1. 20.3 Diseases Caused by Viruses and Bacteria
How do bacteria cause disease?
How do viruses cause disease?
Why are emerging diseases particularly threatening to human health?

2. Vocabulary
Pathogen
Vaccine
Antibiotic
Emerging disease
Prion

3. Pathogen A Pathogen is an organism that causes disease.
Microorganisms that cause disease are bacteria and viruses.
Archaea do not cause disease.

4. How do bacteria cause disease?
Bacteria cause disease by destroying living cells or by releasing chemicals that upset homeostasis.
Examples: Tuberculosis damages tissues in the lungs and Tetanus releases toxins that upset homeostasis

5. Tuberculosis
The pathogen infects the lungs and the body’s immune response causes damage to the tissues of the lungs
Example of disease caused by cell destruction
Mycobacterium Tuberculosis

6. Tetanus
Bacteria produce disease by releasing toxins into the system
Spores of the pathogen enter the body and produce a toxin that blocks nerve signals
Clostridium tetani (C. tetani). --> tetanospasmin --> severe muscle spasms/lockjaw

7. Controlling Bacteria There are several ways to control bacteria
Physical removal
Disinfection
Food Storage
Food Processing
Sterilization by Heat

8. Physical Removal
Washing hands with soap and water helps dislodge bacteria and viruses
Scrub hands for seconds will remove viruses and bacteria from your hands

9. Disinfectants
Disinfectants are chemical solutions that kill bacteria and can be used to clean surfaces.

10. Food Storage
Low temperatures in refrigerators and freezers slow bacterial growth

11. Food Processing
Cooking food (frying, boiling, or steaming for example) can destroy bacteria.
Example: Spinach E. Coli outbreak in 2006 raw spinach and lettuce carried disease while the cooked was safe.
Esherichia Coli --> release Shiga, a toxin that inhibits protein synthesis

12. Sterilization by Heat
Heating objects to 100 degrees Celsius will kill most bacteria
Medical equipment is heated to higher temperatures.

13. Preventing Disease
In addition to controlling bacteria, many bacterial diseases can be prevented through the use of vaccines.
A vaccine is a preparation of weakened or killed pathogens or inactivated toxins.
This preparation helps a body produce immunity to a specific disease.
Can prevent diseases caused by bacteria or viruses.

14. Treating Bacterial Diseases
Antibiotics: drugs that are used to attack a bacterial infection. Antibiotics disrupt processes that bacteria use to survive and reproduce.
Antibiotics are essentially selective poisons that target bacteria without damaging our cells
Bactericidal Antibiotic: kills the bacteria
Bacteriostatic Antibiotic: stops the bacteria from multiplying
Selective poison: target the building of cell walls or synthesis of folic acid (two processes that bacteria perform that our cells do not), attack peptidoglycan.

15. Antibiotic Examples
Penicillin: disrupts the formation of peptidoglycans and weakens the cell wall of bacteria so that they rupture.
Sulfa Drugs stop bacteria from producing folic acid that they need to survive
Tetracycline inhibits bacterial growth by stopping protein synthesis

16. Viral Diseases How do viruses cause disease?
Viruses cause disease by directly destroying living cells or by affecting cellular processes in ways that upset homeostasis

17. Preventing Viral Diseases
Use of vaccines
Example: 1950 Polio Vaccine that uses a weakened virus
Wash your hands
Coughing or sneezing into a tissue rather than into your hand

18. Treating Viral Diseases
Cannot be treated with antibiotics
There are some antiviral drugs, for example: Amantadine for treating the flu.
Antiviral drugs attack specific enzymes that the viruses need to survive, and that human cells do not have.

19. Emerging Diseases Emerging Diseases
An unknown disease that appears in the human population for the first time or a well-known disease that becomes harder to control

20. Examples of Emerging Diseases
Multidrug Resistant Tuberculosis
West Nile Virus
Bird Flu

21. Why are emerging diseases particularly threatening to human health?
Emerging diseases are a threat to human health because we have poor resistance to these diseases and have not yet developed methods to control the pathogens that cause emerging diseases.

22. “Superbugs”
The widespread use of antibiotics has lead to the emergence of pathogens that are resistant to the drugs we develop to fight them
MRSA for example
H5N1 Bird flu is a new virus that would have to make few changes in order to jump from birds to humans and resembles the flu viruses of the past that have caused pandemics.

23. Prions
Prions:
protein
infectious
particles.

24. Prions
Discovered in 1972 when scientists were researching a disease in sheep called “Scrapie”
Prions are misfolded proteins that are either ingested (eaten) or are caused by mutation
Prions build up in nerve cells in infected people and animals until the cells no longer function.

25. 20.3 Diseases Caused by Bacteria and Viruses