B3 Infection and Response

• Communicable Disease


  Infectious diseases that can spread
• Types of Pathogen


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  • Very small living cells
  • Can reproduce rapidly inside your body
  • Can produce toxins that damage cells and cause illness
• Viruses


  • Not cells, much smaller than bacteria
  • Can reproduce rapidly inside your body
  • Live inside cells and use cell machinery to replicate
  • Can damage and burst cells
• Protists


  • Single-celled eukaryotes
  • Some are parasites that can cause damage to organisms
• Fungi


  • Can be single-celled or have a body made of hyphae
  • Hyphae can grow and penetrate human skin and plant surfaces, causing disease
  • Can produce spores that can spread to other plants and animals
• Ways Pathogens Can Spread

  • Water
  • Air
  • Direct Contact
• How Viruses Cause Cell Damage

  1. Viruses live inside cells and replicate using the cell machinery

  2. The cell then bursts, releasing new viruses
• Viral, Fungal and Protist Diseases
• Measles


  • Viral disease spread by droplets from infected person's sneeze or cough
  • Causes red skin rash and fever
  • Can lead to serious complications like pneumonia or encephalitis
• HIV


  • Virus spread by sexual contact or sharing bodily fluids
  • Initially causes flu-like symptoms, then no symptoms for years as it attacks immune cells
  • If immune system is badly damaged, leads to AIDS
• Tobacco Mosaic Virus (TMV)


  • Virus that affects many plant species
  • Causes mosaic pattern on leaves, reducing photosynthesis and plant growth
• Rose Black Spot


  • Fungus that causes purple/black spots on rose leaves
  • Reduces photosynthesis so plant doesn't grow well
  • Spreads through water and wind
  • Can be treated with fungicides and removing affected leaves
• Malaria


  • Caused by a protist
  • Part of life cycle takes place in mosquitoes, which act as vectors
  • Causes recurring fever episodes, can be fatal
  • Spread can be reduced by stopping mosquito breeding and using insecticides/nets
• Salmonella


  • Bacteria that causes food poisoning
  • Produces toxins that cause fever, stomach cramps, vomiting and diarrhoea
  • Spread by eating contaminated food, often poultry
  • Poultry is vaccinated to control spread
• Gonorrhoea


  • Sexually transmitted bacterial disease
  • Causes pain when urinating and discharge
  • Originally treated with penicillin, but now strains are resistant
  • Spread can be prevented by treatment with antibiotics and using barrier contraception
• Ways to Reduce/Prevent Disease Spread

  • Being hygienic
  • Destroying vectors
  • Isolating infected individuals
  • Vaccination
• The human body has features that stop pathogens getting in, like skin, mucus, cilia and stomach acid
• How the Immune System Attacks Pathogens

  1. White blood cells can consume and digest pathogens (phagocytosis)

  2. White blood cells can produce antibodies specific to pathogen antigens

  3. White blood cells can produce antitoxins to counteract pathogen toxins
• Vaccination has changed how we fight disease, allowing us to become immune to pathogens without getting ill
• Antigens


  Invading cells that the white blood cells don't recognise
• Immune response to antigens


  1. White blood cells produce antibodies

  2. Antibodies lock onto and destroy the invading cells
• Antibodies produced are specific to the type of antigen
• Antibody production


  1. Antibodies produced rapidly

  2. Carried around body to find all similar bacteria or viruses
• Natural immunity


  If infected with the same pathogen again, white blood cells rapidly produce antibodies to kill it
• 1. lymphocytes


  White blood cells that produce antibodies
• Producing antitoxins


  Counteract toxins produced by invading bacteria
• Vaccination involves injecting small amounts of dead or inactive pathogens
• Vaccines cause the body to produce antibodies to attack the pathogens, even though the pathogen is harmless
• How vaccines work


  1. Weakened pathogens injected

  2. White blood cells recognise and attack them

  3. Produce antibodies to kill off the pathogen
• Pros of vaccination


  • Helped control many communicable diseases
  • Prevents disease outbreaks if large percentage of population vaccinated
• Cons of vaccination


  • Vaccines don't always work
  • Possible bad reactions to vaccines
• Prevention is better than cure
• Painkillers


  Drugs that relieve pain but don't tackle the cause of the disease
• Antibiotics


  Drugs that kill or prevent the growth of bacteria causing the problem, without killing body cells
• Antibiotics don't destroy viruses
• Use of antibiotics has greatly reduced deaths from communicable diseases caused by bacteria
• Bacteria becoming resistant to antibiotics

  1. Bacteria mutate

  2. Some become resistant to antibiotics

  3. Resistant strains survive and reproduce

  4. Resistant strain causes serious infection
• To slow development of resistant strains, doctors should avoid over-prescribing antibiotics
• Patients should finish the whole course of antibiotics