3 - Infection and Response

• Pathogens are microorganisms that cause infectious disease 

  • Bateria, virus, protist and fungi

  Bacteria

  • One inside human body, reproduced very rapidly  
  • Release harmful chemicals called toxins- they damage tissues and cause us to feel ill
  • Can be killed by antibiotics

  Viruses

  • Cannot reproduce by these cells, only inside a human cell. 
  • Invades host cells, reproduces inside the, very damaging to the cell, it can cause it to burst open and die 
  • cannot be killed by antibiotics
• • pathogens spread: In the air, water and direct contact 
  • Reduce: basic hygiene: washing hands, clean drinking water, reduce direct contact (condoms), isolated (highly infectious disease- prevents spreading) vaccination 
• Measles 

  • Starts will fever, red skin rash, highly infectious; spreads in droplets when person coughs or sneezes, then passed onto another when they are inhaled 
  • Complicated can develop- damaged to breathing system and brain (can be fatal)
  • Vaccination 
• HIV

  • Flu like illness, virus attacks patient immune system caused it to become damaged, can become so bad it cannot fight off other infections/cancer
  • Patient can easily contract other infections, may even develop cancer- this is AIDS a late stage HIV
  • Antiretroviral drugs stop virus from multiplying, so it does not damage the immune system: stops from developing AIDS- not a cure, must take for the rest of life
  • Transmitted by exchange of fluids: unprotected sexual intercourse, sharing infected needles- blood containing HIV can pass from one needle to another 
• Salmonella

  • Spread through ingesting infected food- prepared unhygienic conditions, the bacteria secrete harmful chemicals called toxins- cause the symptoms of salmonella   
  • Symptoms include fever, abdominal cramps, vomiting and diarrhoea 
  • Sometime find in poultry- but chickens are vaccinated 
• Gonorrhoea

  • Sexually transmitted disease, thick yellow/green discharge, pain from urinating 
  • Was easily treated using antibiotic penicillin, antibiotic resistant strains of bacteria is now common 
  • Stop spread: condom: stops bacteria passing from person to passing, should be tested for gonorrhoea to get antibiotic and prevent spreading 
• Malaria is a communicable disease- spread by a pathogen, it’s a protist 

  • Symptoms: Repeated bouts of fever: can be fatal 

  1. Infected person is bitten by a mosquito, malaria pathogen passes into the mosquito 
  2. Passes the malaria pathogen to another
• Mosquito isa a vector- carries the pathogen from one another

  Stop spread: 

  • stop vector from breeding- they breed in still water, find areas of that water and drain them OR/ Spray areas of still water with insecticide  
  • Prevent the mosquito from biting humans: sleep under mosquito net, the cannot bet though the net and cannot  bite the person, spray it with insecticide so if they land- can get killed 
• Non-specific defence system- to prevent pathogens from entering the human body 

  1. Skin: forms a protective layer, consists of dead cells and is difficult for pathogens to penetrate, sebum- which can kill bacteria

  • damaged skin could allow pathogen to enter to the body- so it scabs over 

  1. Nose- hairs and mucus: trap pathogen before they enter the system
•  Non-Specific Defence Systems

  1. Lungs: if passed through the nose- trachea and bronchi are covered with tiny hairs called cilia. They're covered in mucus which can trap pathogens- they waft the mucus upwards toward the throat where it is swallowed  into the stomach 
  2. Stomach- hydrohalic acids : kills pathogens to stop them from going further down
• White blood cells: 

  Can ingest and destroy pathogens- phagocytosis  

  1. Wbc detects chemicals releases from pathogens and moves toward it  
  2. It then ingests the pathogens 
  3. Wbc uses enzymes to destroy the pathogens 
• Antibodies- protein molecules produced by wbc // lymphocytosis 

  • Release antibodies and they stick to the pathogens- triggers pathogens to be destroyed 
  • Antibodies are specific: if a person catches measelase, will develop antibodies against the measles virus- will only protect measle virus NOT PROTECT other pathogens 
  • Remain in the blood for a long time, can protect incase you get infected with the same pathogen

  Certain types of bacteria can release toxins, these are chemicals wbc can realise antitoxins 

  • Antitoxins stick to toxin molecules and prevent them from damaging cells
• Tobacco Mosaic Virus (TMV)

  • Caused by a virus 
  • Causes leaves to discolour in mosaic pattern 
  • Rate of photosynthesis is reduced: growth of plant is also reduced 
• Rose Black Spot

  • Caused by a fungus 
  • Cause s the leaves to develop purple or black spots- leaves often turn yellow and fall off
  • Rate of photosynthesis falls and this reduces rate of growth 
  • Spread by water or wind
  • Treat: fungicides, remove infected leaves and destroy them 
• vaccinations

  1. Introduce small quantities of dead or inactive forms of a pathogen into the body - Because its dead it cannot lead to the disease
  2. Wbc are stimulated to produce antibodies, at the same time wbc divide by mitosis to produce lots of copies of itself - These copies can stay in blood cells for decades
  3. If the same pathogen enters the body, the wbc can quickly produce the correct antibodies. This prevents infection
• herd immunity

  Important that a large number of people are vaccinated- there are always some people who do not get vaccinated, if enough people are vaccinated it can also protect unvaccinated person

  • The unvaccinated person cannot catch the disease because no one around them can pass the pathogen on
• Antibiotics kill infective bacteria without harming body cells 

  Antibiotic resistance:

  • Overused: bacteria has evolved and are no longer killed by antibiotics
  • Doctor use specific antibiotics to treat specific bacteria  
  • Cannot kill viruses: they live and reproduce inside cells so it is difficult to develop drugs that kill viruses without damaging tissues 
  • Painkillers treat symptoms of disease by relieving pain- do not kill pathogens 
• The plant foxglove was used to extract the heart drug digitalis

  Painkiller aspirin was extracted from willow trees 

  • Drugs were also extracted from microorganisms, Alexander Fleming discovered penicillin in the mould penicillium: removed the tops from some old petri dishes and noticed that the bacteria he had grown were being killed by a mould - penicillin
• testing

  1. Check toxicity of drug whether its safe for human 
  2. Check if its effective (treats the diseases)
  3. Dose size

  Preclinical testing

  • Tested on cells, tissue or live animals 
• clinical testing

  • Carried out on humans, stage 1: very low doses to healthy volunteers check for safety in humans, stage 2: find optimal dose- best dos with fewest side-effects 
  • Placebo- a tablet or inject with no active drug-  patient think they’re going to get better because they believe that they’re going to better 
  • Double blind trial: test group receive active drug, placebo drug looks like test drug bu has no active ingredient- neither patient nor doctor know who’s receiving what, to stop bias incase doctors pay attention to those with actual drug