Viruses and Public Health

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. 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. 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. 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.jpg; www.blc.arizona.edu/.../ Figures/Icos_Virus.GIF; http://www.foresight.org/Updates/Update48/Images/T4Schematic.jpg

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

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

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

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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?