Viruses Ebola Influenza Rabies HIV West Nile Virus

Why Study Viruses? Cause diseases Damage living things May be fatal

General Characteristics 1.Very small - 10 -1000 nanometers - 10 – 1000 x 10 -9 m -Need electron microscope to view

General Characteristics 2. Various Shapes

General Characteristics Protein Coat 3. Structure = Two Parts: Nucleic acid + Protein Coat (Capsid) Nucleic Acid

General Characteristics 4. Acellular - no cell - no organelles - no metabolism - cannot be killed with antibiotics

General Characteristics 5. Nucleic acid - Has DNA - or RNA (retro viruses) - (never both) DNA RNA

General Characteristics Nucleic Acids 1. DNA = deoxyribonucleic acid - Double strand - Contains genes for making viral proteins (requires 2 steps)

General Characteristics Nucleic Acids 2. RNA – ribonucleic acid - Single strand - Retro virus - contains code for directly producing viral proteins ?s 1-7

General Characteristics 6. Mutates very easily - no cell - no protection from mutagens E.g. chemicals, radiation, uv light exposure

General Characteristics 7. Virus = Latin for poison

Examples of Viruses Ebola Hanta HPV (Human papilloma virus)* Mumps Common Cold Polio Rabies HIV Hepatitis A,B*,& C Herpes ( E.g. Chicken pox) Measles Smallpox Ebola Hanta HPV (Human papilloma virus)* Mumps Rubella Epstein-Barr* SARS * can cause cancer

Viral Cycles Two Types of Viral Cycles 1. Lytic 2. Lysogenic

Lytic Cycle Immediate viral replication Injection/Infection-Viral DNA into host cell Synthesis & Assembly of virus Cell lysis (rupture) = tissue damage New viruses emerge to infect new cells

Lysogenic Cycle Viral replication is delayed Viral DNA put into host genome Host cells divide, including viral genes 3. When organism is stressed → → lytic cycle begins → viral replication (cell lysis) etc.

Lytic vs Lysogenic Cycle New viruses emerge Viral DNA Bacterial genome Injection Lysis Assembly Many divisions Synthesis

How do Viruses do Harm? Possible effects: 1. Lyse cells (Tissue damage) 2. Release viral toxins (poisons) 3. Prevent host’s cell division 4. Disrupt formation of host chromosomes

How do Viruses do Harm? ?s 8-13 5. Can cause uncontrolled cell division (cancer) 6. Can cause changes in cell membrane (immune system destroys host cells) ?s 8-13

Prevention Vaccines Live or killed virus injected Host immune system makes antibodies When infected, host immune system ready to kill virus

Treatment Antiviral drugs Interfere with viral replication E.g. AZT ( for AIDS) E.g. Interferon (for Hepatitis C) 2. Supportive Therapy Reduce fever (E.g. aspirin, Tamiflu) Make host comfortable Wait until virus runs its course ?s 14-16

Viroids Nucleic acid (RNA) only No protein coat Common in plants

Prions Protein only No nucleic acid Replicate by bumping proteins, causing refolding in shape of prion Cause diseases of nervous system

Prions E.g. Bovine Spongiform Encephalopathy (BSE – a.k.a. Mad cow disease) Kreutzfeld-Jakob’s disease (in humans)

Prions 2. Chronic wasting disease Deer and elk

Prions 3. Scrapie – usually fatal sheep disease

Prions 4. Kuru – destroys human nervous system Papua New Guinea Headhunters (cannibalistic tribes) Word to your mama!

What are the Modes of Transmission of a Virus? How does a virus spread? Direct contact (Touch) Contaminated food, water or body fluids (e.g. from blood, saliva, or semen) Animal bite (body fluids) Sexual contact (body fluids)

Examples of Modes of Transmission Disease Mode of Transmission Symptoms Chicken Pox inhalation Rash, fever Influenza Headache, muscle aches, sore throat, cough HIV/ AIDS Contaminated body fluids Immune system failure Rabies Animal bite Madness, death

Viruses Are they living or nonliving ? Are they smart nucleic acids? Why can’t we kill them? ?s 18-22