infection and response

• pathogens are microorganisms that can cause infectious disease
• viruses

  • very small
  • move into cells and clone
  • cell then bursts releasing copies into bloodstream
  • damage and destruction of cells makes person feel ill
• bacteria

  • small
  • multiply quickly through binary fission
  • produce toxins which damage cells
• protists

  • parasitic, using human and animals as hosts
  • live on or inside the host
• fungi

  • single celled or have a body made of hyphae
  • produce spores which spread to other organisms
• ways pathogens are spread

  • direct contact - touching contaminated surfaces
  • by water - drinking or coming into contact with dirty water
  • by air - carried in air then breathed in
• ways to limit the spread of pathogens

  • improving hygiene
  • reducing contact with infected individuals
  • removing vectors with pesticides
  • vaccination
• viruses are dangerous as they can enter all types of cells
• viruses - measles

  • symptoms are fever and red rash on skin
  • spread by droplet infection
  • prevented by vaccinations for young children
• viruses - HIV

  • symptoms similar to flu then immune system is hit causing AIDS
  • spread by sexual contact or exchange of bodily fluids
  • prevented by not sharing needles and condoms
  • AIDS development can be prevented using antiretroviral drugs
• viruses - tobacco mosaic virus

  • symptoms are discoloration of leaves so plant can't photosynthesise so yield is reduced
  • spread by contact with diseased plants and healthy ones, spread by vectors
  • prevented by good field hygiene and pest control
• bacterial diseases - salmonella

  • symptoms are fever, cramps, vomiting and diarrhoea
  • spread by bacteria in raw meat, eggs or unhygienic conditions
  • prevented by poultry vaccinations, keep raw meat from cooked meat, cook thoroughly, wash hands
• bacterial disease - gonorrhoea

  • thick yellow or green discharge from vagina or penis
  • pain when urinating
  • spread by sexual transmission due to unprotected sex
  • prevented by using contraception and penicillin
• fungal disease - rose black spot

  • symptoms are purple or black spots on leaves, photosynthesis cannot occur so leaves turn yellow and drop
  • spread by spores in rain or wind
  • prevented by fungicides or stripping plant of affected leaves
• protist diseases - malaria

  • caused by pathogens entering red blood cells, damaging them
  • spread by female mosquito where protist reproduce sexually
  • protist enter human blood via saliva
  • prevented by insecticides, insect nets, remove stagnant water and taking antimalarial drugs
• human defence system - skin

  • acts as a physical barrier
  • produces antimicrobial secretions to kill pathogens
  • good microorganisms such as skin flora compete with bad ones
• human defence system - nose

  • has hairs and mucus to prevent particles from entering the lungs
  • sneezing
• human defence system - trachea and bronchi

  • secrete mucus to trap pathogens
  • cilia beat to waft mucus upwards so it can be swallowed or coughed
• specific immune system - phagocytosis

  • engulfing and consuming pathogens
  • destroys pathogens so you no longer feel ill
• specific immune system - producing antibodies

  • each pathogen has an antigen on the surface
  • this antigen has a complimentary antibody which it binds to
  • antibodies bind to pathogens which clump so white blood cells find them easily
  • if infected again the antibodies produce at a faster rate as they recognise the pathogen so they are immune now
• specific immune system - producing antitoxins

  • neutralise toxins released by pathogens by binding to them
• vaccinations make individuals immune to certain diseases
• by immunising a population through vaccination, the spread of the pathogen is reduced so less people catch it, this is herd immunity
• vaccinations replicate the first infection so that when a person is exposed to the real disease they do not feel any symptoms
• how vaccinations work

  • vaccine contains a dead or inactive form of the pathogen
  • this stimulates white blood cells to produce antibodies complementary to the antigens on the pathogen
• advantages of vaccination

  • eradicated many diseases so far
  • reduces the occurence of many
• disadvantages of vaccination

  • not always effective in providing immunity
  • bad reactions can occur in response to vaccines
• antibiotics are medicines that kill bacterial pathogens without damaging body cells
• antibiotics cannot kill viruses as they use body cells to reproduce meaning drugs that target them would affect body tissue too
• painkillers only treat symptoms of disease rather than the cause
• how resistant bacteria work

  • mutations occur during reproduction resulting in certain bacteria no longer being killed by antibiotics
  • when these bacteria are exposed to antibiotics only non-resistant die
  • resistant bacteria survive and reproduce so population of resistant bacteria increases
  • antibiotics that were previously effective no longer work
• how to prevent development of resistant bacteria strains

  • stop overusing antibiotics
  • finish courses of antibiotics
• drugs today are mainly synthesised by chemists
• drugs must be tested for toxicity, efficacy and optimal dosage using preclinical testing and clinical trials
• aspirin is a painkiller originating from willow
• digitalis is used to treat heart problems originating from foxglove
• discovery of penicillin

  • Alexander Fleming grew bacteria on plates
  • he found the mould on his culture plates with clear rings around indicated there was no longer bacteria there
  • he found that the mould produced penicillin which kills bacteria
• preclinical testing

  • uses cells, tissues and live animals
• clinical testing

  • uses volunteers and patients
• process of clinical testing

  • first tested on healthy volunteers with low dose to test for harmful side effects
  • drugs are then tested on patients to determine effective dose
  • patients put in two groups, one receive placebo and the other receives actual drug to observe its effect
  • these single or double blind trials mean bias is removed
  • results are then peer reviewed for repeatability