B3.1 - Communicable Diseases

• What's a pathogen?

  A micro-organism which causes infection or disease. The 4 types are bacteria, protist, fungus and virus.
• Bacteria cells

  Bacteria are 100x smaller than body cells. They can reproduce every 20 minutes. They produce toxins that cause tissue damage.
• Virus cells

  Viruses are 1000x smaller than body cells (10x than bacteria). They live and reproduce within the cell causing damage. They have no reactions to antibiotics.
• What is a vector?

  An organism that doesn't cause disease but which spreads infection by conveying pathogens (protists, bacteria, fungi, virus) from one host to another.
• What is the vector in malaria?

  The vector in malaria is the female mosquito. Only female mosquitos transmit malaria because only females suck blood for protein which they need to grow eggs, where as males suck fruit nectar.
• HIV (Virus)

  Symptoms - If untreated, can get swollen lymph nodes, weight loss, fever, infection or fatigue.

  Treatment - No cure, can be stopped from turning into aids with anti-retro viral drugs.

  Transmission - Spread through bodily fluids e.g. sharing needles or sex.

  Prevention - Not touching other's bodily fluids.
• Measles (Virus)

  Symptoms - Total body skin rash, feverish symptoms, spots in mouth.

  Treatment - No treatment. Drink lots of fluids and rest. If fever is bothering you, can take ibuprofen.

  Transmission - Spreads when infected person coughs or breathes.

  Prevention - Vaccinations
• Tobacco Mosaic Virus (TMV) (Virus) (PLANTS ONLY)

  Symptoms - Mosaic, Mottling, Necrosis, Stunting, Leaf curling, Yellowing of plant tissues

  Treatment - Fungicide spray

  Transmission - Spreads when an infected leaf rubs against a healthy one, contaminated tools are spread between leafs, and seed roots come in contact with each other.

  Prevention - Fungicides
• Rose Black Spot (Fungus) (PLANT ONLY)

  Symptoms - Purple/Black spots on leaves, leaves falling early, leaf tissue may turn yellow.

  Treatment - Fungicide spray

  Transmission - Water transmission

  Prevention - Fungicide spray
• Gonnorea (Bacteria - Neisseria)

  Symptoms - Painful urination, cloudy discharge

  Treatment - If caught early, can be treated with antibiotics

  Transmission - Spread through sexual contact or from mother to child

  Prevention - Abstaining from having sex
• Malaria (Protists)

  Symptoms - Irritability, drowsiness, poor appetite, trouble sleeping, chills, fever, intense sweating

  Treatment - Anti-malarial drugs

  Transmission - Mosquitos

  Prevention- Window screens, repellent, nets and drugs
• Salmonella (Bacteria)

  Symptoms - Nausea, vomiting, cramps, headaches, fevers, and diarrhea.

  Treatment - Antibiotics

  Transmission - Eating raw food

  Prevention - Cooking food thoroughly
• How to prevent pathogens?

  1. Washing hands with soap before touching food.
  2. Destroying vectors (No Mosquitos)
  3. Isolation
  4. Vaccinations
• Lifecycle of the plasmodium (infected mosquito)


  1. Infected mosquito bites human. The mosquito is a vector meaning it carries and transfers the pathogens.
  2. Plasmodium enters the red blood cell inside the human body.
  3. Plasmodium reproduces and causes red blood cells to burst. (goes back to step 2 and loops till it's all infected)
  4. A second mosquito bites an infected human and becomes infected (goes back to step 1 and loops)
• Body's natural defences from pathogens

  Nose hairs, Skin scabs, Top layer of skin is dead w/ Stem cells beneath, White Blood Cells

  Eye lids and lashes -> Tears with enzymes (lysosomes) that kill pathogens.

  Air ways -> Mucus membranes, goblet cells, cillia (tiny hairs) in trachea, wafts Mucus away from lungs.

  Stomach -> Hydrochloric Acid that kills pathogens.
• Roles of white blood cells

  • Releasing antitoxins to neutralise pathogen's toxins
  • Perform phagocytosis (engulf and digest pathogens)
  • Produce antibodies that destroy pathogens or make them clump together
• Why doesn't the body keep catching the same disease?

  1. White blood cells learn to recognise the shape of the antigen.
  2. They produce an antibody with a complementary shape to destroy the pathogen, called B Lymphocytes.
  3. Next time your body encounters the pathogen, it will recognise the antigen straight away, called Memory B Lymphocytes.
  4. This mean that it can produce antibodies more rapidly, and therefore destroy the pathogen quicker through phagocytosis.
• What is an antibody?

  Produced by white blood cells in the body - they destroy pathogens.
• What is an antigen?

  A protein on the surface of a pathogen.
• What is an antitoxin?

  Counteracts the toxins made by Bacteria.
• How do vaccinations prevent disease?

  1. Patient is injected with a dead/weakened/inactive strain of the pathogen.
  2. The antigens on the pathogen are detected by the white blood cells.
  3. White blood cells produce antibodies which bind to antigens on the surface of the pathogen.
  4. When the pathogen is encountered again, hite blood cells produce antibodies quicker, killing the pathogen before you get the disease.
• What is an epidemic?

  Rapid spread of infectious disease to a large number of people in one country or community.
• What is a pandemic?

  Epidemic that Spreads on a world wide scale, e.g. COVID.
• What is herd immunity?

  Where over 95% of the population is vaccinated, making it harder to spread infections. It can help to prevent epidemics and pandemics as it can stop it spreading from community to community.
• Why may some people not get immunised/vaccinated?

  2 types of people:

  1. Infants as they're to young
  2. Those who disagree due to ethical reasons
• Advantages and disadvantages of vaccinations

  A - Prevents disease and deaths, avoids treatment costs, eradication of diseases e.g. smallpox

  D - May be side effects, strains can mutate, in poor/less developed areas, can be very costly
• Why do you need to finish your entire course of antibiotics?

  Strains can mutate and become resistant if they hadn't been cured.
• Why is it difficult to develop drugs that kill viruses?

  Because the virus infects a cell and hijacks the cell's machinery in order to create more copies of itself. Destroying the virus will often mean destroying the cell that the virus is inside of.
• What are painkillers?

  Painkillers are chemicals that relieve the symptoms but do not kill the pathogens. Common examples include paracetamol and aspirin, and they can relieve a headache or a sore throat.
• What were drugs originally extracted from?

  Plants and microorganisms.

  Aspirin (Painkillers) was found from willow.

  Digitalis (Heart drugs) was found from fox gloves.

  Penicillin (Antibiotics) was found from mould by Alexander Flemming.
• What are most new drugs found from?

  Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant.
• What is toxicity?

  How harmful something is.
• What is efficiency?

  Whether the drug works and produces the effect you want.
• What is dosage?

  Volume and concentration to take of something.
• What is a placebo?

  A tablet containing no drugs given to some subjects so they can compare results?
• What is the difference between a blind trial and a double blind trial?

  Blind trial - Volunteers don't know what they're taking whereas doctors do.

  Double blind trial - Neither the volunteers nor doctors know what They're taking, only the scientists do.
• First stage of testing new drugs

  1. The drugs are tested using computer models and skin cells grown using human stem cells in the laboratory. This allows the efficacy and possible side effects to be tested. Many substances fail this first test of a preclinical drug trial because they damage cells or do not seem to work.
• Second stage of testing new drugs:

  2. Drugs that pass the first stage are tested on animals in the second part of a preclinical drug trial. In the UK, new medicines have to undergo these tests. But it is illegal to test cosmetics and tobacco products on animals. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side-effects.
• Third stage of testing new drugs:

  3. Drugs that have passed animal tests are used in human clinical trials. They are tested on healthy volunteers to check that they are safe. The substances are then tested on people with the illness to ensure that they are safe and that they work. Low doses of the drug are used initially, and if this is safe the dosage increases until the optimum dosage is identified.
• What are monoclonal antibodies

  Antibodies made in a laboratory artificially