• A pathogen is a disease-carrying organism
• Transmissible disease is a disease in which the pathogen can be passed from one host to another
• The pathogen for a transmissible disease may be transmitted either through direct contact, e.g. through blood or other body fluids, or indirectly, e.g. from contaminated surfaces or food, from animals, or from the air
• The body has defenses:
  • mechanical barriers, limited to skin and hairs in the nose
  • chemical barriers, limited to mucus and stomach acid
  • cells, limited to phagocytosis and antibody production by white blood cells which can be enhanced by vaccination

Active Immunity

• Active immunity is defense against a pathogen by antibody production in the body
• Pathogens have markers on their surface membranes called antigens
• Antibodies stick to these antigens and destroy the pathogens or mark them for phagocytes to act on them
• Active immunity is gained after an infection by a pathogen, or by vaccination

Process of Vaccination

• Harmless pathogens given which have antigens
• Antigens trigger an immune response by lymphocytes which produce antibodies
• Memory cells are produces that give long-term immunity

The Role of Vaccination in Controlling the Spread of Diseases

• Vaccines immunize disease caused by pathogens
• A vaccine is a dead virus or bacteria that stimulates lymphocytes to produce antibodies and be immune to that particular disease
• The next time the disease comes, it will be destroyed before getting the change to spread

The Importance of Hygienic Food Preparation, Good Personal Hygiene, Waste Disposal, and Sewage Treatment in Controlling the Spread of Disease

• Personal Hygiene: Keeping the body clean can reduce the risk of getting or passing on transmissible diseases
• Waste Disposal: Bacteria breed in waste
• Sewage Treatment: If sewage is not treated before being run into rivers or sea, it can harm the environment and people. Treating the sewage can prevent this

Passive Immunity

• Passive immunity is short-term defense against a pathogen by antibodies acquired from another individual, e.g. mother to infant
• Memory cells are not produced in passive immunity

The Importance of Passive Immunity for Breast-fed Infants

• The immune system in a baby’s body has not been developed yet, so the mother’s antibodies can protect it against any disease she is immune to
• Some diseases are caused by the immune system targeting and destroying body cells; limited to type 1 diabetes