chapter 12

• communicable diseases are caused by

  infective organisms known as pathogens
• pathogens examples


  bacteria, viruses, fungi and protoctista
• vector

  living or non living factor that transmits a pathogen from one organism to another
• bacteria

  prokaryotic pathogens that do not have a membrane bound nucleus
• bacteria classification

  can be classified by basic shape or by their cell walls
• bacilli

  rod shaped

  
• cocci

  spherical

  
• vibrios

  comma shaped

  
• spirillia


  spiralled

  
• streptobacilli

  chain of bacilli

  
• spirochaetes


  corkscrew

  
• staphylococci


  cluster of cocci

  
• gram positive bacteria

  appear blue under the microscope, strands such as strep and staph for example MRSA
• gram negative bacteria


  appear red under the microscope, strands of E.coli for example salmonella
• antibiotics


  a compound that kills or inhibits the growth of bacteria
• viruses


  non living infectious agents, 50 times smaller than bacterium
• basic structure of viruses

  core of DNA or RNA surrounded by protein, and the genetic material of it overtakes the biochemistry of the host so they are successful pathogens

  
• bacteriophages


  viruses that attack bacteria and use them to replicate, destroying the bacteria at the same time
• what are bacteriophages used for

  identify and treat some diseases and they are important in research, as viruses are now the ultimate parasite
• protoctista


  group of eukaryotic organisms with a wide variety of feeding methods, include single-celled organisms and cells grouped into colonies, small percentage are pathogens and the protists which cause disease are parasitic and may need a vector
• examples of pathogenic protists


  malaria and sleeping sickness, enter the body through polluted water, e.g amoebic dysentery
• fungi

  eukaryotic are often multicellular but yeasts are single celled, cannot photosynthesise and are saphrophytes so they feed on dead matter, or are parasitic, and reproduce as spores so they spread rapidly
• producing toxins that damage hosts

  bacteria produce toxins that poison or damage the host cells, causing disease, some damage the cell membrane and some damage the genetic material to prevent division
• two ways pathogens invade

  1. damaging host tissue directly

  2. produce toxins which damage host tissues
• damaging host tissues directly, viruses

  viruses take over cell metabolism and viral genetic material gets into host DNA, and the virus uses the host to make new viruses then burst out of the cell and spreads
• damaging host tissues directly, protoctista


  some take over cells and break them open as the new generation emerge, but do not take over genetic material, the digest and use the cell contents to reproduce
• damaging host tissues directly, fungi


  digest living cells and destroy them, this combines with the response of the body to the damage caused by the fungus gives symptoms of disease
• why do plant diseases threaten people

  when crop plants fail, people may starve and economies struggle and jobs are lost
• ring rot


  bacterial disease of potatoes, tomatoes, and aubergines caused by gram-positive bacterium, damages leaves, tubers, and fruits and once it infects a field it cannot be used to grow again for at least 2 years

  
• tobacco mosaic virus


  virus affecting tomatoes, peppers and cucumbers, it damages leaves, flowers and fruit, stunting growth and reducing crop yield, resistant strains are available but no cure exists

  
• potato blight


  fungus like protoctist, the hyphae penetrate host cells which destroy leave and tubers, no cure but resistant strains exist, and chemical treatment can reduce risk of infection

  
• black sigatoka


  fungus disease affecting bananas, attacks and destroys the leaves, the hyphae penetrate and digest the cells which turn the leaf black, and it causes a 50% reduction in crop yield, no cure but fungicide can control spread

  
• athlete's foot


  human fungal disease caused by a human form of a ring worm that grows on and digests warm skin between the toes, anti fungal creams are an effective cure
• ring worm


  fungal disease affecting mammals, causing grey-white crusty infectious circular areas of skin, antifungal creams are an effective cure
• malaria

  protoctista plasmodium and spread by anopheles mosquito bites (the vector), plasmodium reproduce in the female mosquito and is passed onto people through eggs, invading RBC's and the liver, no vaccine and limited cures
• tuberculosis (TB)


  bacterial disease caused by mycobacterium and damages lung tissue and suppresses the immune system, TB is curable by antibiotics and preventable by vaccines
• bacterial meningitis


  bacterial infection of the meninges of the brain which can spread to the rest of the body causing blood poisoning and a rapid death, affects 5-19 year olds, antibiotics can cure if caught early, and only some vaccines can protect
• septicaemia

  blood poisoning
• influenza (flu)


  viral infection that kills the ciliated epithelial cells in the gas exchange system, leaving the airway open to secondary infection, deaths occur through 2nd infection such as pneumonia, no cure but vaccines are given to protect against ever changing strains
• strains of influenza (flu)

  there are the A, B and C strains, A are the most virulent and classified by the proteins on their surface, flu viruses mutate regularly, and when there is a major change in surface antigens, it can cause a flu epidemics