6.3: Defense against infectious disease

A pathogen is an organism or virus that causes disease. There are different types of pathogen

1. Viruses e.g. Influenza, chicken pox, poliomyelitis

2. Bacteria Tetanus, tuberculosis

3. Fungi. Athletes foot, ringworm, thrush

4. Protozoa. Malaria, sleeping sickness

5. Flatworms Bilharzia (caused by blood fluke)

6. Roundworms Elephantiasis (blocked lymphatic system)

How does the Human body prevent pathogens from entering?

Skin as a barrier Skin and mucous membranes form the first defense against pathogens. Tough, outer layer provides a physical barrier. Sebaceous glands secrete sebum, to maintain moisture and lowers skin pH.

Goblet cells & cilia inside the trachea. Goblet cells (pink) secrete mucus (form of glycoprotein), trap incoming pathogens. Antiseptic properties due to presence of lysozyme

Blood clots ‘Seal’ damaged blood vessels – reduces blood loss and when the cut/damage occurs on the skin, prevent pathogens from entering the body.

Damaged blood vessel 1.Damaged cells in blood vessel release chemicals 2.Platelets to bind to the damaged area 3.More platelets bind to the area – form a ‘plug’ 4.Clotting factors released (from platelets) strengthen the ‘plug’ 5.More and more debris attaches to the plug until it is stable Clotting factors convert prothrombin  thrombin (enzyme) Thrombin converts soluble fibrogen  insoluble fibrin Why do this?

Coronary thrombosis The formation of blood clots in the coronary arteries. This causes part of the heart to be deprived of oxygen and nutrients  irregular contractions (decrease of aerobic respiration) known as fibrillation. Atherosclerosis causes occlusion of the coronary arteries, arterial endothelium becomes brittle (artery wall hardened by deposits of calcium salts). Atherosclerosis increases the risk of thrombosis. Risk factors include: - Smoking - High blood cholesterol concentration - High blood pressure - Diabetes - Obesity - Lack of exercise

Phagocytes Phagocytic white blood cells = cells designed to engulf and digest pathogens by endocytosis. Move to the site of infection by squeezing out of the capillaries. Pus forms as a by-product of the digestion of pathogens.

Antibody production Antibodies are produced by lymphocytes in response to pathogens. This is a specific form of immunity. Proteins on the surface of the pathogen are recognized as foreign by the body  immune response. Antibodies are produced by lymphocytes and bind to the antigen. Each type of lymphocytes produces one antibody, therefore we have many different types of lymphocytes in our bodies.

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Summary Phagocytes = non specific immunity (engulf & digest) Lymphocytes = specific immunity. Antibody producing. Plasma cell is a large clone, secrete large numbers of antibodies. Antigen = ANY chemical that causes an immune response. Antibodies = large proteins, bind to a specific antigen. Antibodies/plasma cells etc. do not persist in the body after infection. But lymphocytes can become inactive memory cells. Immunity to a disease = either having antibodies or memory cells to rapidly produce antibodies upon re-exposure.

Antibiotics take advantage of the differences between prokaryotes and eukaryotes. There are many different types of antibiotics, disrupting different biochemical reactions. E.g. protein synthesis, cell growth etc. Antibiotics have no effect on viruses. Virus use our own body cells to create new viruses. Antibiotics cannot interfere with the metabolism of eukaryotic cells, only prokaryotes. Sketch pro/eukaryote cells.

Testing of penicillin 1.September 3 rd, 1928 – Fleming made the first observations regarding penicillin 2.Chain & Florey, 1939, started work on purification & understanding the chemistry of the drug Read pages 308/8 regarding the testing of penicillin. Would this be allowed today? Discuss.

Viruses and antibiotics Viruses cannot be treated with antibiotics because they do not have a metabolism. They use enzymes in the host cell for their metabolic reactions. Antivirals are a type of drug that can disrupt the metabolism of a virus without affecting the host cell. But there are not many of these drugs at the moment! Podcast *BEWARNED, there is some bad language!* 30mins

“The danger posed by growing resistance to antibiotics should be ranked along with terrorism on a list of threats to the nation. If we don’t take action, then we may all be back in an almost 19 th century environment where infections kill us as a result of routine operations. We won’t be able to do a lot of our cancer treatments or organ transplants.” Sally Davies, Chief medical officer for England

Antibiotic resistance data: Europe esistance/database/Pages/map_reports.aspx Nice introduction e7.swf News report 7/ /as-antibiotic-resistance-spreads-who- plans-strategy-to-fight-it Video udent_view0/exercise20/cell_wall_antibiotics.html

Antibiotic resistance Some bacteria are able to become resistant to antibiotics due to evolution by natural selection. Antibiotic resistance is avoidable: 1.Antibiotics used for ONLY serious infections 2.Patients always completing course of antibiotics 3.High standards of hygiene in hospitals 4.No antibiotics in animal feed 5.Pharmaceutical companies designing new antibiotics – last new antibiotic 1980’s!

HIV - retrovirus Damages the immune system Affects the helper-T cells (communicators cell in the blood stream) Immune response is disrupted as helper-T cells begin to die, antibodies are no longer produced. Individual can no longer fight invading pathogens.