Chapter 20: Viruses and Prokaryotes

1. Chapter 20:Viruses and Prokaryotes Section 20-3: Diseases Caused by Bacteria and Viruses

2. Bacterial Diseases • Pathogens are microorganisms that cause disease • All known prokaryotic pathogens are bacteria • Louis Pasteur helped establish the germ theory of disease by showing bacteria responsible for many human and animal diseases • Bacterial diseases produced in 2 general ways: • Destroy living tissue of infected organism, directly or causing tissue damage by triggering immune system (bacteria that cause tuberculosis) • Release toxins that interfere with normal activity (bacteria that cause diphtheria, botulism)

3. Common Human Bacterial Diseases

4. Controlling Bacteria • Physical removal – washing hands or other surfaces under running water does not kill bacteria, but it can dislodge them (also viruses) • Disinfectants – chemical solutions that kill bacteria • Food storage – low temperatures slow bacterial growth, keep foods fresher than room temperature • Food processing – cooking kills bacteria • Heat sterilization – instruments are heated to above 100° C to kill bacteria

5. Preventing Bacterial Diseases • Vaccines are preparations of weakened or killed pathogens or inactivated toxins • When injected, vaccines prompt body to produce immunity to a specific disease

6. Treating Bacterial Diseases • Antibiotics such as penicillin and tetracylcine block the growth and reproduction of bacteria by disrupting proteins or cellular processes specific to bacterial cells without harming host • Ineffective against viral infections

7. Viral Diseases • Produce disease by disrupting homeostasis • Animal and plant diseases

8. Disease Mechanisms • Some attack and destroy specific cells, causing disease symptoms – poliovirus • Some viruses cause infected cells to change their growth and development patterns, sometimes leading to cancer

9. Preventing Viral Diseases • Vaccines • 1769- Smallpox vaccine, using cowpox virus • 1880s- Anthrax and rabies • 1923- tuberculosis • 1950s- 2 polio vaccines, one used killed viruses and one using weakened viruses • 1981- hepatitis B vaccine using recombinant DNA • 2006- vaccine against human papillomavirus (HPV) • Cold and flu viruses often spread by hand-to-mouth contact – wash hands, avoid contact with sick people, do not cough or sneeze on hands

10. Treating Viral Diseases • Few antiviral drugs • Attack specific viral enzymes host cells do not have

11. Emerging Diseases • Pathogens reproduce quickly, evolve easily • An unknown disease that appears in a population for the first time or a well-known disease that suddenly becomes harder to control is called an emerging disease

12. Emerging Diseases • Changes in lifestyle and commerce have made this a bigger issue • Tend to appear suddenly, resist control methods • Need better understanding of molecular structure and genetics

13. “Superbugs” • Evolution has created many bacteria that are resistant to antibiotics • In the 1940s, penicillin killed everything • Widespread use of antibiotics has allowed for natural selection to favor resistance, and conjugation can transfer drug-resistant genes

14. MRSA

15. New Viruses • Reproduce so quickly, so simple genetically they can jump species (SIV to HIV) • Flu virus is always changing – new vaccines and variations (bird flu)

16. Prions • 1972- Stanley Prusiner investigated cause of scrapie, an infectious disease in sheep • Experiments showed clumps of protein particles in the brains of infected sheep. • Prusiner called particles prions, short for “protein infectious particles” • Misfolded proteins in the brain cause a chain reaction of misfolding in other normal proteins, clogging the brain tissue and causing disease • Mad cow disease