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