Module 7

• Diseases


  Any condition that impairs or interferes with the normal functioning of the body
• Infectious disease


  Caused by the invasion of a pathogen and transmitted from one host to another. Not all infectious diseases are contagious e.g. salmonella
• Contagious disease


  Infectious diseases that spread from person to person
• Pathogen


  Any organism that produces a disease
• Pathogens


  • Fungus that causes ringworm
  • Parasitic worms in intestine
  • Pathogens that live inside organs, tissue or cells
• Cellular pathogens

  Microorganisms composed of cells e.g. bacteria, protozoa. Can reproduce independently. Often treated with antibiotics which target bacterial cells.
• Non-cellular pathogens


  Don't have cells so instead, treatments are more focused on managing symptoms and supporting the immune system
• Vector


  The organism that carries the disease organism
• Antibiotics


  A medicine that inhibits the growth of or destroys microorganisms
• Types of pathogens (from smallest to largest)

  • PRIONS
  • VIRUSES
  • BACTERIA
  • PROTOZOANS
  • FUNGI
  • MACRO-PARASITES
• Prions


  Caused by a misfolded protein produced in the brain. All adult vertebrates have prion proteins however, its abnormal form causes death to brain cells = degeneration of brain tissue. No genetic material, no nucleus, resistant to heat, UV light, chemicals that kill other organisms
• Prions


  • Naturally occurring - Normal and abnormal are the same protein but different shapes
  • Part of the body = immune system does not attack = useless in defence
  • Contains no genetic material
  • Disease is fatal, often called spongiform encephalopathies = forms holes in the brain
• How to catch prion disease

  • Injection or ingestion of brain extracts from individuals with the disease
  • Genetic susceptibility → genes more susceptible to changing into abnormal form, possible to inherit
  • Inadequate sterilisation of instruments in brain surgery = CJD being passed to another
• Treatments for prion disease


  Vaccination and antibiotics are also useless
• Viruses


  Small, have an outer protein coat that encloses genetic material (nucleic acid). Needs a host, cannot reproduce on their own : uses the host's ribosome to replicate themselves, can be crystallised
• Viruses


  • Chicken pox, common cold, HIV → AIDS
• Treatments for viral diseases

  At present, no cure for viral disease. Prevention in the form of vaccination, quarantine or removal or vectors e.g. mosquitoes
• Bacteria


  Prokaryotic organisms. No membrane-bound organelles or nucleus, cell wall, single strand of DNA. Larger than viruses
• Bacteria


  • May respire aerobically or anaerobically → allowed anaerobic forms to live in low oxygen habitats e.g. digestive tracts of animals
  • Releases toxin
• Treatments for bacterial diseases

  Treatment : with antibiotics and infectants. Antibiotics do not kill viruses
• Protozoans


  Single-celled eukaryotes ranging from 2-1000um. Most do not have a cell wall
• Protozoans


  • Only some protozoa are pathogens
  • Most do not cause disease
  • Locomotion (structures to aid mobility) → flagella, cilia, pseudopodia
• Fungi


  Group of eukaryotes with cell wall but no chloroplasts. Some are parasitic (living on a host) or saprophytic (living on dead matter). Mushrooms, yeast, tinea thus can be unicellular or multicellular
• Macro-parasites


  The large parasites e.g. tapeworm that can be seen with the unaided eye
• Macro-parasites


  • Multicellular
  • Two groups: Endoparasites (internal) and Ectoparasites (external)
• Creutzfeldt-Jakob disease (CJD)


  Caused by an abnormal form of prion. Begins at 60s - 70s, memory loss → dementia within a few weeks, death in 6 months, hallucination, difficult balance
• Treatments for CJD


  Currently no cure so treatment aims to relieve symptoms by using antidepressants for anxiety, depression or painkillers
• Ross River fever


  Caused by Alphavirus spread by mosquitoes. Symptoms include itchy rash, headache, lethargy, muscle tenderness, nausea, sore joint
• Treatments for Ross River fever

  Currently no treatments or vaccines to prevent infection. Pain relief e.g. paracetamol are used
• Salmonella


  Causes food poisoning, anaerobic. Symptoms include nausea, diarrhoea, fever. In some cases - fatal
• Treatments for Salmonella


  Often no treatment needed, may need rehydration and antibiotics
• Malaria


  Caused by Plasmodium and spread by mosquitoes. Symptoms include fever, headache, nausea
• Treatments for Malaria


  Antimalarial drugs such as chloroquine. Control involves destroying mosquito vector e.g. insect repellent, mosquito nets
• Tinea


  A group of fungal infections on the skin, reproduce by spores. Symptoms include flaky, reddened areas, itching, stinging, blisters, yellow or white discolouration of nails
• Treatments for Tinea


  Treated with non-prescription antifungal creams or powders. More difficult situations may require antifungal medication in a tablet
• Tapeworm disease (taeniasis)


  Caused by undercooked pork that contains infective live bladder worms, the larvae are released in the human intestine and develop. Symptoms include abdominal pain, nausea, fatigue, loss of appetite or weight loss, pieces of worm in faeces
• Treatments for Tapeworm disease


  Treated with anti-parasite drugs
• Plant defence mechanisms


  • Waxy cuticle acts as a physical battier
  • Thorns or hairs
  • Shedding leaves or branches
  • Cellulose cell wall
  • May excrete phytoalexins - an antibiotic like substance
• Common treatments for plant diseases

  Pesticides, fungicides, bactericides, rotating crops, removing diseased leaves, flowers or fruit, mulch
• How bacteria enter plants

  • Passive entry by moving through natural openings e.g. open stomates, hydathodes, lenticels, nectaries
  • Through abrasion e.g. wounds on leaves, steam, roots
  • Feeding insects introduce the pathogen