Disease, Defense and Treatment

• Pathogen


  A microorganism that causes disease
• Non-pathogenic microorganism


  Any microorganism that does not cause disease
• Non-pathogenic microorganisms


  • Gut bacteria help to digest food
  • Skin flora help to prevent infection by competing with pathogens for resources
• Types of pathogen


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria cells


  • Cell membrane
  • Cell wall
  • Cytoplasm
  • Plasmid loops of DNA
  • No nucleus but large DNA loop instead
• Virus


  They contain some genetic material surrounded by a protein shell
• Ways diseases can be spread

  • Droplet infection
  • Eating contaminated food
  • Drinking contaminated water
  • Direct contact
  • Vectors like insects
  • Contact with infected bodily fluids
• Human immunodeficiency virus (HIV)


  The pathogen that causes AIDS
• Symptoms of AIDS


  • HIV weakens the immune system
  • Fever
  • Flu-like symptoms
  • Rash
• Preventing the spread of HIV

  1. Don't share needles

  2. Wear condoms during sex
• Chlamydia trachomatis


  The pathogen that causes chlamydia
• Symptoms of chlamydia


  • Pain when urinating
  • Painful discharge from the penis or vagina
  • Bleeding between periods for women
• Preventing the spread of chlamydia

  Wear condoms during sex
• Plasmodium falciparum


  The pathogen that causes malaria
• Symptoms of malaria


  • Fever
  • Vomiting and diarrhoea
  • Headaches
  • Muscle and/or abdominal pain
• Preventing the spread of malaria

  1. Wearing long clothing

  2. Wearing mosquito repellent

  3. Sleeping with mosquito nets

  4. Use malaria prevention tablets
• Non-specific human defences to disease

  • The skin acts as a barrier
  • Stomach acid kills ingested pathogens
  • Mucus traps pathogens
  • Sweat contains antimicrobial chemicals
  • Blood clots prevent pathogen entry into wounds
• Ways the body can respond to detecting a pathogen


  • They can produce antibodies that are specific to the antigens on the pathogen that activate phagocytes
  • They can produce antitoxins to neutralise the toxins released by the pathogen
• Phagocytosis


  The process where phagocytes engulf and break down pathogens
• Antigens


  Molecules on the surface of cells that are recognised by the immune system and trigger an immune response
• Antibodies


  Specific molecules that bind to antigens and help the immune system to neutralise the infection
• Types of pathogen that vaccines can protect against

  • Bacteria
  • Viruses
• Reasons parents might choose to have their child vaccinated

  • Vaccines save lives and will prevent their child from getting certain diseases
  • Parents in countries without free healthcare may not be able to afford treatment if their child falls ill from a disease
• Reasons parents might choose not to have their child vaccinated

  • They may be concerned about the potential side effects of vaccination
  • They may be unaware of the contents of the vaccine
  • They may have religious or cultural objections to it
  • They may believe that vaccines are linked to certain other diseases like autism, asthma and multiple sclerosis
• Not vaccinating children can lead to breakouts of diseases which may cause epidemics or pandemics and put a strain on the healthcare system
• How vaccines work (Higher)

  1. Dead or inactive pathogens or antigens for a disease are injected into the body

  2. Lymphocytes produce antibodies against the pathogen

  3. Memory cells are also created to provide long term immunity
• The secondary response to a pathogen is much faster than the initial response (Higher)
• How vaccines work

  1. Dead or inactive pathogens or antigens for a disease are injected into the body

  2. Lymphocytes produce antibodies against the pathogen

  3. Memory cells are also created to provide long term immunity
• The activation of the immune system in response to a new pathogen is relatively slow


  Memory cells that remain in the blood speed up the process and can produce many antibodies much quicker
• Antibiotics kill bacteria
• Penicillin was discovered by Alexander Fleming


  1928
• Antibiotics


  Stop bacteria from growing or kill them completely without damaging the host cells which can cure bacterial diseases
• A fungus called penicillium produces penicillin
• Semisynthetic penicillin


  Penicillin that has been modified chemically
• Synthetic penicillin

  Penicillin that has been produced from scratch chemically rather than being produced naturally by microorganisms
• MRSA (Methicillin-resistant Staphylococcus aureus) is an example of an antibiotic resistant bacterium
• Ways of controlling the spread of MRSA

  • Cover wounds with sterile dressings
  • Wash your hands, surfaces and equipment often and thoroughly
  • Treatment and screening programmes
• Ways diseases can be prevented

  • Washing hands
  • Having a balanced and healthy diet
  • Drinking clean water
• Stages in the development of new medicines

  1. Research the drug and test it on lab grown cells

  2. Test on animals

  3. Test on healthy volunteers

  4. Test on people who have the disease
• Preclinical trials


  Testing the drug on lab grown cells and tissues and using computer modelling to understand the effects of the drug