b3 - infection and response

• pathogen

  microorganisms that causes infectious diseases

  may infect plants or animals and can be spread by direct

  contact, by water or by air

  the four types: bacteria, virus, fungi, protist
• bacteria


  reproduces rapidly inside the body

  may produces poisons (toxins) that damage tissues and makes us feel ill
• virus


  virus may reproduce rapidly inside the body

  live and reproduce inside cells, causing cell damage
• measles


  pathogen: virus

  symptoms: fever and a red rash - can be fatal

  how is it spread: inhaling droplets from sneezes and coughs

  treatment/reducing spread: vaccination reduces spread of the pathogen
• HIV


  pathogen: virus

  symptoms: flu-like illness. if developed into AIDS, immune system is damaged so it can't deal with other infections or cancers

  how is it spread: sexual contact, exchange of body fluids

  treatment/reducing spread: controlled with antiretroviral drugs
• tobacco mosaic virus (tmv)


  pathogen: virus

  symptoms: mosaic pattern of discolouration on leaves. chlorophyll is therefore destroyed which means less photosynthesis, less glucose made for respiration and reduced growth as it will absorb less light

  how is it spread: contact between plants

  treatment/reducing spread: destroy diseased plants
• salmonella


  pathogen: bacteria

  symptoms: fever, abdominal cramps, vomiting and diarrhoea

  how is it spread: bacteria is ingested from food or food is prepared in unhygienic conditions

  treatment/reducing spread: poultry are vaccinated against salmonella. food should be cooked thoroughly in hygienic conditions
• gonorrhoea


  pathogen: bacteria

  symptoms: thick yellow or green discharge from vagina or penis. pain when urinating

  how is it spread: sexual contact - gonorrhoea is an STD

  treatment/reducing spread: antibiotics (though some bacteria is antibiotic resistant), using barrier method of contraception (condom)
• rose black spot


  pathogen: fungus

  symptoms: purple or black spots on leaves, often turn yellow and drop early. less photosynthesis - less glucose made for respiration - reduced growth for plant

  how is it spread: water or by wind (air)

  treatment/reducing spread: using fungicides or removing and destroying the affected leaves
• malaria


  pathogen: protist

  symptoms: fever - can be fatal

  how it is spread: being bitten by a vector (mosquito) carrying blood infected with the protist

  treatment/reducing spread: preventing the vectors, mosquitoes, from breeding. avoid being bitten - using mosquito nets or insect repellent
• human defence system


  skin - prevents the entry of pathogens by forming a barrier. it heals cuts quickly by forming a scab to prevent entry of pathogens

  stomach - contains hydrochloric acid which kills pathogens

  lysozyme (enzyme) - found in tears and saliva - breaks down and destroys pathogens

  trachea - produces mucus which traps pathogens. also lined with cilia cells which move the mucus and trapped pathogens up to the back of throat where it is coughed out
• phagocytes


  white blood cells which engulf and digests pathogens
• lymphocytes


  white blood cells which detect pathogens by recognising the antigen (chemical marker) on the surface of the pathogen. produces antibodies which bind to the antigens of the pathogen and clump them so they can be destroyed
• antitoxins


  white blood cells which destroy toxins that pathogens release into the body
• what does vaccinations do


  prevents illness in an individual by making them immune to a certain pathogen
• stages of vaccination

  1. small quantity of dead or inactive forms of a pathogen is injected into the body
  2. the lymphocytes are stimulated to produce complementary antibodies which bind to the antigens of the pathogens and destroy them
  3. memory lymphocytes remain in the blood and if the same pathogen re-enters the body the white blood ells respond quickly to produce quickly to produce the correct antibodies, preventing infection
• penecillin

  first antibiotic discovered

  discovered by alexander fleming - noticed that bacteria growing in a petri dish had been killed by a patch of penicillium.
• antibiotics


  greatly reduces deaths from infectious bacterial diseases

  some strains of antibiotic resistant bacteria have developed which are difficult to kill

  cannot kill viruses as viral pathogen found within cells - it would damage the body's tissues
• discovery of drugs

  digitalis - heart drug, originates from foxglove flowers

  aspirin - painkiller, originates from willow tree

  penicillin - originates from penicillium mould
• development of drugs


  traditionally - drugs extracted from plants and microorganism

  nowadays - drugs are synthesised by chemists in the pharmaceutical industry
• 3 things drugs are tested for

  toxicity - if the drug has harmful side effects

  efficacy - if the drug works well to treat the disease

  dose - how much drug needs to be taken and how often
• pre-clinical testing (stage 1 and 2)

  after the potential new drug is discovered, it is analysed using a computer simulation. then it is tested in a laboratory using cells, tissues and live animals.
• clinical trials (stage 3)

  in the first phase of stage 3, healthy volunteers are used and low doses are given to them.

  low doses are required to look for and reduce the risk of side effects.

  healthy people are used so it is less risky if there are side effects. it is also easier to identify side effects as they dont have any other symptoms

  trials are double blind trials, some patients are given a placebo or the real drug. this all to prevent psychological bias
• final stage (stage 4)

  analysis of results and findings are peer-reviewed. this is to check if results are valid and to avoid bias. the drug is then licenced if all is okay