communicable diseases

• what are communicable diseases

  • are caused by infective organisms known as pathogens
• types of pathogens

  • bacteria
  • virus
  • fungi
  • protoctista
• a communicable disease can be passed from one organisms to another but also be spread between species
• bacteria

  • prokaryotes
  • divide rapidly by binary fission
  • damage cells by producing waste products which are toxic to the host
• viruses

  • tiny, non-living particles containing strands of DNA or RNA
  • enter and take over genetic machinery and organelles of host cells forcing it to make copies of the virus
  • cell bursts releasing these copies of viruses into the host
• fungi

  • eukaryotic organisms which grow on hosts, especially plants
  • they cause diseases by releasing enzyme which digest living cells, may produce toxins which damage cells
• Protoctista

  • eukaryotic single celled organisms which live in a hosts cell eating and reproduce in others
• bacteria examples

  • tuberculosis (TB)
  • bacterial meningitis
  • ring rot
• TB

  • killing cells and tissues, lungs are more often affected
  • bacteria: M.bovis
• bacterial meningitis

  • bacteria in the membranes that surround the brain and the spinal cord, causes it to become swollen and can cause damage to the brain and the nerves
• ring rot (in plants)

  • damages leaf, tubers and fruit of potatoes and tomatoes
• types of viruses

  • influenza
  • HIV/AIDS
  • Tobacco mosaic virus
• influenza

  • attacks respiratory system
  • muscle pain
  • headaches
  • prevented by : vaccinations
• AIDS

  • break down of the immune system
• tobacco mosaic virus (plants)

  • mosaic pattern of discolouration on leaves
• types of fungi

  • black sigatoka (banana)
  • athletes foot
  • ring worm
• black sigatoka

  • causes black spots on leaves of banana plants
• athletes foot

  • growth under skin of feet - toes
• ring worm (cattle)

  • rashes and soreness on skin of cattle
• types of Protoctista

  • potato late blight
  • malaria
• potatoes late blight

  • affects both both leaves and potato tubers
• malaria

  • fever, weakness, coma
• pathogens can be transmitted from an infected individual to an uninfected one in a direct or an indirect way
• types of direct transmission

  • droplet/aerosol
  • direct physical contact
  • ingestion
• droplet/aerosol

  • tiny water droplets containing the pathogen produced when coughing or sneezing
  • eg influenza, TB
  • cover mouth when coughing or sneezing
• direct physical contact

  • transmission via skin to skin contact or via body fluid
  • eg meningitis, ringworm or athletes foot
  • good personal hygiene, using condoms
• ingestion

  • eating food directly contaminated by an infected person during preparation
  • hand washing, hygienic food prepartion
• types of indirect transmission

  • vectors
  • fomites
  • water
• vectors

  • insects such as mosquitoes carry pathogen from one host to another
  • eg malaria, yellow fever
  • kill the vector, avoid contact with the vector
• fomites (inanimate objects)

  • pathogen transfer via objects like door handles, towels, bedding
  • eg athletes foot
  • need good personal hygiene
• water

  • drinking contaminated water with sewage
  • cholera
  • effective water treatment
• zoonotic transmission

  • disease that humans catch from an animal is known as zoonosis
  • occurs when a virus that normally infects an animal mutation and infects human cells
  • eg swine flue pigs to humans
• other factors affecting disease transmission

  • overcrowding
  • poor ventilation
  • poor hygiene
  • homelessness
  • lack of clean water supply
  • migration
  • climate change
  • poor health and nutrients
• preventing the spread of infectious disease

  • providing clean water
  • vaccinating programmes
  • killing vectors
  • isolating the individual
• disease transmission in plants = direct

  • leaves touching
• indirect transmission in plants

  • contaminated soil - pathogens remain in soil after the removal of infected plants
  • vectors eg insects covered in pathogen
• plant defences

  • active defences
  • passive defences
  • physical defences
• active defences

  • defences produced in direct response to an attack of a pathogen
  • when pathogens attack, specific chemicals in their cell wall can be detected by the plants cells - proteins and glycolipids
• physical defences

  • these are generally bark that prevent the entry of pathogen
• chemical defences

  • some chemicals like bitter testing - tanning and alkaloids are always present and help to stop animals eating the plants to reduce damage that could allow pathogens to enter