2. Diseases caused by bacteria and viruses
Section 20.3

3. What is a pathogen? A Pathogen is a disease causing agent
Many things can be a pathogen, but Bacteria and Viruses are the most common
Louis Pasteur – first person to show that bacteria can cause disease
Helped establish Germ Theory
Bacteria are responsible for a number of human diseases

4. How does a Bacterial Disease work?
Bacteria cause disease in one of two ways
They either:
1) Destroy living cells
Example – bacterium that causes tuberculosis
Inhaled into lungs, and can cause immune response, destroy large areas of tissue. Can travel in blood to other parts of the body
2) Release chemicals that upset homeostasis
Example – species that causes Diphtheria , and species that causes Botulism
Diphtheria has largely been eliminated in developed countries due to vaccination
Botulism does still sometime claim lives

5. Human Bacterial diseases

6. How can you control Bacteria?
Although most are harmless, there are many steps that can be taken to reduce the risk of bacterial infection
1) Washing hand with soap and water helps remove pathogens
2) Disinfectants kill bacteria
3) Storing food in a fridge slows down bacterial growth
4) Cooking food kills many bacteria
5) Sterilization by heat

7. Preventing and treating bacterial disease
Prevention – by vaccination
How do vaccinations work?
Body’s immune system is stimulated by a vaccine, which is either weakened or killed pathogens
Gives the body the ability to destroy pathogens if encountered again – immunity!
Treatment – antibiotics
A large number of drugs can be used to attack a bacterial infection
Antibiotics block the growth and reproduction of bacteria
Disrupt proteins specific to bacteria, do not harm the host

8. How do viruses cause disease?
Viruses disrupt the bodies normal homeostasis

9. Viral disease mechanisms
Viruses often attack and destroy certain cells in the body, causing the symptoms of the associated disease
Poliovirus destroys cells in the nervous system, leading to paralysis
Other viruses can cause cells to change patterns of growth – leading to cancer
Viruses directly destroy living cells, or affect cellular processes in ways that upset homeostasis

10. Preventing and treating viral disease
Vaccinations again key to prevention
BUT, personal hygiene is also important
Antibiotics do not work on viral diseases
BUT some antiviral drugs have had success attacking specific viral enzymes
Can be used to speed recovery from the flu, or prolong the life of people infected with HIV

11. What is the risk of emerging diseases?
Pathogens can evolve rapidly
Emerging disease – unknown disease that appears in a population for the first time, or a well known disease that suddenly becomes harder to control
Threatening to human health, as human populations have little to no resistance to them, and control methods haven’t been developed

12. Superbugs
In the 1940s penicillin was a wonder drug – infections were cured almost immediately, but now that is less affective - why?
Superbugs have evolved are resistant to whole groups of antibiotics AND spread their genetic immunity to other populations through conjugation
MRSA – common example. Especially in hospitals

13. New Viruses
Viruses evolve so quickly that they can sometimes jump from one host species to another
AIDS is thought to have originated in non human primates
Bird flu causes worry – as some instances a bird flu appears very similar to the most deadly form of human flu
Some cases bird flu can infect humans
Not just birds – H1N1 (swine flu a few years ago)
Still possible that there may be a major jump into human populations in the future

14. Prions Stands for protein infectious particles
Formed when a protein (PRP) is inproperly folded
Prions can damage nerve cells
Discovered in 1972 by Stanley Prusiner, a researcher who was investigating scrapie, and infectious disease in sheep.
Link to BSE (mad cow disease in UK)

15. Key points questions
How do bacteria cause disease? How can bacterial disease be both prevented and treated?
How do viruses cause disease? How can viral disease be both prevented and treated?
Why are emerging diseases threatening to human health?

16. Key points
Bacteria cause disease by destroying living cells or releasing chemicals that disturb homeostasis
Bacterial disease can be avoided through washing hand, disinfecting, heat treating etc…
Prevention – vaccination
Treatment – antibiotics
`viral diseases destroy living cells or they affect cellular processes to upset homeostasis
Treatment – Some antiviral drugs
Emerging disease – unknown disease that appears in a population for the first time, or a well known disease that suddenly becomes harder to control
Human populations have little to no resistance

17. Vaccinations in society
Read page 593 in the textbook, and think about the following questions –
What is the advantage of having a set policy regarding required vaccines for all students entering school?
How do laws and regulations requiring vaccines impact both public health and the health of the individual?