria.

Page 11: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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.

Page 12: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

1. Attachment: virus connects to host cell

2. Entry-nucleic acid is inserted into host cell 3. Replication-viral

components are made

4. Assembly-new viruses are assembled

The Lytic Cycle Pathway of the T4 Bacteriophage

5. Release-host cell membranes are destroyed by viral enzymes. New viruses are

released and free to destroy other cells.

Page 13: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

The Lytic Cycle

Page 14: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

The Lysogenic Cycle PathwayA) Attachment-virus connects to host cellB) 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.

Page 15: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Lysogenic Cycle

A) Attachment-virus connects to

host cell

C) Host cells replicates both the host cells DNA and

the Prophage.

D) The “new” host cells

continue to survive.

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.

Page 16: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

The Lysogenic Cycle

Page 17: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Radiation or chemicals can cause the lysogenic cycle to change to the lytic cycle.

Page 18: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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.

Page 19: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Viral SpecificityMost 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.

Page 20: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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..

Page 21: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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

Page 22: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

Dual Host Viruses

Dual host viruses are viruses that can exist in two very different host cell types.

Example: Equine Encephalitis

Horse HumansMosquitovector

Page 23: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents
Page 24: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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.

Page 25: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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

Page 26: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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.

Page 27: -Viruses- Are non-living particles. Most viruses are “pathogens”. Pathogens are disease-causing agents

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.