Topic 3: Infection & Response

• Viruses


  • Very small
  • Move into cells and use the biochemistry to make many copies of itself
  • This leads to the cell bursting and releasing all of the copies into the bloodstream
  • The damage and the destruction of the cells makes the individual feel ill
• Bacteria


  • Small
  • Multiply very quickly through dividing by a process called binary fission
  • Produce toxins that can damage cells
• Protists


  • Some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage)
• Fungi


  • Can either be single celled or have a body made of hyphae (thread-like structures)
  • Can produce spores which can be 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 - pathogens can be carried in the air and then breathed in (a common example is the droplet infection, which is when sneezing, coughing or talking expels pathogens in droplets which can be breathed in)
• Ways to reduce the damage of disease to populations

  • Improving hygiene: Hand washing, using disinfectants, isolating raw meat, using tissues and handkerchiefs when sneezing
  • Reducing contact with infected individuals
  • Removing vectors: Using pesticides or insecticides and removing their habitat
  • Vaccination: By injecting a small amount of a harmless pathogen into an individual's body, they can become immune to it so it will not infect them. This means they cannot pass it on.
• Viruses


  Particularly dangerous as they can enter all types of cells, and scientists are yet to develop medicines to cure them
• Measles symptoms: Fever and red skin rash, can lead to other problems such as pneumonia (lung infection), encephalitis (brain infection) and blindness
• Measles prevention


  Vaccinations for young children to reduce transmission
• HIV symptoms


  Initially flu-like symptoms, then the virus attacks the immune system and leads to AIDS (a state in which the body is susceptible to many different diseases)
• HIV spread


  By sexual contact or exchange of bodily fluids such as blood
• HIV prevention


  • The spread- Using condoms, not sharing needles, screening blood when it is used in transfusions, mothers with HIV bottle-feeding their children instead of breastfeeding
  • The development to AIDS- Use of antiretroviral drugs (stop the virus replicating in the body)
• Tobacco mosaic virus (a plant pathogen affecting many species of plants including tomatoes) symptoms: Discolouration of the leaves, the affected part of the leaf cannot photosynthesise resulting in the reduction of the yield
• Tobacco mosaic virus spread


  Contact between diseased plants and healthy plants, insects act as vectors
• Tobacco mosaic virus prevention


  Good field hygiene and pest control, growing TMV-resistant strains
• Bacterial diseases are on the rise as they are becoming resistant to antibiotics
• Salmonella food poisoning symptoms: Fever, stomach cramps, vomiting, diarrhoea (all caused by the toxins they secrete)
• Salmonella food poisoning spread

  These bacteria can be found in raw meat and eggs, unhygienic conditions
• Salmonella food poisoning prevention

  • Poultry are vaccinated against Salmonella, keeping raw meat away from cooked food, avoid washing it, wash hands and surfaces when handling it, cook food thoroughly
• Gonorrhoea symptoms: Thick yellow or green discharge from the vagina or penis, pain when urinating
• Gonorrhoea spread


  It is a sexually transmitted disease spread through unprotected sexual contact
• Gonorrhoea prevention


  By using contraception such as condoms and antibiotics (used to be treated with penicillin but many resistant strains are developing)
• Rose black spot symptoms: Purple or black spots on leaves of rose plants, reduces the area of the leaf available for photosynthesis, leaves turn yellow and drop early
• Rose black spot spread


  The spores of the fungus are spread in water (rain) of by wind
• Rose black spot prevention

  By using fungicides or stripping the plant of affected leaves (have to be burnt)
• Malaria symptoms: Fevers and shaking (when the protists burst out of blood cells)
• Malaria spread


  The vector is the female Anopheles mosquito, in which the protists reproduce sexually. When the mosquito punctures the skin to feed on blood, the protists enter the human bloodstream via their saliva
• Malaria prevention


  • Using insecticide coated insect nets while sleeping, removing stagnant water to prevent the vectors from breeding, travellers taking antimalarial drugs to kill parasites that enter the blood
• Non-specific defence system


  • The skin acts as a physical barrier, produces antimicrobial secretions, and has good microorganisms known as skin flora
  • The nose has hairs and mucus which prevent particles from entering your lungs
  • The trachea and bronchi secrete mucus to trap pathogens and have cilia to waft mucus upwards
  • The stomach produces hydrochloric acid that kills any pathogens in your mucus, or food and drink
• Specific immune system actions

  • Phagocytosis (engulfing and consuming pathogens)
  • Producing antibodies
  • Producing antitoxins
• Vaccination


  Involves making an individual immune to a certain disease- they are protected against it before they have been infected. By immunising a large proportion of the population, the spread of the pathogen is reduced as there are less people to catch the disease from (called herd immunity)
• How vaccinations work


  The vaccine contains a dead or inactivated form of the pathogen, which stimulates white blood cells to produce antibodies complementary to the antigens on the pathogen
• Antibiotics are medicines that kill bacterial pathogens inside the body, without damaging body cells. They cannot kill viruses as they use body cells to reproduce, meaning any drugs that target them would affect body tissue too. Painkillers (such as aspirin) only treat the symptoms of the disease, rather than the cause
• Antibiotic use


  • They can be taken as a pill, syrup or directly into the bloodstream
  • Different antibiotics are effective against different types of bacteria, so receiving the correct one is important
  • Their use has decreased the number of deaths from bacterial diseases
• Antibiotic resistance


  Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics. When these bacteria are exposed to antibiotics, only the non-resistant one die. The resistant bacteria survive and reproduce, meaning the population of resistant bacteria increases. This means that antibiotics that were previously effective no longer work
• Ways to prevent antibiotic resistance

  • Stop overusing antibiotics- this unnecessarily exposes bacteria to the antibiotics
  • Finishing courses of antibiotics to kill all of the bacteria
• Many drugs were initially discovered in natural sources
• Bad reactions (such as fevers) can occur in response to vaccines (although very rare)
• The great concern is that bacteria are becoming resistant to antibiotics
• Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics


  1. When these bacteria are exposed to antibiotics, only the non-resistant one die

  2. The resistant bacteria survive and reproduce, meaning the population of resistant bacteria increases

  3. This means that antibiotics that were previously effective no longer work