Discuss with the people around you the difference between these three words:

-Pathogen

-Infection

-Disease

-Epidemic

-Pandemic

Viruses are classified by:

• What type of genetic material they contain.

• Type of capsid that surrounds the nucleic acid.

• Presence of an envelope

• What types of cells or species it infects.

A pathogen is a disease-causing agent.

Once a pathogen, like a virus, begins multiplying inside cells or tissues, we call this an infection.

A disease occurs when defenses cannot be mobilized fast enough to keep the pathogen’s activities from interfering with body functions.

An epidemic is when a disease spreads fast through part of a population for a limited time, then subsides.

A pandemic is when an epidemic breaks out in several countries at the same time.

AIDS is a pandemic.

The first case reported in 1981,

it has been estimated that 1.1 million people are currently living with HIV in the U.S. today

(56,000 new REPORTED cases last year)

Currently, worldwide it is estimated 40.3 million are HIV positive.

● With a healthy immune system: 1000 to 1500 CD4 cells (Helper T cells)

● Once the CD4 count is below 200, the person is considered to have AIDS.

HIV - AIDS

• Lysogenic Cycle

• RNA retro-virus

• Infects helper T-cells

• Has a protective envelope

• Mutates at a high rate

• 10 different HIV strains, 1 super strain

• HIGHLY Preventable.

• Once inside a host cell, the retrovirus makes DNA from its RNA.

• To do this, it uses reverse transcriptase, an enzyme it carries inside its capsid.

What is a retrovirus?

• This enzyme helps produce double-stranded DNA from the viral RNA.

• Then the double-stranded viral DNA is integrated into the host cell’s chromosome and becomes a provirus.

Retrovirus Cycle

Exiting cell

Reverse transcriptase

Retrovirus

Enteringcell

RNA

RNA

DNA

DNA is made from the viral RNA.

mRNA

New virus parts

New virus forming

Provirus in host chromosome

Retrovirus

• The species specific characteristic of viruses is significant for controlling the

spread of viral diseases.

For example, smallpox was easier to eradicate because it only affects humans and since it is a DNA virus does

not mutate very often. (unlike the bird flu and West Nile that affect several

types of animals.)

Small pox

• Some viruses have been linked to certain cancers in humans and animals.

• These viruses disrupt the normal growth and division of cells in a host, causing abnormal growth and

creating tumors.

Cancer and Viruses

HPV

• The first virus to be identified was a plant virus, called tobacco mosaic virus, that causes disease in tobacco plants.

Tobacco mosaic virus causes yellow spots on tobacco leaves, making them unmarketable.

• Prions are thought to cause other neuron-proteins to fold themselves incorrectly, resulting in improper functioning.

Prions

• Prions are abnormal neuron-proteins that behave like viruses, but do not carry genetic information.

• Prions are responsible for many fatal degenerative diseases that first affect neural functioning, such as mad cow disease, its human equivalent: Creutzfeldt-Jakob disease, and kuru.

Prions

• Scrapie, a prion disease, causes sheep to by crazy and rub up against trees and posts until the scrape off their wool.

Prions

• Viroids are virus-like agents composed of a single circular strand of RNA with no protein coat.

• Viroids have been shown to cause infectious diseases in potatoes, citrus and other crop plants each year- causing millions of dollars in damage.

• The amount of viroid RNA is much less than the amount found in viruses.

Viroids