infection and response P1

• Types of disease-causing pathogens

  • Viruses
  • Bacteria
  • Protists
  • Fungi
• Pathogens

  Microorganisms that cause infectious, communicable diseases
• How pathogens can be spread

  • Contact
  • Water or air
  • Vectors (organisms that carry and pass on the pathogen without getting the disease)
• Ways to reduce the spread of infectious diseases

  • Simple hygiene measures, eg. washing hands and sneezing into a handkerchief
  • Destroying vectors
  • Isolating infected individuals, so they cannot pass the pathogen on
  • Giving people at risk a vaccination
• Viruses

  Reproduce rapidly in body cells, causing damage to the cell
• Measles


  A disease caused by a virus, with symptoms of fever and a red skin rash, spread by breathing in droplets from sneezes and coughs
• Although most people recover well from measles, it can be fatal if there are complications, so most young children are vaccinated against measles
• HIV (human immunodeficiency virus)


  Causes AIDS, spread by sexual contact or exchange of body fluids, initially causes a flu-like illness, if untreated attacks the body's immune cells, late stage is when the immune system is damaged and cannot fight off other infections or cancers
• Tobacco mosaic virus (TMV)


  Occurs in tobacco plants and many other species, including tomatoes, causes a distinctive mosaic pattern of discolouration that reduces the chlorophyll content of leaves, affecting photosynthesis and plant growth
• It is not the HIV virus that directly kills people with AIDS, but other infections, such as pneumonia, that a healthy body would usually be able to survive
• Bacteria


  May damage cells directly or produce toxins (poisons that damage tissues)
• Salmonella


  A type of food poisoning caused by bacteria, ingested in food that may not have been cooked properly or prepared in hygienic conditions, causes fever, abdominal cramps, vomiting and diarrhoea
• Chicken and eggs can contain the salmonella bacteria, so chickens in the UK are vaccinated against salmonella to control the spread
• Gonorrhoea


  A sexually transmitted disease (STD) caused by bacteria, spread by sexual contact, causes a thick, yellow or green discharge from the vagina or penis and pain when urinating, used to be easily treated with antibiotics but many resistant strains have now appeared
• The use of a barrier method of contraception, eg a condom, can stop the gonorrhoea bacteria being passed on, and completing antibiotic treatment can also stop the spread
• Protists


  Single-celled organisms, unlike bacteria they are eukaryotic
• Malaria


  Caused by a protist that uses a particular type of mosquito as a vector, passed on to a person when they are bitten by the mosquito, causes severe fever which reoccurs and can be fatal
• One of the main ways to stop the spread of malaria is to stop people being bitten, eg. by killing the mosquitoes or using mosquito nets
• Rose black spot


  A fungal disease, spread when spores are carried from plant to plant by water or wind, causes purple or black spots on leaves which often turn yellow and drop early, reducing photosynthesis and stunting plant growth
• Rose black spot can be treated by using fungicides and removing and destroying the affected leaves
• Simple precautions like sneezing into a handkerchief can stop pathogens being spread by droplets in the air
• It is important to keep uncooked meat separate from cooked meat to prevent the spread of bacteria like salmonella
• The contraceptive pill does not prevent the spread of gonorrhoea, as it is a sexually transmitted disease
• Leaves infected with rose black spot should be removed and burned to stop the spread of the fungal disease
• Non-specific defences against pathogens

  • Mucus trapping particles
  • Cilia creating a mucus movement
  • Enzymes in tears destroying pathogens
  • Skin as a physical barrier
  • Stomach acid killing bacteria
  • Sebum killing bacteria and fungi
• Phagocytosis


  White blood cells surrounding, engulfing and digesting pathogens
• Antibodies


  Special protein molecules produced by white blood cells that attach to antigens on pathogens
• Antitoxins


  Chemicals produced by white blood cells that neutralise the poisonous effects of toxins
• Immunity


  The quick response of white blood cells to produce the correct antibodies when a pathogen re-enters the body, preventing the person from getting ill
• Vaccination


  Injecting small quantities of dead or inactive forms of a pathogen to stimulate white blood cells to produce antibodies and develop immunity
• The disease smallpox does not exist anymore because vaccination managed to prevent the pathogen spreading to new hosts, and scientists are hoping to repeat this with polio
• Some vaccinations do carry a very small risk of side effects, but it is important to compare this with the risk of getting the disease
• The stomach helps to kill pathogens by producing hydrochloric acid
• Phagocytosis is the process where white blood cells surround, engulf and digest pathogens
• Antibodies are the protein molecules made by white blood cells when they detect a pathogen
• Vaccination uses a dead or weakened pathogen to stimulate the immune system to produce antibodies and develop immunity
• Antibiotics can only kill bacteria, they cannot destroy viruses
• MRSA

  A strain of bacteria that is resistant to antibiotics
• To reduce the rate at which resistant strains of bacteria develop, doctors should not prescribe antibiotics unless they are really needed, for non-serious infections, or for viral infections, and patients must complete their course of antibiotics so that all bacteria are killed and none survive to form resistant strains
• New painkillers are developed to treat the symptoms of disease but they do not kill the pathogens