1. Viruses Nonliving Pathogens

2. Viruses Pathogen (infectious agent) – any living organisms or particle that can cause infectious disease Can be living or nonliving Living Pathogens: 1. Prokaryotes (Bacteria) 2. Eukaryotes – typically protists and fungi

3. Viruses Characteristics of Living – reproduce (genetic material), use nutrients and energy, grow and develop, respond to environment

4. Viruses Nonliving Pathogens: 1. Viruses are not considered living – have some characteristics of living organisms -reproduce (have genetic material) but cannot reproduce on their own – need a host cell -infectious particle made only of a strand of DNA or RNA surrounded by protein coat 2. Viroid -infectious particle that causes disease in plants, single-stranded RNA without a protein coat, passed by seed or pollen

5. Viruses 3. Prion – infectious particle made only of proteins that can cause other proteins to fold incorrectly -unusual because do not contain genetic material -cause diseases of brain like mad cow disease incubate with no effect, worse quickly and are fatal – body has no response to the invading protein

6. Viruses Virus – comes from Latin “poison” Viruses, prions and viroids are very small Eukaryotic cells 10,000 – 100,000 nm Prokaryotic cells 200– 10,000 nm Prion 2–10 nm Viroid 5-150nm Virus 50-200 nm Draw a line between living and nonliving. Lightly shade living green and nonliving black.

7. Viruses Structure of Viruses Virion – single viral particle, contains genetic material and a protein shell or capsid Lipid envelope – (not all viruses) protective outer coat of a virus, spiky structures made of proteins and sugars Viral Infections are specific to a particular type of cell The shape of the virus can tell scientists which type of cell the virus will harm

8. Viruses 1. helical (spring like) Example Bacteriophage – a virus that attacks bacteria 2.polyhedral or many- sided Example foot-and- mouth disease 3. enveloped Example Influenza – the virus that causes the flu

9. Viruses Viral Reproduction 2 Types of Viral Infections: Lytic and Lysogenic

10. Viruses 1. Lytic –(active) host cell bursts, releasing new viral offspring into the host’s system, new offspring infect more cells Click for Video

11. Viruses 2. Lysogenic – (sleeping) viral DNA combines with host cell’s DNA, the infected DNA is replicated using the host’s cell’s reproductive process (mitosis) and each new daughter cell is infected, it can change the cell’s traits Stress, illness, weak immune system will activate lysogenic viruses When activated the cycle moves to lytic Click for video

12. Viruses Examples of illnesses caused by viruses common cold: More than 200 viruses are known to cause a cold; no vaccine -hard to find cure with many different viruses -cold viruses can mutate as they move from one person to another

13. Viruses Influenza (flu): spreads quickly, can result in frequent local epidemics; vaccine available -epidemic - rapid outbreak of an infection that affects many people. -mutates easily - new influenza vaccine to be made every year -vaccine - substance that stimulates the body’s own immune response against invasion by infectious agents.

14. Viruses SARS: Severe acute respiratory syndrome (SARS) - has symptoms similar to influenza, such as fever and coughing or difficulty in breathing; no vaccine - it first appeared in late 2002

15. Viruses HIV: Human immunodeficiency virus -transmitted by body fluids (sexually transmitted, blood transfusion, sharing needles); no vaccine -retrovirus. Retro- means “backward,” which describes how retroviruses work -contains RNA and uses an enzyme called reverse transcriptase to make a DNA copy

16. Viruses -active HIV infection destroys white blood cells of the host’s immune system -loss of white blood cells ultimately causes AIDS, acquired immune deficiency syndrome -weakened immune system makes it hard to fight off even the common microorganisms that humans encounter every day.

17. Viruses -HIV enters the human cell by endocytosis – tricks the cell into letting it in, the receptors match the host cell’s receptors -releases from the host cell by “budding” – the HIV virus emerges from the cell membrane

18. Viruses Chicken pox: rash, itchy skin, fever -transmitted by contact, or droplet inhalation; vaccine available Hepatitis A: yellow skin, fatigue, abdominal pain -transmitted by contact with contaminated feces; vaccine available Mumps: painful swelling in salivary glands, fever -transmitted by droplet inhalation; vaccine available

19. Viruses Rabies: anxiety, paralysis, fear of water -transmitted by bite of infected animal; vaccine available West Nile: fever, headache and body ache; -transmitted from bite of infected mosquito; no vaccine

20. Viruses Preventing Viruses There is no medication for viruses. If you get a virus, the doctor can only treat the symptoms. The only defense against a virus is to prevent the illness through vaccination. Vaccines - can prevent some, but not all, viral diseases -made from the same pathogen—disease-causing agent—that it is supposed to protect against --consist of weakened versions of the virus, or parts of the virus, that will cause the body to produce a response -Helps build up the immune system -works by preparing the host’s immune system for a future attack

21. Viruses Viruses in the News Zika Virus Ebola Virus