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Viruses

Virus in latin means, “poison” Definition- Infectious non-living particle

that duplicates in the cells of an infected host.

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Other definitions

Epidemic- A disease that is prevalently occurring in a small geographic area

Pandemic- A disease that is prevalently occurring over a wide geographic area

Vaccine- A preventative treatment used to provide immunity to a bacteria or virus

Eradicate- To get rid of completely

Antibody- Proteins created in blood and body tissue by the immune system to neutralize or destroy sources of disease.

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Why don’t we call viruses living?They :

1. Are not made up of cells

2. Don’t eat

3. Don’t grow

4. Carry out biological functions (breathing)

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A virus is surrounded by a capsid (protein coat) which determines the shape of the virus.

The capsid contains nucleic acids (either DNA or RNA).

Tail fibers

for attachment to host cell.

Replication (making copies)

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Viruses replicate in one of two ways: Lytic- The virus invades the host cell and

commands it to make new viruses, then the cell bursts and releases the new viruses.

Lysogenic- The virus invades a bacterial cell and merges its DNA with the bacterial cell’s DNA, then as the bacteria replicate, the virus is replicated.

Lytic cycle

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Virus injects its DNA

Virus DNA commands host cell to make new viral partsNew viral parts

assembled

Cell lyses (breaks apart) and new viruses are released

Virus attaches to host cell.

Lysogenic Cycle

8http://www.howstuffworks.com/virus-human2.htm

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Disease Transmission SymptomsCommonCold

Inhalation, direct contact

Sinus congestion, muscle aches, cough, fever

Smallpox

Inhalation Blisters, lesions, fever, blindness, scars; often fatal

Influenza(Flu)

Inhalation Headache, muscle ache, sore throat, cough, fatigue, fever, chills

Warts Direct contact Lumps on skin or mucus membranes

Tobacco Mosaic Virus

Direct contact (of sap)

Molting and discoloration of leaves

Viral Diseases

Treatment There are not cures for viral diseases You can not treat a virus with antibiotics

However… Some viruses can be prevented through the use of

vaccines.

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Vaccines

Vaccines Vaccines containcontain

weakened weakened or killed or killed strain of strain of the virusthe virus

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How Vaccines Work:1. Weakened or killed

virus enters the body (nasal spray or injection)

2. Your body responds to it by making antibodies.

3. Then, when your body comes in contact with the viruses later you don’t become symptomatic, you are immune.

What about Tamiflu? Not a vaccine Tamiflu targets a protein on the flu virus

cells. Normally, this protein helps the flu virus

break through the cell walls so it can move on to other cells and replicate itself.

Tamiflu stops the protein from doing this, so that the virus can't leave the cell to infect other cells.

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Example: Seasonal Flu Each seasonal influenza vaccine contains three influenza

viruses. The viruses in the vaccine change each year based on international surveillance and scientists' estimations about which types and strains of viruses will circulate in a given year. About 2 weeks after vaccination, antibodies that provide protection against influenza virus infection develop in the body.

The "flu shot" — an inactivated vaccine (containing killed virus) that is given with a needle, usually in the arm.

The nasal-spray flu vaccine — a vaccine made with live, weakened flu viruses that do not cause the flu

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What about 2009 H1N1?

Viruses are ever-changing The H1N1 virus is basically a novel

(new) strain (version) of the flu that humans don’t yet have any antibodies to.

Scientists have now isolated and created a vaccination for the 2009 H1N1 virus.

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