Topic 3-infection and response

• Pathogens are microorganisms that enter the body and cause disease
• Types of pathogen


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  • Very small living cells (about 1/100th the size of your body cells)
  • Can reproduce rapidly inside your body
  • Can make you feel ill by producing toxins (poisons) that damage your cells and tissues
• Viruses


  • Not cells, they're tiny (about 1/100th the size of a bacterium)
  • Can reproduce rapidly inside your body
  • Live inside your cells and replicate themselves using the cells' machinery to produce many copies of themselves
  • Cell damage is what makes you feel ill
• Protists


  • Single-celled eukaryotes
  • Some are parasites that live on or inside other organisms and can cause them damage
  • Often transferred to the organism by a vector, which doesn't get the disease itself
• Fungi


  • Some are single-celled, others have a body made up of hyphae (thread-like structures)
  • Hyphae can grow and penetrate human skin and the surface of plants, causing diseases
  • Hyphae can produce spores, which can be spread to other plants and animals
• Ways pathogens can be spread


  • Water
  • Air
  • Direct contact
• Measles


  • Viral disease spread by droplets from an infected person's sneeze or cough
  • Causes a red skin rash and fever
  • Can lead to serious complications like pneumonia or encephalitis
• HIV


  • Virus spread by sexual contact or exchanging bodily fluids
  • Initially causes flu-like symptoms, then no symptoms for years
  • Attacks the immune cells, leading to late stage HIV infection (AIDS)
• Tobacco mosaic virus (TMV)


  • Virus that affects many plant species like tomatoes
  • Causes a mosaic pattern on the leaves, reducing photosynthesis and plant growth
• Rose black spot


  • Fungus that causes purple/black spots on rose leaves, leading to leaves turning yellow and dropping off
  • Reduces photosynthesis and plant growth
  • Spreads through water or wind
  • Can be treated with fungicides and removing affected leaves
• Malaria


  • Caused by a protist
  • Part of the protist's life cycle takes place inside mosquitoes, which act as vectors
  • Causes repeating episodes of fever, can be fatal
  • Spread can be reduced by stopping mosquito breeding and using insecticides/nets
• Salmonella


  • Bacteria that causes food poisoning
  • Infected people suffer fever, stomach cramps, vomiting and diarrhoea
  • Caused by toxins produced by the bacteria
  • Can be contracted from contaminated food, but poultry is vaccinated against it in the UK
• Gonorrhoea


  • Sexually transmitted bacterial disease
  • Causes pain when urinating and discharge
  • Originally treated with penicillin, but now strains are resistant
  • Can be prevented by using barrier contraception
• Ways to reduce/prevent disease spread


  • Being hygienic
  • Destroying vectors
  • Isolating infected individuals
  • Vaccination
• Human body's defences


  • Skin acts as a barrier and secretes antimicrobial substances
  • Hairs and mucus in nose trap particles
  • Trachea and bronchi secrete mucus and have cilia to trap pathogens
  • Stomach produces hydrochloric acid to kill pathogens
• White blood cells


  • Most important part of the immune system
  • Can consume and digest pathogens (phagocytosis)
  • Produce antibodies specific to pathogens
  • Produce antitoxins to counteract toxins
• Vaccination


  • Involves injecting small amounts of dead or inactive pathogens to stimulate antibody production
  • Allows rapid antibody response if exposed to live pathogens later
  • Has helped control many communicable diseases
  • Can prevent epidemics if enough people are vaccinated
  • But don't always work and can have rare bad reactions
• There are lots of communicable diseases that were once common in the UK (e.g. polio, measles, whooping cough, rubella, mumps, tetanus)
• Smallpox no longer occurs at all, and polio infections have fallen by 99%
• Epidemics


  Big outbreaks of disease
• Epidemics


  • Can be prevented if a large percentage of the population is vaccinated
  • If a significant number of people aren't vaccinated, the disease can spread quickly through them and lots of people will be ill at the same time
• Cons of vaccines


  • Vaccines don't always work - sometimes they don't give you immunity
  • You can sometimes have a bad reaction to a vaccine (e.g. swelling, or maybe something more serious like a fever or seizures)
• Bad reactions to vaccines are very rare
• Deciding whether to have a vaccination


  Balancing the risk of catching the disease if you don't have a vaccine, against the risk of having a bad reaction if you do
• Prevention is better than cure
• Painkillers


  Drugs that relieve pain, but don't actually tackle the cause of the disease or kill pathogens, they just help to reduce the symptoms
• Cold remedies


  Don't actually cure colds, they just reduce the symptoms
• Antibiotics


  Kill or prevent the growth of bacteria causing the problem without killing your own body cells
• Antibiotics don't destroy viruses (e.g. flu or cold viruses)
• The use of antibiotics has greatly reduced the number of deaths from communicable diseases caused by bacteria
• Developing new drugs


  1. Preclinical testing on human cells and tissues in the lab

  2. Testing on live animals to test efficacy, toxicity and find the best dosage

  3. Clinical trials on healthy volunteers and then people suffering from the illness
• The law in Britain states that any new drug must be tested on two different live mammals
• Some people think that animals are so different from humans that testing on animals is pointless
• Clinical trials


  1. Patients are randomly put into two groups - one gets the new drug, the other gets a placebo

  2. known as double blind trial - the patient doesn't know if they're getting the drug or placebo, neither does the doctor

  3. The results are published after peer review
• Monoclonal antibodies


  Identical antibodies produced from clones of a single white blood cell
• Producing monoclonal antibodies


  1. Mouse injected with chosen antigen

  2. Fast-dividing tumour cells from the lab fused with B-lymphocyte to create a hybridoma

  3. Hybridoma cells cloned to produce lots of identical cells that produce the same antibodies
• Uses of monoclonal antibodies


  • Can be used to target specific cells or chemicals in the body
  • Can be used in labs and research to measure chemical levels, test for pathogens, and locate specific molecules
• Monoclonal antibodies do cause more side effects than were originally expected, such as fever, vomiting and low blood pressure.
• Plants need mineral ions from the soil, and a lack of certain ions causes deficiency symptoms