immunity

• Disease

  A disorder that negatively affects the structure or function of all or part of the body or the mind that leads to poor health
• Health

  A physical, mental and social well-being
• Pathogen

  A living organism that can cause disease e.g. bacteria, protoctist, fungus. Viruses are infectious particles
• Microorganism


  A living organism which is too small to be seen by the naked eye and can only be seen by a microscope. It can be harmful or beneficial to other living organisms
• Viruses


  Non-cellular, consisting of a nucleic acid (DNA or RNA) surrounded by a protein coat (capsid) formed of small units called capsomeres. They lack cell structures and metabolic machinery, do not show characteristics of living organisms, and cannot reproduce on their own. However, they can reproduce inside a host cell and cause diseases

  
• How viruses replicate


  1. Virus injects its genetic information into the host cell

  2. Controls the cell's machinery to use the cell materials and manufacture new virus nucleic acids and coats

  3. Host cell bursts open

  4. Viruses are released promoting further infection

  
• Infectious (transmissible) disease


  A disease caused by a pathogen which can be transmitted from one person to another or from an animal to a human

  
• How pathogens cause disease

  1. They damage the cells in which they live and replicate as they use the cells' resources

  2. They produce toxins that harm the different body organs and cause symptoms such as fever, cough and pain
• Noninfectious (nontransmissible) disease


  A disease that is not caused by a pathogen and cannot be transmitted from one person to another e.g. genetic diseases, nutritional diseases, degenerative diseases, autoimmune diseases, diseases due to environmental causes
• Bacterial Diseases


  • Cholera
  • Tuberculosis
  • Gonorrhoea
• Cholera

  symptoms include rice watery diarrhea, dehydration and weakness. Treated with rehydration therapy and antibiotics
• Tuberculosis


  Caused by Mycobacterium tuberculosis, symptoms include cough, coughing blood, chest pain, shortness of breath, fever and night sweating, loss of appetite and weight. Treated with a cocktail of antituberculous drugs
• Gonorrhoea, symptoms in men include pain and discharge of pus from the urethra, in females the same or symptomless. Treated with penicillin
• Influenza (flu)


  Caused by a virus, symptoms include fever, headache, dry cough, mild sore throat. No specific drugs, antibiotics may be used against secondary bacterial infection
• Measles, symptoms include fever, rash, cough, red watery eyes. No specific medicine, treated with antipyretics and bed rest
• German measles


  Caused by Rubella virus, transmitted by droplet infection or through placenta from mother to foetus leading to malformations or abortion. Symptoms include low grade fever, sore throat, rash. Treated with bed rest and medicine for fever
• Acquired Immunodeficiency Syndrome (AIDS)


  Caused by Human Immunodeficiency Virus (HIV) which attacks T-helper lymphocytes and macrophages, weakening the immune response. Symptoms include flu-like symptoms initially, then opportunistic infections, diarrhea, fever, sweating, cancer, loss of memory and coordination. No cure, Zidovudine slows disease progress

  
• Modes of HIV transmission

  • Direct infection of blood (blood transfusion, sharing contaminated needles, haemophiliacs receiving infected blood products)
  • Sexual transmission through semen and vaginal fluid
  • Mother to child (in utero, during birth, breastfeeding)
  • Tissue and organ transplantation
  • Inefficient sterilization of dialysis machine
  • Sharing contaminated personal utensils
• Diagnosis of HIV

  Blood tests detect HIV antibodies, not the virus itself. If antibodies are present, the person is HIV positive

  
• Treatment of HIV

  No cure, Zidovudine slows down disease progress but has harmful side effects
• How to avoid HIV transmission

  • Health education
  • Avoid sexual intercourse with infected person
  • Use condoms and femidoms
  • Stop sharing needles
  • Screen collected blood
  • Contact tracing
  • HIV positive females avoid having babies and breastfeeding
• Why it is difficult to control the spread of HIV: 1) Symptomless carriers can infect others, 2) No treatment, 3) Difficult to develop vaccine due to rapid mutation of HIV
• Modes of Transmission of Bacteria and Viruses

  • Direct contact (through blood or other body fluids)
  • Droplet infection or airborne infection
  • Foodborne
  • Waterborne
  • Vectors (animals or insects)

  
• Role of Natural Physical and Chemical Barriers in Preventing Entry of Microorganisms

  • Outer layer of skin epidermis
  • Acidic secretions from oil and sweat glands
  • Hairs and mucus in nasal passages
  • Mucus membranes lining tracts
  • Blood clots and scabs
  • Gastric acidity
  • Lysozyme enzyme in tears and saliva
• Composition of Blood


  Red cells, white cells and platelets floating in plasma

  
• White Blood Cells


  Larger than red cells, have a nucleus, undergo maturation and development in thymus gland, lymph nodes and spleen. Main types are phagocytes and lymphocytes

  
• Phagocytes


  Ingest and digest harmful bacteria, a nonspecific defence as it doesn't distinguish between different pathogens
• Lymphocytes


  Produce antibodies against bacterial antigens or foreign proteins, a specific defence as each type produces only one type of antibody

  
• Mechanisms of Action of Antibodies

  • Labelling the antigen
  • Agglutination
  • Antitoxins
  • Lysis
  • Immobilisation
  • Neutralization

  
• Vaccine


  A harmless form of the bacteria or viruses introduced into the body, stimulating the white blood cells to produce the correct antibody so that if the real microorganism gets in, the body is prepared to fight it
• Agglutination


  Antibodies clump the bacteria together to be easily engulfed and reduce their spread
• Antitoxins


  Antibodies neutralize the poisonous proteins (toxins) produced by bacteria
• Lysis


  Antibodies help to punch a hole in the bacterial cell wall and so bacteria burst open
• Immobilisation


  Antibodies attach to flagella of bacteria to reduce their activity and to be engulfed easily

  
• Neutralization


  Antibodies bound to antigens on the surface of a virus neutralize it by blocking its ability to bind to a host cell

  
• Antibodies are a specific defence because they distinguish between different pathogens and only the antibody which is complementary to the invading antigen is produced

  
• Vaccine

  A harmless form of the bacteria or viruses introduced into the body
• Types of vaccines


  • Live attenuated vaccine
  • Harmless form of the microorganism
  • Inactivated vaccine
  • Toxoid
  • Extracted antigen from the pathogen
• Active immunity


  Immunity acquired as a result of catching a disease or receiving a vaccine, where the person produces their own antibodies

  
• Artificial acquired immunity


  Immunity produced by a vaccine