Diseases and immunity

• Pathogens


  Disease-causing organisms including viruses, certain bacteria, fungi, protoctista, and parasitic worms
• Transmissible disease


  A disease in which the pathogen can be passed on from one host to another either by direct or indirect contact
• Direct contact


  Transfer of pathogens through blood or other bodily fluids
• Indirect contact


  Transmission of pathogens via contaminated surfaces, food, animals, and particles in the air
• Examples of indirect contact transmission


  • Raw meat harboring bacteria
  • Bacteria transferred from meat to food preparation surfaces
  • Pathogens in sneezes, coughs, and breath
• Body's defense mechanisms


  • Skin
  • Mucus
  • Stomach acid
  • White blood cells
• Gastric juice


  Contains hydrochloric acid which kills majority of ingested bacteria
• Epidermis


  Outer layer of skin that acts as a physical barrier preventing pathogens from entering
• Nasal hairs and mucus in trachea/bronchi


  Filter out bacteria and foreign particles, trap pathogens
• White blood cells


  Attack pathogens that found their way into the blood and tissues
• Control measures to limit disease spread


  • Clean water supply
  • Hygienic food preparation
  • Good personal hygiene
  • Waste disposal
  • Sewage treatment
• Water treatment


  1. Filtration to remove larger particles

  2. Chlorination to kill pathogens
• Boiling water kills bacteria, viruses, and other pathogens
• Thoroughly cooking meat, consuming pasteurized milk/eggs, and washing hands regularly prevents food poisoning
• Warming up previously cooked food may cause bacteria proliferation
• Proper waste storage and disposal prevents transfer of pathogens by flies and vermin
• Sewage must be treated before release into rivers to prevent harmful bacteria from entering water supply
• Active immunity


  Defense against a pathogen by antibody production in the body
• Antibodies


  Produced by lymphocytes, bind to pathogen antigens to destroy or mark them for phagocytes
• Memory cells


  Lymphocytes that stay in lymph nodes and quickly produce more antibodies upon re-exposure to the same antigen
• Vaccination


  Introducing weakened pathogens or their antigens to stimulate an immune response and create memory cells
• Passive immunity


  Short-term defense against a pathogen by antibodies acquired from another individual, such as from mother to newborn
• Cholera


  A disease caused by a bacterium that is transmitted in contaminated water, resulting in severe diarrhea, dehydration, and potential kidney failure
• Treatment of cholera involves intravenous rehydration, salt replacement, and antibiotics to kill the bacteria