1. Defense Against Infectious Diseases
6.3

2. 6.3 Pathogens An organism or virus that causes a disease
Viruses, bacteria, fungi, protozoa, flatworms, and roundworms can all be pathogens

3. Examples include:
Viruses – Rhinovirus (causes the common cold), HIV, HCB (Hepatitis B virus)
Bacteria – Staphylococcus (causes strep throat), Vibrio Cholerae (causes cholera), Myobacterium tuberculosis (causes TB)
Fungi – Candida (yeast infections), Trichophyton (fungus that causes ringworm)

4. The Common Cold

5. Methods of transmission
Cuts in the skin
Mouth, Nose, and Eyes
Vectors (animals that transmit disease)
Sexual Transmission
IV Drug Use
Blood Transfusions
Food and Water

6. 6.3 Barriers to infections
First line of defense: prevent pathogens from entering the blood stream
Skin
The skin is a tough, impenetrable physical barrier
Skin has a lower pH which make it inhospitable for many bacteria
Sweat has lysozymes (special enzymes) that destroy bacteria

7. When Skin is Broken
When the skin is broken we lose the primary line of defense for our body.
Cuts in the skin are sealed by blood clotting
Clotting factors are released from the platelets in the blood.
Thrombin –
Hormone that triggers
a cascade of reactions
that convert fibrogen
to fibrin.

8. 6.3 Mucous membranes Traps pathogens because it is sticky
Cilia in the throat sweep up bacteria and allow them to be swallowed and then destroyed by acid in the stomach
Contains phagocytes (white blood cells that ingest and destroy pathogens)

9. Leucocyte (white blood cell)
6.3
Leucocyte (white blood cell)
Phagocyte (large)
macrophage
neutrophil
Lymphocyte (small)
T-cell
B-Cell

10. 6.3
Cellular Defense
Second line of defense is the non-specific immune system - a host of quick, non-specific methods of killing microbes that have entered the body.
Leucocytes = general category of white blood cells
Phagocytes: large, irregularly-shaped leukocyte cells that remove bacteria, viruses, cellular debris and dust particles.

11. 6.3
Are constantly changing shape, and they flow over pathogens, surrounding and ingesting them through the process of phagocytosis to form a phagosome
Enzymes within the lysosome of the phagosome break down the pathogen
Different phagocyte cells work in different locations:
neutrophils circulate in the blood
macrophages are found in lymph, tissue fluid, lungs and other spaces, where they kill microbes before they enter the blood

12. 6.3

14. Now that you have gotten infected
Antibiotics
Work on bacteria, not viruses
Antibiotics block specific metabolic pathways found in bacteria, but not in eukaryotic cells (such as our own)
Examples: RNA replication, transcription, translation, 70S ribosome function and cell wall formation
Since viruses do not metabolize on their own (they use our cell’s metabolic machinery) they are not effected by the antibiotics

15. 6.3
Antibiotics: Types
_____-static: (bacteriostatic, fungistatic) stop further growth but don’t kill existing microbes.
Buys time for immune system to catch up and target microbes.
_____-cidal: (bacteriocidal, fungicidal) kills microbes

16. Antibiotic resistance
Some bacteria develop a gene mutation that makes them naturally resistant to antibiotics
Resistance can be transferred from strain to strain and sometimes from species to species
Bacteria that have a resistance mutation survive when antibiotics are used and other bacterium die

17. Resistant bacteria pass on their genes for resistance to offspring
Proportion of resistant bacteria increases in each generation
This is an excellent example of natural selection and evolution

18. 6.3
Antigen and Antibodies

19. 6.3 Antigen and Antibodies Antigens
Large molecules on the outer surface of cells
All living cells as well as viruses have antigens
All cells in one organism will have the same type of antigen (which is genetically controlled)
Therefore, the antigen acts as identification marker for cells
If a pathogen enters the body the immune system will detect the foreign antigen and begin to attack

20. 6.3 Antibodies (also called immunoglobulin)
Proteins that bind to the specific antigen on a pathogen to help to destroy it
Each has a variable region that is antigen specific (similar to enzyme specificity)

21. 6.3
Youtube.com Specific Immunity: Antibodies

22. 6.3 Many types of b-cells exist
Antibody production
Many types of b-cells exist
Each type recognizes one specific antigen and responds by dividing to form a clone
This clone then secretes numerous copies of a specific antibody against the antigen
Cloning and antibody production is always initiated by the binding of a t-cell (another type of white blood cell) to the b-cell

23. 6.3

24. 6.3
HIV and Aids
HIV, or Human Immunodeficiency Virus, was first noticed by the CDC (center for disease control) in 1981
The U.S. origin of the disease was traced back to “patient zero”, a french flight attendant who slept with hundreds of men throughout the country

25. 6.3 HIV and AIDS HIV can remain hidden in the body for years
It survives by invading and killing T-Cells
When enough T-cells have been destroyed, the immune system begins to fail and AIDS, or Acquired Immune Deficiency Syndrome, has begun
Aids patients do not die from the virus itself, but rather from the diseases that take hold of the body in the absence of a proper immune system
Many anti-viral drugs are now available for AIDS patients

26. Effect of HIV on Immune System
The HIV virus limits the number of active lymphocytes in an organism
This makes it much harder for the organism to fight off possible infectious pathogens
Lose the ability to produce antibodies
Leads to the development of AIDS

27. 6.3
The drugs usually do not work alone, however, and must be administered in combinations called “cocktails”
The drugs do not destroy the virus completely, but rather slow down the rate of replication
After a few years, the drugs tend to lose their affect and the patient must begin a new drug regime
Sides effects of the drugs can be horrible and include hallucinations, insomnia, and severe depression

28. 6.3
HIV is transmitted through vaginal fluid, semen, blood, and sometimes breast milk
Sexual contact and IV drug use (sharing of dirty needles) are the most common ways that these bodily fluids are passed from person to person
The social implications of AIDS are numerous and devastating, especially in southern Africa where the number of cases is disproportionate to other areas of the world

29. 6.3
As a result of the large numbers of people with the disease and no health care in these nations there are many orphaned children
Having AIDS or having family members with the disease also provides a social stigma that may make it hard to get a job
Having AIDS may also make it hard to obtain health insurance