Defense Against Infectious Diseases

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)

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

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/DNA 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

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

Barriers to infections·First line of defense: prevent pathogens from entering the blood stream

- Skin> a tough, impenetrable physical barrier> has a lower pH which make it inhospitable

for many bacteria> Sweat has lysozymes (special enzymes)

that destroy bacteria

- 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)

nonspecific

antigen specific

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.

- Phagocytes: large, irregularly-shaped leukocyte cells that remove bacteria, viruses, cellular debris and dust particles.

> 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

Antigen and Antibodies

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

·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)

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

HIV and Aids·HIV stands for Human Immunodeficiency Virus

>can lead to AIDS (acquired immunodificiency syndrome)·It survives by invading and killing T-Cells·When enough T-cells have been destroyed, the immune system begins to fail and AIDS has begun

Treatment Research

HIV and AIDS·Aids patients do not die from the virus itself, but rather from "opportunistic infections"

>the diseases that take hold of the body in the absence of a proper immune system

Is transmitted Is Not transmitted

·Semen·Pre-ejaculate·Vaginal fluid·Blood·Shared needles

·Saliva·hand shakes·clothing·Air·Water

HIV transmission mediums

HIV Testing·find a clinichttp://hivtest.cdc.gov/·home tests

Who should get tested?·everyone between the ages of 13 and 64 at least once as part of routine health care. ·Testing once a year (or more) is recommended for people at higher risk of HIV infection

AIDS: Acquired Immuno deficiency syndrome.·Acquired relates the infectious nature of AIDS through the transmission of the HIV virus.·Immuno deficient relates to the way diseases cannot be resisted. ·Syndrome relates to the variation in the way the disease manifest itself. People who develop AIDS can be a affected by quite different set of diseases.

Cause: is the HIV retro-virus that selectively infects cells of the immune system effectively disabling primary and secondary response to infection.Transmission: Through contact with the body fluids of an infected person. In particular the fluids are blood and semen, vaginal mucus. There is a very low risk ( almost zero) associated with salivary mucus