4-Infection and response

• pathogens are microorganisms that cause communicable disease:

  • bacteria
  • viruses
  • protists
  • fungi
• pathogens spread through:

  • air
  • contaminated food and water
  • direct contact
• preventing spread of pathogens

  • improved hygiene
  • vaccination
  • killing vectors that carry pathogens
  • isolating/quarantining people who are infected
• virus pathogen can cause:

  • measles
  • HIV
  • TMV
• viruses

  • they enter a cell, use it to make copies of themselves, burst the cell, infect neighbouring cells
  • viruses aren't cells and are not living but are still considered organisms
  • they are 10,000 times smaller than animal or plant cells
  • they can't reproduce by themselves
• virus- measles

  • spread- by an infected person coughing or sneezing (air)
  • symptoms- red rash across body, fever, can be fatal
  • prevent- nearly everyone is vaccinated against it in the UK
• virus- HIV

  • spread- sexual contact, exchange of bodily fluids
  • symptoms- flu-like (fever, aches, tiredness)
  • treat- can't be treated, but antiretroviral drugs can prevent it from replicating
  • damages immune system which becomes so weak it develops AIDS
  • stands for Human Immunodeficiency Virus
• virus- TMV

  • spread- by contact between infected plants, contaminated tools/hands
  • symptoms- discolours patches on leaves causing mosaic pattern, photosynthesis can't take place so can't produce enough sugars for proper growth
  • prevent- wash tools/hands, destroy plant
  • infects the chloroplasts
  • stands for Tobacco Mosaic Virus
  • it affects certain species of plants (tobacco,tomato)
• bacteria pathogen can cause:

  • salmonella
  • gonorrhoea
• bacteria

  • they produce toxins which damage our cells and make us feel ill
  • are prokaryotic so are unicellular
  • are 100 times smaller than animal cells
  • they can reproduce by themselves so replicate very quickly
• bacteria- salmonella

  • spread- eating any contaminated food (chicken, eggs)
  • symptoms- food poisoning, fever, vomiting, diarrhoea, stomach cramps
  • prevent- most chickens have been vaccinated
  • usually passes in a week if person stays hydrated
• bacteria- gonorrhoea

  • spread- sexual contact, unprotected sex
  • symptoms- pain when urinating, thick green/yellow discharge from penis or vagina
  • treat- antibiotic penicillin although lots of gonorrhoea strains have become resistant
  • prevent- avoid unsafe sex, use barrier methods of contraception
  • it is a sexually transmitted disease
• fungi

  • are eukaryotic organisms and can be both unicellular(yeast) and multicellular(mushrooms)
  • multicellular fungi have long thread-like structures called hyphae which spread through the soil which can sometimes spread over plants or penetrate skin which causes disease
  • hyphae can also produce spores that spread easily
• fungi- Rose Black Spot

  • spread- in water, by wind
  • symptoms- purple or black spots form on leaves, as it damages the plant more the leaves will turn yellow and drop off, reduces photosynthesis and therefore growth
  • treat- chop and burn infected leaves, spray with fungicides
  • affects especially roses
• protists

  • are eukaryotic organisms and can be both unicellular and multicellular
  • most are unicellular and classed as parasites
  • they are often transported by vectors between different organisms
• parasites live on or inside another organism
• vectors don't get the disease, just transport it
• protist- malaria

  • spread- transported between hosts by mosquitoes
  • symptoms- recurrent episodes of fevers and headaches, can be fatal
  • treat- antimalarial drugs
  • prevent- kill with insecticides, mosquito nets, mosquito repellent
  • needs a host to survive
• vaccines are dead, weakened or inactive pathogens that can't cause disease but make you immune to that disease because it has the same antigens for the white blood cells to create antibodies against it
• vaccines work against bacteria and viruses
• pros of vaccines:

  • make us immune to diseases
  • control/prevent spread of diseases
  • prevent epidemics (outbreaks)
  • these effects are due to herd immunity
• herd immunity

  • when enough people in population are immune to a pathogen, then the pathogen won't have anyone to spread to and when the host overcomes the disease, the pathogen disappears
  • if a few amount of people do not have the vaccine then they are not likely to catch it as everyone around them is vaccinated
• cons of vaccines (rare):

  • may not work or not grant us full immunity
  • may get bad reactions such as swelling, fever, seizures
• painkillers relieve symptoms of a disease but will not cure the disease, they include aspirin, paracetamol, cough medicine
• antibiotics treat the disease as they directly kill the bacteria or stop it from growing more, they do not treat viruses
• medication is a drug used to prevent, treat or relieve the symptoms of disease
• to reduce antibiotic resistance:

  • patients must take antibiotics for the full prescribed course 
  • doctors should only prescribe antibiotics for serious bacterial infections
• drug development examples:

  • penicillin-penicillium mould contaminated one of Fleming's Petri dishes and killed the surrounding bacteria (antibiotic)
  • aspirin- is a painkiller and lowers fevers, originally found in willow tree
  • digitalis- treats heart failure, originated from foxgloves
• testing drugs:

  • efficacy- how well the drug works
  • toxicity- how harmful the drug is (side effects)
  • dosage- how much should be given
• stages of testing drugs in order: pre-clinical, clinical

  1. human cells or tissue- for efficacy, toxicity
  2. live animals- for dosage, side effects
  3. healthy volunteers- minimum dosage till side effects (optimum dose)
  4. unhealthy volunteers- test optimum dosage
• clinical trials must be fair, so double blind trials are done

  • half of volunteers are given the drug, half are given the placebo
  • only the researchers know who has what, neither the doctor nor the patient know to avoid bias (observing patient more closely)
  • the effects are observed and reported back, then peer-reviewed by other scientists to check tests were fair
  • used for treatment once it has passed testing and is considered safe
• placebo drugs look like the drug that is being tested but are often just a sugar solution