Communicable diseases

• What are pathogens?

  • Microorganisms that can cause disease
• Name three ways pathogens can spread?

  • Air
  • Water
  • Direct contact
• What are the four main types of pathogen?

  • Bacteria
  • Fungi
  • Protists
  • Viruses
• How can the spread of disease be reduced?

  • Being hygienic
  • Destroying vectors
  • Isolating infected individuals
  • Vaccination
• Bacteria

  • Very small cells which can reproduce rapidly inside your body
  • Can make you feel ill by producing toxins that damage your cells and tissues
• Viruses

  • Are not cells
  • When they have infected a suitable host cell or cells, they replicate themselves using the cell's machinery
  • The cells will usually the burst releasing all the new viruses → go on to infect neighbouring cells
• Protists

  • They are all eukaryotes
  • Most of them are single-celled
  • Some protists are parasites
• Fungi

  • Some fungi are single-celled
  • Others have a body which is made up of hyphae
• Name three viral diseases

  • Measles
  • HIV
  • Tobacco Mosaic Virus
• Name two bacterial diseases

  • Salmonella
  • Gonorrhea
• Name a fungal disease

  • Rose black spot
• Name a disease caused by a protist

  • Malaria
• What is a vector?

  • Any organism that can spread a disease
• Measles

  • A viral disease
  • Spread by tiny droplets from an infected person's sneeze or cough
  • People with measles develop a red skin rash and a fever
  • It is a serious illness that can be fatal if complications arise
• HIV

  • It is a viral disease
  • It's spread by sexual contact or exchange of body fluids 
  • Initially causes a flu-like illness
  • HIV can be controlled with antiretroviral drugs
  • AIDS occurs when the body's immune system becomes so badly damaged, it can't cope with other infections or cancers
• Tobacco Mosaic Virus

  • A virus that affects many species of plants e.g. tomatoes
  • Causes a mosaic pattern on the leaves of plants  → parts of the leaves become discoloured
  • Discolouration means that photosynthesis can't take place, so the virus affects growth
  • Transmitted by contact between plants
• Salmonella

  • A type of bacteria that causes food poisoning
  • Infected people can suffer from fever, stomach cramps, vomiting and diarrhoea
  • Symptoms are caused by the bacteria and the toxins they secrete
• Gonorrhea

  • A bacterial disease
  • It is a sexually transmitted disease (STD)
  • Symptoms are a thick yellow or green discharge from the vagina or penis and pain when urinating
  • The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom
• Rose black spot

  • A fungus that causes purple or black spots on leaves → leaves can turn yellow and drop early
  • Less photosynthesis can happen so plant doesn't grow very well
  • It is spread in the environment by water or wind
  • Can be treated by using fungicides and removing and destroying the affected leaves
• Malaria

  • Caused by a protist
  • The mosquitoes are vectors → they pick up the malarial protist when they feed on an infected animal → inserts the protist into another animal's blood vessels
  • Causes recurrent episodes of fever and can be fatal
  • Can be controlled by preventing the vectors, mosquitos, from breeding 
  • People can be protected from mosquitoes using mosquito nets and insecticides
• Non specific human defence systems against disease

  • Skin - acts as a physical barrier to pathogens and secretes antimicrobial substances which kill pathogens
  • Nose - hair and mucus in your nose trap particles that could contain pathogens
  • Trachea and bronchi - secrete mucus to trap pathogens and is lined with cilia which waft the mucus up to the back of the throat where it is swallowed into your stomach
  • Stomach - produces hydrochloric acid which kills pathogens
• The immune system of the human body in defence against disease

  • phagocytosis - white blood cells engulf foreign cells and digest them
  • antibody production - lock on to invading cells so that they can be found and destroyed by phagocytes
  • antitoxin production - counteract toxins by invading bacteria
• What is vaccination?

  • Vaccination involves introducing small quantities of dead or inactive forms of a pathogen into the body to stimulate the white blood cells to produce antibodies. If the same pathogen re-enters the body the white blood cells respond quickly to produce the correct antibodies, preventing infection.
• What are the pros of vaccines?

  • Have helped control lots of communicable diseases that were once common in the UK e.g. polio
  • Epidemics can be prevented if a large percentage of the population is vaccinated
• What are the cons of vaccines?

  • Vaccines don't always give you immunity
  • You can have a bad reaction to a vaccine e.g. swelling
• What are painkillers?

  • Drugs that relieve pain
  • Helps to reduce the symptoms
• What are antibiotics?

  • Medicines that help to cure bacterial diseases by killing infective bacteria inside the body
  • Different antibiotics kill different types of bacteria
• The discovery of drugs

  • The heart dug originates from foxgloves
  • The painkiller aspirin originates from willow
  • Penicillin was discovered by Alexander Fleming from the penicillium mould
• What are new drugs extensively tested for?

  • Efficacy: how well the drug works and if it produces the effect you're looking for
  • Toxicity: how harmful the drug is and the side effects
  • Dosage: the concentration that should be given and how often
• Preclinical testing (done in a laboratory)

  1. Drugs are tested on human cells and tissues
  2. Drugs are tested on live animals -to test efficacy and toxicity
• Clinical trials (using healthy volunteers and patients)

  1. At the start of the trial, a very low dose of the drug is given and this is gradually increased
  2. If the drug is found to be safe, the drugs can be tested on people suffering from the illness to find the optimum dose