10. Diseases and Immunity

Two main forms of transmission are identified:

  • Direct contact (e.g., chickenpox and HIV transmission).

  • Indirect contact (e.g., through contaminated surfaces, foods, or vectors like mosquitoes).

Body Defenses Against Pathogens

  • The body has several defenses against pathogens:

  • Skin acts as a physical barrier that heals to form scabs when wounded.

  • Nose hairs filter out pathogens that could enter the lungs.

  • Mucus traps pathogens; it can be removed by blowing the nose or swallowing.

  • Stomach acid, primarily composed of hydrochloric acid, kills pathogens ingested with food.

  • White blood cells, which include phagocytes and lymphocytes, play critical roles in combating infections.

Active Immunity

  • Active immunity arises from antibody production in response to infection or vaccination.

  • Pathogens have unique surface markers called antigens, which lymphocytes recognize.

  • Antibodies are proteins produced by lymphocytes that bind to specific antigens, leading to the destruction or marking of pathogens for phagocytes.

  • Memory cells created during an immune response enable rapid antibody production upon re-exposure to the same pathogen, providing long-term immunity (e.g., immunity to chickenpox).

Vaccination

  • Vaccination introduces weakened pathogens or their antigens into the body to stimulate an immune response without causing illness.

  • This process promotes the production of antibodies and memory cells, resulting in long-term immunity.

  • The effectiveness of vaccination in controlling disease spread is linked to herd immunity, where widespread vaccination reduces the transmission of pathogens.

Passive Immunity

  • Passive immunity provides short-term protection through antibodies acquired from another individual, such as a mother to her baby.

  • Antibodies can be transmitted across the placenta or via breast milk, protecting infants whose immune systems are still developing.

  • Unlike active immunity, passive immunity does not involve memory cell production, making it a temporary solution.

Cholera

  • Cholera is a bacterial disease spread through contaminated water, leading to severe diarrhea and dehydration.

  • The cholera bacterium produces a toxin that affects the intestines, causing fluid loss.

  • Treatment for cholera involves Oral Rehydration Therapy, which replenishes lost salts and sugars.