Infection and response

• Pathogen


  Microbes that enter the body and cause disease
• Types of pathogen


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  • Very small living cells
  • Can reproduce rapidly inside the body
  • Can produce toxins that damage cells and tissues
• Viruses


  • Not cells, much smaller than bacteria
  • Can reproduce rapidly inside the body
  • Live inside cells and use the cell's machinery to replicate
  • Cell damage is what makes you feel ill
• Protists


  • Single-celled eukaryotes
  • Some are parasites that live in or on other organisms and can cause disease
  • Often transferred by vectors that don't get the disease
• Fungi


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

  • Water
  • Air
  • Direct contact
• How viruses cause cell damage

  1. Virus enters cell

  2. Virus uses cell's machinery to replicate

  3. Cell bursts, releasing new viruses
• Viral diseases


  • Measles
  • HIV
• Fungal disease


  • Rose black spot
• Protist disease


  • Malaria
• Antibiotic-resistant strains of bacteria have become harder to treat
• Chefs washing hands thoroughly before cooking

  Prevents the spread of disease
• Human body's defence system

  • Skin acts as a barrier
  • Nose and mucus trap particles
  • Stomach acid kills pathogens
• Immune system


  • White blood cells patrol the body
  • White blood cells can consume pathogens
  • White blood cells produce antibodies specific to pathogens
• If a person is infected with the same pathogen again, the white blood cells will rapidly produce antibodies to kill it
• White blood cells


  Important part of your immune system, found in your blood and circulate throughout your body constantly patrolling for invaders
• White blood cells' lines of attack against invading microbes

  1. Consuming them (phagocytosis)

  2. Producing antibodies

  3. Producing antitoxins
• Phagocytosis


  White blood cells engulfing and digesting foreign cells
• Producing antibodies


  1. Every invading pathogen has unique molecules (antigens) on its surface

  2. White blood cells produce proteins (antibodies) to bind to the invading antigens so they can be destroyed

  3. Antibodies are produced rapidly and carried around the body

  4. If infected again, white blood cells rapidly produce antibodies to kill the pathogen
• Producing antitoxins


  These counteract toxins produced by the invading bacteria
• If you have a low level of white blood cells, you'll be more susceptible to infections
• HIV attacks white blood cells and weakens the immune system, making it easier for other pathogens to infect
• Vaccinations have changed the way we fight disease
• Vaccination


  1. Allows your white blood cells time to learn how to deal with a pathogen

  2. Involves injecting dead or weakened pathogens, which cause your body to produce antibodies to affect them

  3. If the same pathogens try to attack later, the white blood cells can rapidly reproduce antibodies to kill them off
• Pros of vaccination


  • Vaccines have helped prevent lots of deadly diseases
  • Outbreaks of epidemics can be prevented if a large proportion of the population is vaccinated
• Cons of vaccination


  • Vaccines don't always work
  • You can sometimes have a bad reaction to a vaccine
• Drugs that relieve symptoms


  Don't tackle the cause of the disease or kill pathogens, just help reduce symptoms
• Antibiotics


  Work by killing or preventing the growth of the bacteria causing the problem, without killing your own body cells
• Antibiotics don't work on viruses, as viruses reproduce inside your body's cells which makes it very difficult to develop drugs that destroy just the virus without killing the body's cells
• The use of antibiotics has greatly reduced the number of deaths from diseases caused by bacteria
• Bacteria becoming resistant to antibiotics

  1. Some bacteria mutate to become resistant to antibiotics

  2. When an infection is treated, only the resistant strains survive

  3. The resistant strains then multiply, making the infection harder to treat
• E. coli (MRSA) causes serious wound infections and is resistant to the powerful antibiotic methicillin
• To slow the development of resistant strains, it's important for doctors to avoid over-prescribing antibiotics and for patients to finish the full course of antibiotics
• Many drugs were originally discovered by studying chemicals from plants used in traditional medicine
• Alexander Fleming discovered penicillin from a mould that killed bacteria in a Petri dish
• Stages of drug testing

  1. Preclinical testing on cells and tissues in the lab

  2. Animal testing to check safety and effectiveness

  3. Clinical trials on healthy volunteers to check safety

  4. Clinical trials on patients to check effectiveness

  5. Trials are double-blind so neither patients nor doctors know who is getting the drug or placebo
• The results of drug trials are not published until they have been through rigorous peer review
• Placebo


  A substance that looks like the drug being tested but doesn't do anything
• Placebo effect


  When the patient perceives the treatment to work even though the placebo isn't doing anything