Chap. 24:Viruses Ex. Cold, polio, rabies, herpes, AIDS, small pox, flu, cancers, mono, chicken pox, HPV, Ebola, SARS, West Nile, Mad-Cows Disease, etc.

I. Terminology Virology – study of viruses Virulent – when a virus causes a disease Temperate – when a virus doesn’t cause disease right away (AIDS, cancer) Obligate intracellular parasite – (virus) must use a host for reproducing Nanometer (nm) – measurement for virus can fit within a typed “o”

- Viroid – smaller than a virus – contains only a single strand of RNA Prion – contains about 250 amino acids – no nucleic acid. Causes long term diseases like Kuru. Bacteriophage – virus that attacks bacteria (also called phages) Oncogenes – genes that cause abnormal cell growth (tumors, aka cancer) II. Structure - classified by either having DNA or RNA not by binomial nomenclature. - classified by either having DNA or RNA not by binomial nomenclature.

-- RNA viruses contain reverse transcriptase an enzyme that changes RNA to DNA – called retroviruses.

III. Viral Cycles 1. Lysogenic Cycles a. Tail fibers attach to cell a. Tail fibers attach to cell b. Nucleic acid injected into host b. Nucleic acid injected into host c. Nucleic acid attaches to host nucleic acid to become a prophage d. Doesn’t cause harm immediately but at some point it can become the lytic cycle. e. Causes transduction (spreading of new DNA to another cell) ex. Cancers,cold sores,shingles, AIDS

2. Lytic Cycle – immediate taking over of a host cell. a.Attachment – virus attaches tail fibers down onto host cell membrane. b.Entry – DNA/RNA is injected into cell. c.Replication – viral DNA/RNA tells host cell to make more viruses d.Assembly – making of more viruses e.Lysis (release) – host cell ruptures and releases all viruses to go and infect new cells. -- interferon – chemical released by host cell upon rupture to signal neighboring cells of virus -- interferon – chemical released by host cell upon rupture to signal neighboring cells of virus

IV. Transmitting of viruses Vector – organism that transmits a virus – usually an arthropod (insect) ex. Tick, mosquito, flea Viral reservoir – place where virus originated --- viruses are transmitted by : air, exchange of body fluids, direct contact, water --- viruses are transmitted by : air, exchange of body fluids, direct contact, water

A. Viral Control 1. vaccination – given inactivated (dead or diluted amount) or attenuated (genetically altered) virus Result : Antibodies – made by body to recognize and destroy virus ---- Result : Antibodies – made by body to recognize and destroy virus 2. Antiviral drugs – drugs that interfere with viral making. Ex. AZT for AIDS

*** Antibiotics do not work on viruses because they are made to target the cell processes of a bacteria Pandemic – when a disease spreads across the world. Ex. AIDS Endemic – disease isolated to a specifc region. Ex. Ebola Epidemic – rapid spreading of a disease and affecting many. Ex. Influenza 1918