Defense Against Infectious Diseases 6.3

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

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)

The Common Cold

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

6.3 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

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.

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)

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

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.

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

6.3

https://www.youtube.com/watch?v=CEOV-SFTlpY

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

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

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

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

6.3 Antigen and Antibodies

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

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)

6.3 Youtube.com Specific Immunity: Antibodies https://www.youtube.com/watch?v=Ys_V6FcYD5I

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

6.3

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

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

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

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

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

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