7 - Infection & disease


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7 - Infection & disease

  1. 2. Disease <ul><li>Changes the function of an individual in some way </li></ul><ul><li>Genetic – passed on by one or both parents </li></ul><ul><li>Nutritional deficiency – lacking particular vitamin / mineral </li></ul><ul><li>Infectious – caused by pathogen </li></ul><ul><ul><li>Non cellular agent (virus / prion) </li></ul></ul><ul><ul><li>Unicellular agent (microorganism- fungi/bacteria) </li></ul></ul><ul><ul><li>Multicellular agent (worm / arthropod) </li></ul></ul>
  2. 3. Some terminology <ul><li>Infection = pathogen in host </li></ul><ul><li>Not all infections cause harm to host </li></ul><ul><li>Pathogenic = infection is causing harm </li></ul><ul><li>Epidemic – large number of infections in a short space of time </li></ul><ul><li>Pandemic – widespread outbreak of infections in a short space of time </li></ul>
  3. 4. A timeline of infectious brain diseases <ul><li>1920-21 CJD (Creutzfeld-Jacob Disease) described (Germany) </li></ul><ul><li>1957 Kuru discovered (Papua New Guinea) </li></ul><ul><li>1960s CJD contracted from hHG (human Growth Hormone) </li></ul><ul><li>1985 Scrapie in sheep discovered to be transferrable to cows </li></ul><ul><li>1987 BSE (Mad Cow Disease) discovered </li></ul><ul><li>1993 Two English farmers die of suspected CJD </li></ul><ul><li>1996 BSE identified as being transferrable from cows to humans </li></ul>
  4. 5. Prions <ul><li>Identified as the causative agents of CJD, Kuru & BSE </li></ul><ul><li>Are essentially abnormal or defective proteins </li></ul><ul><li>Cannot be killed like a virus, can only be denatured in the way that a protein would </li></ul><ul><li>Prion diseases are untreatable, only way to destroy a prion is to autoclave at a temp. of 134°C at a pressure of 138 Kpa </li></ul>
  5. 6. Prions <ul><li>Contact between our own nerve cells and an existing prion will enable replication </li></ul>
  6. 7. Viruses <ul><li>Obligate intracellular parasites – this means that they must infect a host cell in order to be able to reproduce. </li></ul><ul><li>Have DNA / RNA but no ribosomes </li></ul><ul><li>Can infect any type of organism including bacteria (bacteriophages) </li></ul><ul><li>Viruses are usually host specific </li></ul><ul><li>eg.s of diseases: common cold, influenza, poliomyelitis, measels, chickenpox, AIDS </li></ul>
  7. 8. Classifying Viruses <ul><li>Classification based on: </li></ul><ul><ul><li>Shape, symmetry & no. of protein coats </li></ul></ul><ul><ul><li>DNA or RNA </li></ul></ul><ul><ul><li>Host cell, ie specific species of: </li></ul></ul><ul><ul><ul><li>Animal </li></ul></ul></ul><ul><ul><ul><li>Plants </li></ul></ul></ul><ul><ul><ul><li>Fungus </li></ul></ul></ul><ul><ul><ul><li>Bacteria </li></ul></ul></ul>
  8. 9. Reproductive Cycle of Bacteriophages and Other Viruses
  9. 10. Reproductive Cycle of Other Types of Viruses
  10. 11. Infection of Humans by Viruses <ul><li>Some reproduce like bacteriophages & others reproduce like the poliovirus </li></ul><ul><li>Can be acute (rapid reproduction & cell death) </li></ul><ul><li>Can be chronic (slower reproduction & cell death </li></ul><ul><li>Can lay dormant for some time before activating and causing disease </li></ul><ul><li>Why do some stay in the cyctosol whilst others infiltrated the nucleus? </li></ul><ul><ul><li>Retrovirus – overtake host DNA in nucleus </li></ul></ul><ul><ul><li>Adenovirus – utilizes cell machinery to replicate </li></ul></ul>
  11. 12. Diseases Caused by Viruses <ul><li>Rubella (German Measles) </li></ul><ul><ul><li>Causes a mild fever </li></ul></ul><ul><ul><li>Can create serious complications to pregnancy </li></ul></ul><ul><ul><li>Transmitted through bodily secretions </li></ul></ul><ul><li>Polio (Poliomyelitis) </li></ul><ul><ul><li>Kills motor neurones </li></ul></ul><ul><ul><li>Results in muscle wasting and paralysis </li></ul></ul><ul><ul><li>Transmitted through contaminated food & water </li></ul></ul>
  12. 13. Influenza <ul><li>Haemogglutinin facilitates entry of virus in to cell </li></ul><ul><li>Neuraminidase facilitates exit of release of reproduced viruses from cell </li></ul>
  13. 14. Antiviral Drugs <ul><li>Difficult to develop a drug that will only target the virus and not the host </li></ul><ul><li>One strategy is to target the enzymes required by viruses – in this case, treatment will be applied locally rather than via bloodstream </li></ul><ul><li>Another strategy is to inhibit the DNA or protein synthesis of the virus </li></ul><ul><li>Relenza – blocked the active site of Neuraminidase (see previous slide) </li></ul>
  14. 15. Plant Viruses <ul><li>Some leaves are naturally variegated </li></ul><ul><li>In other cases viruses cause discoloration. Resulting in reduced photosynthesis and stunting of growth </li></ul>
  15. 16. Viroids <ul><li>Very little is known </li></ul><ul><li>Only appear to occur in plants </li></ul><ul><li>Small fragments of naked RNA that infiltrate the host cell </li></ul><ul><li>Smallest known infectious agent </li></ul>
  16. 17. Bacteria <ul><li>Prokaryotes with 1 circular chromosome </li></ul><ul><li>This chapter focuses on disease causing pathogens but most bacteria are essential for life on earth (decomposition and recycling of matter </li></ul><ul><li>eg.s of bacterial diseases: </li></ul><ul><ul><li>Diptheria, food poisoning, wound infections, tetanus, pneumonia </li></ul></ul>
  17. 18. Classification of Bacteria <ul><li>Shape and arrangement </li></ul><ul><ul><li>Round (coccus) </li></ul></ul><ul><ul><li>Rod-shaped (bacillus) </li></ul></ul><ul><ul><li>spirochaete </li></ul></ul><ul><li>Structure </li></ul><ul><ul><li>Flagella (appendage that provides mobility) </li></ul></ul><ul><ul><li>Capsule (slimy outer covering – makes more virulent) </li></ul></ul><ul><ul><li>Spore (prevents desiccation in dry environment) </li></ul></ul><ul><ul><li>Cell wall (firm, flexible layer – maintains shape) </li></ul></ul><ul><li>Reaction to stains </li></ul><ul><ul><li>Gram positive (stains violet, susceptible to penicillin) </li></ul></ul><ul><ul><li>Gram negative (stains pink, not susceptible to penicillin) </li></ul></ul>
  18. 19. Gram Positive and Gram Negative Bacteria
  19. 20. Metabolic Characteristics of Bacteria
  20. 21. Metabolic Characteristics of Bacteria <ul><li>eg. Clostridium tetani – obligate anaerobe </li></ul><ul><ul><li>Humans contact it in soil & rust all the time </li></ul></ul><ul><ul><li>If penetrates skin, deep into oxygen poor environment will cause the disease tetanus </li></ul></ul><ul><ul><li>Lock-jaw & death via respiratory spasms </li></ul></ul><ul><li>eg. C. botulinum – obligate anaerobe </li></ul><ul><ul><li>If canned foods not sufficiently heated will multiply in oxygen-poor environment and cause botulism </li></ul></ul>
  21. 22. Nutritional patterns
  22. 23. How do bacteria cause disease? <ul><li>Enter host </li></ul><ul><li>Able to grow / reproduce in host </li></ul><ul><li>Act adversely on host </li></ul>
  23. 25. Transmission to a host <ul><li>Body contact </li></ul><ul><li>Sexual contact </li></ul><ul><li>Food and water </li></ul><ul><li>Droplet or airborne </li></ul><ul><li>Carrying vector </li></ul><ul><li>Injecting vector </li></ul>
  24. 26. Bacterial Reproduction <ul><li>With correct temperature & pH as well as sufficient food and space can reproduce every 20 minutes (0 mins = 1 ) </li></ul><ul><li>After 1 hour </li></ul><ul><li>After 3 hours </li></ul><ul><li>After 6 hours </li></ul><ul><li>After 9 hours </li></ul><ul><li>After 2 days </li></ul>8 512 262,144 134,217,728 4000 x the mass of the earth
  25. 27. Effects on Tissue <ul><li>Impede blood supply </li></ul><ul><ul><li>Leads to gangrene </li></ul></ul><ul><li>Excrete collagenase </li></ul><ul><ul><li>Breaks down collagen </li></ul></ul><ul><li>Secrete exotoxins </li></ul><ul><ul><li>persist after death of bacteria </li></ul></ul><ul><ul><li>Inhibit protein synthesis </li></ul></ul><ul><ul><li>Inhibit membrane function </li></ul></ul><ul><ul><li>Interfere with nerve function </li></ul></ul><ul><li>Secrete endotoxins </li></ul><ul><ul><li>Contained within cell wall of Gram negative bacteria </li></ul></ul><ul><ul><li>More resistant to immune response </li></ul></ul>
  26. 28. Bacterial Diseases
  27. 29. Treatment of Bacterial Diseases <ul><li>Chemotherapy – treat with chemicals </li></ul><ul><li>Antibiotics – use naturally occurring substances extracted from bacteria or fungi </li></ul><ul><ul><li>Narrow spectrum </li></ul></ul><ul><ul><li>Broad spectrum (eg Penicillin) </li></ul></ul><ul><li>Ideal drug affects parasite, not host = selectively toxic </li></ul><ul><li>Adverse effect on host = side effect </li></ul><ul><li>Penicillin works by inhibiting cell wall synthesis, how does this help? </li></ul><ul><ul><li>Bacteria cannot reproduce </li></ul></ul><ul><ul><li>Animal cells don’t have a cell wall (no effect) </li></ul></ul>
  28. 30. Detecting Bacteria <ul><li>Bacterial Sensitivity Test </li></ul><ul><ul><li>Growing & plating culture take several days </li></ul></ul><ul><li>Laser light Scattering Technique </li></ul><ul><ul><li>Takes 3 hours </li></ul></ul><ul><li>Current research is in to DNA analysis </li></ul>
  29. 31. Bacteria & Plants <ul><li>Very few bacteria infect plants, far less than viruses & fungi </li></ul><ul><ul><li>Possibly because bacteria generally like an alkaline environment and the intracellular environment of plants is usually acidic </li></ul></ul><ul><li>The few bacterial plant pathogens are all rod-shaped (some have spores) </li></ul>
  30. 32. Eukaryotic Pathogens – single celled <ul><li>Amoeba </li></ul><ul><ul><li>N. fowleri causes meningitis (infects brain & spinal chord) </li></ul></ul><ul><ul><li>E. histolytica causes amoebic dysentery (traveller’s diarrhea) </li></ul></ul>
  31. 33. Eukaryotic Pathogens – single celled <ul><li>Giardia </li></ul><ul><ul><li>4 pairs of flagella (mobile) </li></ul></ul><ul><ul><li>Can be harmless until pH change </li></ul></ul><ul><ul><li>Produce toxins </li></ul></ul><ul><ul><li>Abdominal pain, diarrhea, weight loss </li></ul></ul><ul><li>Malaria </li></ul><ul><ul><li>Refer to chapter 4 for details </li></ul></ul>
  32. 34. Eukaryotic Pathogens - multicellular <ul><li>Ticks </li></ul><ul><ul><li>eg. B. bovis causes tick bite fever in cattle </li></ul></ul><ul><li>Fungi </li></ul><ul><ul><li>Absorb nutrients from substrate </li></ul></ul><ul><ul><li>Most infection superficial (skin, nails, hair) </li></ul></ul><ul><ul><li>Can enter body if immuno-compromised </li></ul></ul><ul><ul><li>Common in plants </li></ul></ul><ul><li>Arthropods </li></ul><ul><ul><li>eg. head lice, genital crabs, flys and mosquitos </li></ul></ul><ul><li>Worms </li></ul><ul><ul><li>Tapeworms </li></ul></ul><ul><ul><li>Roundworms </li></ul></ul><ul><ul><li>Nematode worms </li></ul></ul>Next
  33. 35. Life cycle of a B. bovis tick
  34. 36. Fungi <ul><li>Superficial (eg. Tinea) </li></ul><ul><li>Can be more serious </li></ul><ul><ul><li>The fungus Aspergillus flavus produces aflatoxin </li></ul></ul><ul><ul><li>Clinical trials have shown that this toxin produces abnormally high incidences of animals that ingest it. </li></ul></ul>
  35. 37. Fungi in Plants <ul><li>Can have a significant impact on people </li></ul><ul><ul><li>Irish potato famine caused the death of one million people and the emigration of two million people. </li></ul></ul><ul><li>Diagram shows the life cycle of powdery mildew on grapes </li></ul>
  36. 38. Hydatid (tapeworm)
  37. 39. Worms <ul><li>Roundworms </li></ul><ul><ul><li>Live in small intestine </li></ul></ul><ul><ul><li>Migrate to anus to lay eggs on mist skin </li></ul></ul><ul><ul><li>Life cycle able to continue when transferred back to mouth via hand, clothes or both. </li></ul></ul><ul><li>Nematode worms </li></ul><ul><ul><li>Frequently found in plants </li></ul></ul><ul><ul><li>Damage plants by secreting toxins / enzymes to brek down cells </li></ul></ul><ul><ul><li>Consume broken down cell material </li></ul></ul>
  38. 40. Sexually Transmitted Disease <ul><li>Unlike other diseases in humans which are declining, STDs are on the rise. </li></ul><ul><li>In western countries most common in people aged 15 to 30 </li></ul><ul><li>eg. genital herpes </li></ul>
  39. 41. A summary of common STDs
  40. 42. Homework <ul><li>Chapter review questions – 3 & 6-11 </li></ul><ul><li>Biozones – </li></ul><ul><li>Anatidaephobia: </li></ul><ul><li>The fear that </li></ul><ul><li>somewhere, </li></ul><ul><li>somehow, </li></ul><ul><li>a duck is </li></ul><ul><li>watching you </li></ul>