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Disease Classification


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Disease Classification

  1. 1. Learning Goals: To be able to differentiate between different types of diseases. To understand important aspects of bacteria. To be able to classify bacteria based on shape.
  2. 2. Causes of disease can be grouped into 2 main categories: 1. Congenital diseases: inherited and passed down from parent to offspring. Verne Troyer has Achondroplasia 2. Acquired diseases –contracted at some stage over a lifetime - can be subdivided into 2 types: a. Lifestyle diseases - caused by an unhealthy lifestyle e.g. heart disease; type 2 diabetes. b. Infectious disease – disease caused by a pathogen.
  3. 3. • One of the main causes of disease in an organism is the presence of another organism in or on it. Such an invading organism is called a parasite. • The organism that they ‘feed’ on is called the host. • If a parasite causes a disease state (i.e. if it makes the host sick in any way) it is said to be a pathogen. • Pathology is the branch of science involved in the study of disease and diseased tissue.
  4. 4. Pathogens may be a microorganism such as bacteria, viruses, fungi or prion; or may be a multicellular organism such as worms. Bacteria Most pathogens, and their associated infectious disease, can be transmitted from person to person (i.e. are contagious). Many infectious diseases result in death. T4 Bacteria Prions Candida albicans
  5. 5. Classification of diseases • Traumatic illnesses are injuries, • Inflammatory diseases cause fever and swelling, Hand with gout • Neoplastic conditions involve tumours or cancerous growths. • Malignant cancers are those that spread active cancer cells throughout the body, Tumour on the palate
  6. 6. • Benign cancers are those where cancer cells form tumours at one site. • Acute relates to a short, sudden episode of disease, • Chronic relates to a continuing occurrence of the disease.
  7. 7. Infectious diseases - Pathogens 1. Bacteria Bacteria are unicellular, prokaryotic organisms. Pond Bacteria Bacteria are found everywhere and only a few cause diseases. Most bacteria are saprophytes – they obtain their nutrients from dead and decaying organisms. In humans, bacteria live in the intestine and help break down food. Bacteria sample from the human tongue
  8. 8. • Bacteria vary greatly in size and morphology (shape). • Bacteria are generally between 1/1000 and 1/20 of a mm in length.
  9. 9. Bacteria Photo No. A B C D E F G H I J Bacteria Shape (baccilus, spirochaete, coccus, staphylococcus, streptococcus, diplococcus) Special features (flagella, capsule)
  10. 10. Baccilus Anthrax is the bacteria involved in the infection commonly known as anthrax. It affects the function of the lungs, the digestive system and the skin of mammals A
  11. 11. D Borellia bergdorferi is a spirochete bacteria responsible for Lyme disease. Although the first symptom of a rash seems minor, the disease can result in damage to the heart, nerves, brain, and facial paralysis. Ticks are the vector of spread for this bacteria
  12. 12. Escherichia coli is a baccilis normally found in the intestines of mammals. Some strains are responsible for causing food poisoning, and the reason for mass recall of some food products. E
  13. 13. F Neisseria meningitides is a coccus bacteria responsible for meningitis; inflammation of the protective membrane of the brain.
  14. 14. Yersinia pestis is a cocco-baccillus bacteria which was responsible for Black Death which was responsible for loss of at least 1/3rd of the population of Europe between 1347 and 1353.
  15. 15. Classifying bacteria on oxygen requirement • Bacteria that need oxygen for their survival are called aerobic bacteria. • Bacteria that do not require oxygen for survival are called anaerobic bacteria. • Facultative anaerobes can survive wether in oxygen or not. • Obligate anaerobes grow and reproduce only in the absence of oxygen.
  16. 16. Group Characteristic Examples and the disease they cause Aerobes Grow in presence of oxygen Pseudomonas aeruginosa – external ear infection Facultative anaerobes Grow wether oxygen is present or not Streptococcus pyogenes – tonsillitis Obligate anaerobes Grow only in absence of oxygen Clostridium botulinum – botulism C. tetani – tetanus C. perfringens - gangrene
  17. 17. Gram Positive and Gram Negative bacteria: • Bacteria are grouped as ‘Gram Positive’ bacteria and ‘Gram Negative’ bacteria, which is based on the results of Gram Staining Method, in which an agent is used to bind to the cell wall of the bacteria. Gram-positive bacteria take up the violet colour of the stain, Gram-negative bacteria stain pink. • Some bacteria have a special polysaccharide called teichoic acid in their cell walls, and are susceptible to penicillin and sulfonamide drugs.
  18. 18. Teichoic acid Lipid compounds Disaccharide and amino acid Disaccharide and amino acid Cell membrane Cell membrane The chemical components of the cell wall of Grampositive and gram-negative bacterium
  19. 19. • The outer layer of lipid compounds in gram-negative bacteria enables the bacteria to resist drugs. • It also makes phagocytosis of the bacteria very difficult. • Other drugs are effective against these types of bacteria. Classification based on nutritional patterns This is one of the most important classification types as it takes into account the most important aspect of bacteria growth and reproduction.
  20. 20. • Some bacteria are photosynthetic (autotrophs) use light as their energy source. • Only some of these bacteria are able to use CO2 as their carbon source. • Chemosynthetic organisms obtain their energy from oxidation reactions. • Some of these can only oxidise organic compounds for their carbon source. Others can oxidise inorganic substances such as ammonia, sulfides and iron compounds. Other heterotrophic bacteria obtain carbon and/or sugar from the the living cells or organism they are in). copy fig 7.8 p.193
  21. 21. Classification based on Phyla: • Based on the morphology, DNA sequencing, conditions required and biochemistry, scientists have classified bacteria into phyla. • Each phylum further corresponds to number of species and genera of bacteria. • The bacteria classification includes classification based on the habitat of the bacteria.
  22. 22. How do bacteria cause disease? • Bacteria can cause disease in humans if: 1. They can enter a person who acts as a host 2. They can reproduce in the host 3. They act adversely on the tissue of the host. Task: List several ways in which bacteria can be transmitted to a person.
  23. 23. Transmission to a host • Transmission of bacteria (and other pathogens) occurs by: a) From one person to another through droplets if an infected person coughs, sneezes or comes into body contact b) Contaminated water and food c) Carried from one host to another by a vector (an animal host such as a mosquito, rat or fly) A carrier of a disease is someone who has the disease, be shows no symptoms, so passes it on to others unaware of doing so.
  24. 24. Reproduction of bacteria • In order to reproduce, bacteria need an environment with adequate nutrients and water, and an appropriate temperature and pH. • When conditions are favourable, bacteria reproduce very quickly, about every 20 minutes or so. Task: Q2 p.220
  25. 25. Bacteria effects on tissues Bacteria can damage the host in several ways: 1. By producing enzymes that break down or digest tissues. 2. By producing poisonous toxins. a) Exotoxins are released into the surroundings by bacteria as they grow. Exotoxins are some of the most lethal substances known, and can (i) inhibit protein synthesis; (ii) Damage cell membranes or disrupt transport of materials across cell membranes; or (iii) Interfere with normal nerve function. Toxins retains their destructive powers after the bacteria dies.
  26. 26. b) Endotoxins are derived from the lipopolysaccharide layer in the cell wall of Gram-negative bacteria and are released after the cell lyses (breaks open). Endotoxins resist the body’s defence system better than exotoxins. Task: copy table 7.2 p.198
  27. 27. Treatment of bacterial diseases • Chemotherapy is the term used when a disease is treated with chemicals. • Many chemicals are produced, or have been extracted from bacteria and fungi to fight disease-causing agents. • Naturally occurring compounds which kill bacteria are called antibiotics. • Some drugs are narrow-spectrum and act against a limited variety or microorganisms. • Other drugs are broad-spectrum and act against many different kinds of pathogens.
  28. 28. • Broad-spectrum antibiotics are useful when the doctor is not sure which bacterium is causing an infection. • Sensitivity tests are carried out to determine which drug is most effective against the infecting bacteria. • A drug should be selectively toxic – it should kill the infecting cells without destroying the host cells. • Some drugs have adverse effects (side effects) on a host. Task: Copy table 7.3 p.200