Communicable diseases

• Types of pathogens 


  • Bacteria
  • Viruses
  • Protocista
  • Fungi
• vectors

  carry pathogens from one organism to another
• bacteria

  more bacteria than any other organism. a small proportion of these bacteria are pathogens, causing communicable diseases. they are prokaryotes so do not have a membrane-bound nucleus or organelles. can be classified in two main ways.

  • basic shape - they may be rod shaped, spherical, comma shaped, spiralled and corkscrew
  • cell walls - two main types of bacterial cell walls have different structures and react different with a process called gram staining. following staining gram positive bacteria look purple-blue under the light microscope. gram negative appear red.
• viruses

  are non-living infectious agents. they are around 50 times smaller in length than the average bacterium. the basic structure of a virus is some genetic material(DNA or RNA) surrounded by protein. viruses invade living cells, where the genetic material of the virus takes over the biochemistry of the host cell to make more viruses. viruses produce rapidly and evolve by developing adaptations to their host, which makes them very successful pathogens. they cause disease in every type of organism. there are even viruses that attack bacteria.
• Protoctista

  Are a group of eukaryotic organisms with a variety of feeding methods. They include single-celled organism and cells grouped into colonies. A small percentage of protoctista act as pathogens, causing devastating communicable disease. The protists which cause disease are parasitic- they use people or animals as their hosts organisms. Pathogenic protists may need a vector to transfer them to the hosts, or they may enter the body directly through polluted water.
• fungi

  fungal diseases are nit major problems in animals, but can cause devastation in plants. fungi are eukaryotic organisms that are often multicellular. fungi cannot photosynthesise and the digest their food extracellularly before absorbing the nutrients. many fungi are saprophytes which means they feed on dead and decaying matter. some fungi are parasitic, feeding on living plants and animals. these are pathogenic fungi which cause communicable diseases. fungal infections often affect the leaves of plants, they stop photosynthesising and so can quickly kill the plant.
• pathogens mode of actions

  • damaging the host tissue directly
  • producing toxins which damage host tissues
• pathogen mode of action - damaging the host tissues directly

  • viruses take over the metabolism - the viral genetic material gets into the host cell and is inserted into the host DNA. the virus then uses the host cell to make new viruses which them burst out of the cell, destroying it and them spread it to infect other cells
  • some protoctista also take over cells and break them open as the new generation emerge, but do not take over the genetic material of the cell. they simply digest and use the cell contents as they reproduce
  • fungi digest living cells and destroy them.
• pathogen mode of action - producing toxins which damage hot tissue

  • most bacteria produce toxins that poison or damage the host cells in some way, causing disease. some bacterial toxins damage he host cells by breaking down the cell membranes, some damage or inactivate enzymes and some interfere with the host cell genetic material so the cells cannot divide. these toxins are a by-produce of the normal functioning of the bacteria
  • some cells produce toxins which affect the host cells are cause disease
• plant diseases

  • ring rot
  • tobacco mosaic virus
  • potato blight
  • black Sigatoka
• Ring rot

  A bacterial disease of potatoes, tomatoes and aubergines caused by the gram positive bacterium. It damages leaves, tubers and fruit. It can destroy up to 80% of the crop and there is no cure. Once bacterial ring rot infects a field it cannot be used to grow potatoes again for at least two years.
• tobacco mosaic virus (TMV)

  a virus that infect tobacco plants and around 150 other species including tomatoes, peppers, cucumbers, petunias and delphiniums. it damages leaves, flowers and fruit, stunting growth and reducing yields, and can lead to an almost total crop loss resistant crop strains are available but their is no cure.
• potato blight (tomato blight and late blight)

  cause by the fugus like protoctist. the hyphae penetrate host cells, destroying leaves, tubers, and fruit, causing millions oof pounds worth of crop damage each year. there is no cure by resistant strains, careful management and chemical treatment can reduce infection risk
• black Sigatoka

  a banana disease cause by a fungus. which attacks and destroys leaves. the hyphae penetrate and digest the cells, turning ht e leaves black. if plants are infected it ca cause a 50% reduction in yield. resistant strains are being developed - good husbandry and fungicide
• Tuberculosis (TB)

  A bacterial disease of humans, cows, pigs, badgers, and deer. TB damages and destroys lung tissue and suppresses the immune system, so the body is less likely to fight off other diseases. Worldwide in 2012 around 8.6 million had TB 1.3 million died. The global rise of HIV/AIDS has had a big impact on the numbers of people also suffering from diseases such as TB, because people affected by HIV/AIDS are much more likely to develop TB infections. In people TB is both curable (by antibiotics) and preventable (by improving living standards and vaccinations)
• Bacterial meningitis

  A bacterial infection of the meninges of the brain (protective membranes membrane on the Surface of the brain),which can spread too the rest of the body causing septicaemia (blood poisoning) and rapid death. It mainly affects young children and teenagers aged 15-19. They have different symptoms but in both, a blotchy red/purple rash that does not disappear when glass is pressed against it (symptom of septicaemia), immediate treatment is needed. Antibiotics will cure the disease if delivered early. Vaccines can protect against some forms of bacterial meningitis
• HIV/AIDS

  caused by a virus which targets T helper cells in the immune system of the body. it gradually destroys the immune system so affected people are open to other infections, such as TB. HIV is a retrovirus with RNA as its genetic material. it contains the enzyme reveres transcriptase, which transcribes the RNA to a single strand of DNA to produce a single strand DNA to produce a single strand in the host cell, this DNA interacts with the genetic material of the host cell. the virus is passed through bodily fluids. there is no cure or vaccine
• influenza (flu)

  a viral infection of the ciliates epithelial cells in the gas exchange system. it kills them, leaving the airway open to secondary infection. Flu can be fatal especially in young children, many of the people who die re from server econdary infections. There are three main strains - A,B and C.
• Malaria

  Cause by protoctista spread by the bites of mosquitoes. They reproduce inside the female mosquito. The female needs to take two blood ,eats to provide her with protein before she layers her eggs - and this is when it is passed on to people. It invades the red blood cells, liver and even the brain. the disease, recurs, making people weak and vulnerable to other infection. There is no vaccine against malaria and limited cures, but preventative measures can be very effective. The key is to control the vector.
• ring worm

  a fungal disease affecting mammals including cattle, dogs, cats and humans. different fungi infect different species. it causes grey-white, crusty, infectious, circular ares of skin. it is not damaging but looks unsightly and may be itchy. anti fungal creams are an effective cure.
• athletes foot

  a human fungal disease, a form of ring worm that grows and digests the warm, most skin between the toes. it causes cracking and scaling, which is itchy and may become sore. anti fungal creams are an effective cure.
• transmission of pathogens between animals

  • direct transmission
  • indirect transmission
• types of direct transmission

  • direct contact
  • inoculation
  • ingestion
• direct contact

  • kissing or any contact with t he bodily fluids of anther person
  • direct skin-to-skin contact
  • microorganism from faeces transmitted on the hands
• inoculation

  • through a break in the skin
  • from an animal bite
  • through a puncture wound or through sharing needles
• ingestion

  taking in contaminated food or drink, or transferring pathogens to the mouth from the hands
• types of indirect transmission

  • fomites
  • droplet infection
  • vectors
• fomites

  inanimate objects such as as bedding, socks or cosmetics can transfer pathogens
• droplet infection (inhalation)

  minute droplets of saliva and mucus are expelled from your mouth as you talk, cough or sneeze. if these droplets contain pathogens, when healthy individuals breathes the droplets in they may become infected
• vectors

  • a vector transmits communicable pathogens from one host it another. vectors are often but not always animals
  • water can also act as a vector of disease
• Transmission between animals and humans

  Some communicable dieasease can be transferred between animals nd human, e.g. Bird flu. Minimising close contact with animals and washing hands throughly following any such contact can reduce infection rates. People can also act as vectors of some animal diseases, sometimes with fatal results.
• factors affecting the transmission of communicable diseases in animals

  • overcrowded living and working conditions
  • poor nutrition
  • a compromised immune system, including (in human) having HIV/AIDS or needing immunosuppressant drugs after transplant surgery
  • (inhalation humans) poor disposal of waste, providing breeding sites for vectors
  • climate change - this can introduce new vectors and new diseases, e.g. increased temperature promotes the spread of malaria
  • culture and infrastructure - in many countries traditional medical practices can increase transmission
• Transmission of pathogens between plants

  Plants do not move around, cough or sneeze, yet disease spread rapidly through plant communities, plant pollen and seed. Plants also have a less developed immune system than humans.
• direct transmission in plants

  this involves direct contact of a healthy plant with any part of a diseased plant. e.g. ring rot, tobacco mosaic virus.
• types of indirect transport in plants

  • soil contamination
  • vectors
• soil contamination in plants

  infected plants often leave pathogens (bacteria or viruses) or reproductive spores from protoctista or fungi in the soil. these can infect the next crop. some pathogens (often in spores) can survive the composting process so the infection cycle an be complete when the contaminated compost is used.
• vectors in plants

  • wind - spores may be carried in the wind to other crops
  • water - spores swim in the surface film of water on leaves; raindrop splashes carry pathogens and spores which swim over films of water on the leaves
  • animals - insects an birds carry pathogens and spores from one plant to another as they feed
  • humans - pathogens and spores transmitted by hands, clothing, fomites, farming practices and by transporting plants and crops around the world
• factor affecting the transmission of communicable diseases in plants

  • planting a variety of crops that a re susceptible to disease
  • over-crowding increases the likelihood of contact
  • poor mineral nutrition reduces resistance of plants
  • damp, arm conditions increase the survival and spread. of pathogens and spores
  • climate change - increased rainfall and wind promote the spread of diseases; changing conditions allow animal vectors to spread to new areas; driver conditions may reduce the spread of disease
• plant defence against pathogens - recognising an attack

  plants are not passive - they respond rapidly to pathogen attack. receptors in the cells respond to molecules from the pathogens, or to chemicals produced when the plant cell wall is attacked. this stimulates the release of signalling molecules that appear to switch on genes in the nucleus. this in turn triggers cellular responses, which producing cellular defensive chemicals, sending alarm signals to unaffected cell to trigger their defences and physically strengthening the cell wall.
• How quickly is callose synthesized after a pathogen attack?

  Within minutes of the attack