infection and response

• Pathogen

  A microorganism that causes disease
• Examples of pathogens


  • Viruses
  • Bacteria
  • Protists
  • Fungi
• Communicable disease


  Infectious disease that can be spread easily
• How pathogens are spread

  1. By air (droplet infection)

  2. Direct contact

  3. Contaminated food and drink

  4. Break in the skin
• Ignaz Semmelweis


  • Noticed medical students went from dissecting dead bodies to delivering babies without washing hands
  • Insisted on hand washing before delivering babies
  • Fewer mothers died from fever
• Hygiene practices to prevent spread of disease

  • Handwashing
  • Using disinfectants
  • Keeping raw meat away from uncooked food
  • Coughing/sneezing into handkerchief
• Isolating infected individuals


  Reduces likelihood of pathogen being passed on
• Destroying vectors


  Prevents spread of disease
• Vaccination


  Injecting small amount of dead/inactive pathogen to stimulate antibody production
• How pathogens cause disease

  1. Bacteria divide rapidly and produce toxins

  2. Viruses enter body cells, reproduce and destroy them
• Measles is a viral disease with symptoms of fever and red skin rash
• Measles can be fatal if complications arise
• Measles virus is spread by inhalation of droplets from sneezes and coughs
• There is no treatment for measles, infected individuals should be isolated
• HIV initially causes flu-like illness, attacks white blood cells and compromises immune system
• HIV is spread by sexual contact, blood exchange, and unscreened blood transfusions
• There is no cure or vaccination for HIV, but antiretroviral drugs can improve long-term survival
• Tobacco Mosaic Virus causes mosaic pattern on leaves, affecting plant growth
• Insects act as vectors spreading Tobacco Mosaic Virus, there is no treatment but resistant crops can be grown
• Salmonella food poisoning is caused by bacteria ingested in food, symptoms include fever, cramps, vomiting, diarrhoea
• To prevent Salmonella, keep raw chicken away from uncooked food, avoid washing raw chicken, wash hands and surfaces well, cook chicken thoroughly
• Gonorrhoea is a sexually transmitted bacterial disease, can cause infertility and long-term pelvic pain
• Gonorrhoea can be treated with antibiotics or prevented with barrier contraception
• Athlete's foot is a relatively minor fungal skin infection, usually treated effectively with antifungal drugs
• Rose black spot is a fungal disease affecting leaves, reducing photosynthesis, spread by water or wind, can be treated with fungicides
• Protist disease


  Diseases caused by protists usually involve a vector that transfers the protist to the host
• Malaria is a serious protist disease spread by female mosquitoes, causes recurrent fever and can be fatal if not treated quickly
• Methods to control spread of malaria

  • Preventing mosquito breeding
  • Using insecticides to kill mosquitoes
  • Using insecticide-treated mosquito nets
  • Taking antimalarial drugs
• Human non-specific defence systems

  • Skin as barrier
  • Nose and respiratory system trapping pathogens
  • Stomach acid destroying pathogens
• Phagocytes


  White blood cells that ingest and destroy pathogens
• Lymphocytes


  White blood cells that produce antibodies specific to pathogens
• Antitoxins


  White blood cells that counteract toxins produced by bacteria
• Antigen


  Unique protein on the surface of each pathogen
• Antibody


  Produced by lymphocytes, specific to a particular antigen and pathogen
• How vaccination works


  1. Injecting small amount of dead/inactive pathogen

  2. Antigens stimulate white blood cells to produce specific antibodies

  3. Memory cells remember antigen shape

  4. Rapid antibody production when exposed to live pathogen
• Herd immunity


  When a large proportion of a population is immune to a disease, the spread of the pathogen is greatly reduced
• Antibiotics


  Medicines that help cure bacterial disease by killing infective bacteria inside the body
• Painkillers


  Medicines that relieve pain but do not cure the underlying disease
• Vaccine


  A small amount of dead or inactive pathogen injected into the blood. The dead pathogens have antigens on the surface which stimulate the white blood cells to produce specific antibodies to destroy the pathogens.
• Memory cells


  • Special white blood cells that remember the shape of the antigen on the pathogen