1. 1 Viruses and Public Health Viruses are responsible for >50% of infectious diseases.  What are they? Are they alive? Infectious diseases are those that are caused by microbes  Bacteria, viruses, a few fungi, and a few protists  What are significant diseases? How are they spread? What is our protection?

2. 2 Viruses Most biologists do not consider viruses to be alive because  They are not made of cells.  They cannot reproduce without a host cell.  Plus other excuses. Not made of cells  This means that antibiotics which attack cell function are of no use. Certain drugs work. Obligate intracellular parasites  Must reproduce within a host cell.

3. 3 What are viruses made of Nucleic acid  Even though they aren’t cells, they still need a genetic blueprint so they can reproduce.  Viruses may have ds DNA, ss DNA, ds RNA, or ssRNA, depending on the virus. A covering called a capsid  A layer of protein which protects the nucleic acid and gives the virus its shape.

4. 4 Viral size and shape Viruses range from 30 nm to 300 nm  Ribosomes are about 30 nm  The smallest known bacteria are about 200 nm Viral shapes:  helical, polyhedral, and complex http://www.glencoe.com/qe/images/b136/q4323/ch18_0_a.jpghttp://www.glencoe.com/qe/images/b136/q4323/ch18_0_a.jpg; www.blc.arizona.edu/.../ Figures/Icos_Virus.GIF; http://www.foresight.org/Updates/Update48/Images/T4Schematic.jpg

5. 5 Examples of virus shapes http://www-cgi.cnn.com/HEALTH/9604/16/nfm/ebola.levine/ebola.reston.large.jpghttp://www-cgi.cnn.com/HEALTH/9604/16/nfm/ebola.levine/ebola.reston.large.jpg; http://www.virology.net/Big_Virology/EM/Adeno-FD.jpg EbolaAdenovirus

6. 6 Life Cycle of a virus http://web.uct.ac.za/depts/mmi/jmoodie/flu2life.gif

7. 7 Can you catch any virus? We think that every living thing, bacteria included, has a virus that infects it. But viruses are specific  Infect only certain types of organisms  Infect only certain types of cells  Attachment requires a match of molecules between the virus and host cell.

8. 8 How do you grow viruses? Can’t grow them in a Petri dish! Need a host cell. Animal models or human volunteers  Ethical limits re using humans Eggs  In bulk for vaccination material Cell culture  Viruses grow on cells living in a dish

9. 9 Ways to grow viruses http://www.fao.org/ag/againfo/foto/egg-facts.gif http://www.fao.org/ag/againfo/foto/egg-facts.gif news.bbc.co.uk/.../_230333_cell_culture_300.jpg

10. 10 How do viruses cause disease? Viruses damage cells  Viruses use host cells energy  Viruses break open host cells when they multiply  Cells die Your immune system kills infected cells  White blood cells called T cells kill infected cells before too many viruses multiply Viruses cause birth defects  Virus kills important cells in embryo

11. 11 Do viruses cause cancer? Some do.  Can’t prove causation because can’t infect humans with viruses to cause cancer.  Hepatitis B: liver cancer  Kaposi’s sarcoma virus: cancer with AIDS  Papilloma virus: genital warts and cervical cancer  Epstein-Bar virus: mononucleosis and Burkitt’s lymphoma

12. 12 Lots of familiar diseases are caused by viruses Measles, chicken pox, polio Herpes, AIDS, Mono SARS, West Nile Influenza, smallpox, rabies Common cold, Warts Parvo, 24 hour stomach “flu”

13. 13 How do you catch diseases? Bacterial, viral, and other microbes Microbes that cause disease are found somewhere: a reservoir  Could be other humans, could be animals, could be soil or water. To cause disease, microbe must get from the reservoir to you  If you are part of the cycle of infection, microbe must then get to others.

14. 14 Transmission Microbe needs to get from reservoir to you. Contact  Direct contact: touching, kissing, sex, endogenous spread (one part of you to another)  Indirect contact, via fomites (inanimate objects)  Droplet transmission: less than 1 meter thru air http://students.washington.edu/grant/random /sneeze.jpg

15. 15 Transmission-2 Vehicles  Water: various viruses, bacteria, protozoa, mostly that cause diarrhea and enter water supply.  Food: unpasteurized or contaminated food, either improperly grown, processed, or prepared.  Airborne: microbes attached to dust, skin flakes, dried mucus become aerosols, travel thru air. http://www.kennethkeith.com/milkgreeceb.JPG

16. 16 Transmission-3 Vectors  Typically arthropods (insects, ticks)  Mechanical vectors: simply spread disease, e.g. houseflies walking on feces, spread germs to humans.  Biological: pathogen goes through part of life cycle in vector Viruses or protozoa that reproduce within mosquito, e.g. Major method for spread of zoonoses. http://www.doktordoom.com/images/Tick.jpg

17. 17 Locally and Internationally important diseases The Commonplace  Minor respiratory diseases, i.e. common cold, spread by contact.  Digestive system: contaminated food, water; unhygienic bathroom behavior and contact. Regional  The highest incidence of tularemia, a bacterial disease, is the Ozark Mts.

18. 18 The Embarrassing: STDs  Syphilis, gonorrhoea, chlamydia all bacterial diseases that can be cured with antibiotics.  Herpes, genital warts, HIV are viral Herpes is forever, wart virus causes cancer, HIV causes death  The spread of STDs can be controlled by change in behavior.

19. 19 International  HIV is ravaging parts of the world, especially Africa. Social, political, economic factors are all involved.  Malaria, caused by a protozoan, is still #1 cause of misery throughout the world.  Lack of clean water, whether from poverty or natural disaster, results in fecal-oral transmission; bacterial diseases such as typhoid fever, cholera, E. coli and viral diseases like Hepatitis A.

20. 20 New and Emerging Diseases: challenge for scientists AIDS since 1970s Legionnaire’s disease since 1976 Ebola just as recent West Nile spread to and thru US in last 5 years Ready for next flu pandemic? Is bird flu it?