Infection and Response

• Communicable Disease


  Diseases that can easily spread
• Types of Pathogen


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Pathogens


  • Microorganisms that enter the body and cause disease
  • Can cause communicable (infectious) diseases
  • Can infect both plants and animals
• Bacteria


  Very small living cells that can reproduce rapidly inside the body and produce toxins that damage cells and tissues
• Viruses


  Not cells, much smaller than bacteria, can reproduce rapidly inside cells using the cell's machinery, then cause the cell to burst releasing new viruses
• Protists


  Single-celled eukaryotes, some are parasites that live on or inside other organisms and can be transferred by a vector
• Fungi


  • Some are single-celled, others have a body made up of hyphae that can grow and penetrate human skin and plant surfaces, producing spores that can spread
• Ways Pathogens Can Be Spread


  • Water
  • Air
  • Direct Contact
• Pathogens can have massive effects on the body, especially bacteria and viruses which can multiply extremely rapidly
• Diseases caused by viruses or fungi


  • Measles
  • HIV
  • TMV (Tobacco Mosaic Virus)
  • Rose Black Spot
• Measles


  Viral disease that causes a red skin rash and fever
• How measles spreads


  Spread by droplets from an infected person's sneeze or cough
• Measles


  • Can lead to serious complications like pneumonia or encephalitis
  • Most people are vaccinated against measles when young
• HIV


  Viral disease spread by sexual contact or sharing needles when taking drugs
• HIV infection progression


  1. Initially causes flu-like symptoms, then no symptoms for years as it can be controlled with antiretroviral drugs

  2. When immune system is badly damaged, it becomes late stage HIV infection or AIDS
• Tobacco Mosaic Virus (TMV)


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


  Fungal disease that causes purple/black spots on rose leaves, reducing photosynthesis
• How Rose Black Spot spreads

  Spreads through water or wind
• Rose Black Spot


  • Gardeners can treat it using fungicides and removing affected leaves
• Malaria


  Disease caused by a protist, spread through mosquitoes
• Malaria life cycle


  1. Part of protist's life cycle takes place inside a mosquito

  2. Mosquitoes pick up protist when feeding on infected animal

  3. Mosquito infects another animal by inserting protist into its blood vessels
• Malaria


  • Causes repeating episodes of fever, can be fatal
  • People can be protected using insecticides and mosquito nets
• Salmonella


  Bacterial disease that causes food poisoning with symptoms like fever, stomach cramps, vomiting and diarrhoea
• How Salmonella is contracted


  By eating food contaminated with Salmonella bacteria, e.g. undercooked chicken or food prepared in unhygienic conditions
• Gonorrhoea


  Sexually transmitted bacterial disease that causes pain when urinating and discharge
• Gonorrhoea treatment


  1. Originally treated with penicillin, but now strains are resistant so other antibiotics are used

  2. Prevented by using barrier contraception like condoms
• Ways to reduce or prevent disease spread


  • Being hygienic (e.g. handwashing)
  • Destroying disease vectors (e.g. killing mosquitoes)
  • Isolating infected individuals
  • Vaccination
• Vaccination can be a real life saver
• Human body's features that fight disease


  • Skin acts as barrier to pathogens & secretes antimicrobial substances
  • Hairs and mucus in nose trap particles that could contain pathogens
  • Trachea and bronchi secrete mucus to trap pathogens
  • Trachea and bronchi lined with cilia that waft mucus up to back of throat
  • Stomach produces hydrochloric acid to kill pathogens
• Non-specific defence systems


  Body's first line of defence against pathogens
• Immune system


  • White blood cells travel around and patrol for microbes
  • White blood cells can consume and digest foreign cells (phagocytosis)
  • White blood cells produce antibodies specific to foreign antigens
  • Antibodies rapidly produced to kill same pathogen if infected again
• 1. lymphocytes


  White blood cells that produce antibodies
• Vaccination


  Injecting small amounts of dead or inactive pathogens to stimulate antibody production
• Basia is vaccinated against flu and Cassian isn't


  Cassian falls ill whereas Basia doesn't
• Pros of vaccination


  • Helped control many communicable diseases
  • Can prevent epidemics if large percentage of population vaccinated
• Cons of vaccination


  • Vaccines don't always work
  • Possible bad reactions, though rare
• Painkillers


  Drugs that relieve symptoms without tackling underlying cause
• Antibiotics


  Drugs that kill or prevent growth of bacteria causing problem
• Antibiotics don't destroy viruses
• Bacteria can mutate to become resistant to antibiotics


  Resistant strains survive and reproduce, increasing in population