Diseases and Fighting them

Vaccination

• Once infected with a microorganism your WBC take a few days to learn how to deal with it
• But by the time they do you can be very ill
• A vaccination involves injecting small amounts of dead/inactive microorganisms
  • This causes the body to produce antibodies against the foreign bodies
    • E.g. MMR vaccine contains weakened virus versions of measles, mumps and rubella
• After a vaccine the body already knows how to deal with a/some microorganisms if a live one infects you
  • This means they can rapidly produce antibodies from existing ones to attack and kill them off
• Some vaccines wear off over time but booster injections can top them up by increasing the levels of antibodies again.
• The speed at which the WBC can kill off the microorganisms gives them no time to damage cells too much or produce a serious amount of toxins.

• Drugs
  • Some relieve systems while others cure the problem
    • Painkillers relieve pain they don't actually tackle the cause of the symptoms just reduce the symptoms
    • Antibiotics (Penicillin) actually kill or prevent the growth of bacteria without killing off body cells.
      • Different antibiotics are for different types of bacteria
      • They can't kill viruses though as viruses reproduce in your own body cells (their hosts) so drugs are hard to make that kill the virus not the body cell.
• Resistant bacteria
  • Bacteria can mutate and somtimes these mutations cause them to become resistant to an antibiotic.
    • So being treated with antibiotics for these so calles 'superbugs' only kills the non-resistant bacteria. This increases the population of the resistant strain, a perfect example of natural slection. E.g. MRSA
    • The rate of development of resistant strains can be slowed by not over-prescribing antibiotics

• Viruses and Bacteria are the 2 main types of Pathogen
  • Bacteria are very small living cells=1/100th of a normal body cell)
  • Bacteria can reproduce quickly in your body
  • They make you feel ill by damaging your cells and producing toxins.
  • Viruses aren't cells and they're much smaller (circa 1/100th of a bacterium)
  • They invade your cells and replicate themselves using the cell's machinary to produce numerous copies of themselves
  • The cell eventully bursts releasing the copies
  • The cell damage makes you feel ill

• Skin, hairs and mucus in your respiratory tract stop a lot of Pathogens getting inside your body
• Cuts=entry point for Pathogens=platelets in the blood (small fragments of cells) help clot the blood quickly sealing entry points.
• Less platelets=slower blood clotting
• If something gets through uter defences the immune system kicks in.
  • IMPORTANT=White blood cells. they traverse the body patrolling for microbes constantly.
    • When they find a microbe they attack three ways
      • Consuming-engulfing foreign bodies and digesting them.
      • Abtibodies-every invading cell has unique molecules called antigens on their surface
      • A foreign antigen=production of proteins called antibodies
        • These lock onto and kill invading cells
        • Antibodies are specific to the type of antigen
      • Antitoxins-produced to counteract toxins produced by invading bacteria

Investigating Antibiotics

• Grown cultures of microorganisms can be used to test drug effectiveness
  • They're grown in a culture medium like agar jelly which contains the carbs, minerals, proteins and vitamins they need for growth.
  • Hot agar jelly gets poured into petri dishes, cools and sets
  • Inoculating loops (metal wire loops) are sterilised and used to transfer microorganisms to the agar jelly (culture medium). Here the microorganisms reproduce and grow.
  • Paper discs soaked in different antibiotics are then placed on the jelly. Antibiotic resistant strains will continue to multiply while the non-resistant will be killed off.
  • Petri dishes, Inoc. loops and culture medium must be sterilised before use. Inoc. loops get passed through a (bunsen burner) flame.
    • Unwanted organisms could get onto the culture medium without sterilisation and mutiply.Affecting the result.
  • Petri dish also needs a lid stopping any air-borne microorganisms contaminating the culture.
    • This should be taped in place/secured somehow.
  • In a lab at school cultures are kept at 25C. Harmful Pathogens likely won't grow at this.
  • In industrial conditions cultures are incubated at higher temps. These grow faster.

Bacteria

• They can mutate to produce new strains
• New strains can be antibiotic resistant and so infections would no longer be cleared by current treatments.
• OR a new strain could an unencountered one so no-one would be immune to it.
• Thus a new strain of bacteria could spread rapidly and cause an epidemic.

Viruses

• Viruses also often mutate making it hard to develop a vaccine that will work for a length of time because changes to their DNA can make their antigens different and so unrecognisable.
• A virus evolving that is both deadly and very infectious=a real problem
  • If this happens precautions could be taken to stop the virus spreading in the first place (quarantine) and vaccines and antiviral drugs could be developed (however it would take a while to get them mass produced.
• In the worst case scenario a Flu Pandemic could cause billions to die all over the world.

Pros of Vaccination

• Vaccines have helped control lots of infectious diseases that were once common in the UK. Smallpox now never occurs and Polio infections have fallen by 99%.
• Herd immunity=vaccines prevent large outbreaks of disease if a large % of the population is vaccinated.
  • This way fewer people will catch the disease (even if not vaccinated) as there are fewer people to pas it on.

Cons

• Vaccines don't always work-sometimes they don't provide immunity
• People sometimes have bad reactions to vaccines but these are very rare e.g. swelling, or sometimes fever/seizures.

Semmelweis

• Used Antiseptics
• Working in Vienna Hospital in the 1840s he noticed women dieing in huge numbers after childbirth from puerperal fever.
• He believed doctors were spreading diseases through unwashed hands.
• He cut the death rate by 10% (from 12 to 2).
  • He did this by getting doctors to wash their hands in an antiseptic solution before entering his ward.
    • The antiseptic solution killed bacteria on their hands but no-one knew of the existence of bacteria and how they caused diseases for another 20 years.
    • Since he couldn't prove why/how his idea worked it was dropped when he left so death rates rose again.
• Now we know basic hygeine is essential to controlling the spread of diseases (though recent reports have found that lack of it in oe hospitals has helped spread MRSA)

Antibiotic Resistance

• • It's becoming more common
  • For the last few decades we could deal with bacterial infections with antibiotics so the death rate from infectious diseases geatly decreased.
  • Overuse of antibiotics has made the problem of antibiotic resistant strains of bacteria even worse by increasing the probability of someone being infected by an anticiotic resistant strain.
• People infected with these strains can't easily get rid of them so may pass on the infection to others.
• So antibiotic resistance=a big problem=drug companies beginning to work on finding an alternative to antibiotics that's effective against these strains.
• Meanwhile 'superbugs' (resistant strains) are becoming more common.