Human Behavior and the Rise of Disease

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Human Behavior and the Rise of Disease
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Plan for Today

• Last week How disease shapes society
• Today How society shapes disease
• Antibiotic resistance
• Mad Cow disease

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Topic 1 Antibiotic Resistance
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First, some questions for you

• How many of you have ever taken an antibiotic at
  a time when you were not prescribed to do so by a
  doctor? 
• How many of you use antibacterial soap? 
• How many of you think it is possible for a
  disease to become resistant to antibiotics?
• How many of you think it is possible for a human
  being to become resistant to antibiotics? 

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How does antibiotic resistance work?

• Resistance to a particular antibiotic can arise
  as a mutation in bacteria
• For example, Streptomycin resistance occurs in
  about 1 out of every 2,500,000,000 e. coli
  bacteria.
• Ordinarily these get cleaned up by the immune
  system.
• If the immune system doesnt get all of them, you
  can have problems.
• First, bacteria will repopulate after most have
  been killed by an antibiotic
• Next, the survivors will include a
  disproportionate number of antibiotic-resistant
  bacteria
• Finally, these antibiotic-resistant bacteria
  reproduce, so the antibiotic-resistant genes will
  be at a much higher frequency in the next
  generation
• Ultimately, antibiotics will be far less
  effective in fighting off this bacterial
  infection if it spreads to others

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Andit gets worse

• You have tons of good bacteria in your body
• For example, e. coli in your digestive tract
  produces vitamin K, which helps with blood
  clotting
• every time you take antibiotics, you kill the
  good and bad bacteria
• Over time, you can build up crops of
  antibiotic-resistant bacteria in your body
• if youve got antibiotic-resistant bacteria, then
  pathogens entering your body could pick up the
  resistance from the bacteria through the exchange
  of plasmid (small pieces of DNA)
• Every time you use antibiotics, you increase the
  chances that your body will contain
  antibiotic-resistant strains of bacteria

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Some of the Results of Antibiotic Resistant
Bacteria

• Almost no one takes penicillin anymore because
  too many bacteria are resistant to it
• This is happening with many common antibiotics
• New antibiotics need to be phased in constantly
• Anyone heard of Cipro before the anthrax scare?
• Pharmaceutical companies keep some drugs in
  reserve for future use, when other antibiotics
  become useless

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Some Handy Hints for You

• Do use antibiotics when they are prescribed by a
  doctor
• Do not use an old antibiotic prescription when
  you are feeling sicksee a doctor
• Do avoid antibacterial soap (if possible). All
  soap kills bacteria by breaking down the cell
  membrane.
• If you are a farmer, do not spray your crops with
  antibiotics (they do this to prevent rot due to
  bacteria)

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And an assignment for next time

• Please find 5 people you know and ask them the
  following questions.  They should not be students
  in the class (though fellow Westminster students
  are acceptable).  Record their answers and we
  will discuss as a group in class next time 
• 1)      How affective are antibiotics at fighting
  colds? 
• 2)      Have you ever taken an antibiotic at a
  time when you were not prescribed to do so by a
  doctor? 
• 3)      Do you use antibacterial soap? 
• 4)      Is it possible for a disease to become
  resistant to antibiotics? 
• 5)      Is it possible for a human being to
  become resistant to antibiotics? 
• 6)      Did you know that many farmers
  (particularly fruit growers) treat their crops
  with antibiotics?  Do you know why they do that?

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Topic 2 Mad Cow DiseaseA.K.A. Bovine
Spongiform Encephalopathy (BSE)
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First, a question

• How many of you eat beef?

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Some Background

• How do you prove that a particular agent causes a
  particular disease?
• Prove the agent is present in every instance of
  the disease
• Isolate the agent from a diseased individual and
  grow it independently
• Use that sample to cause the disease in a healthy
  individual
• Recover the agent from that infected individual

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Is it this easy?

• This process is easy with bacteria since theyre
  relatively big (so we can see them) and they
  reproduce fast
• It took scientists longer to find viruses because
  theyre tiny
• With Mad Cow Disease, the problem is that the
  agent that has been identified (a protein called
  a prion) does not appear to reproduce itself, so
  scientists cannot fully test if it is responsible
  for the disease

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So there are three options

• Keep looking for a different cause for the
  disease
• Claim that the cause of the disease is really
  weird
• Find circumstantial evidence
• Scientists have gone with option 2 and 3
• 2 they believe the prion infects normal healthy
  proteins through an unknown process
• 3 all the ways that we kill normal pathogens
  (cooking, poisoning, radiation, etc) dont work
  with this disease, so it cant be a bacterium or
  virus

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How does the infection work?

• A person ingests an abnormally-shaped prion from
  contaminated food.
• The abnormally-shaped prion gets absorbed into
  the bloodstream and crosses into the nervous
  system.
• The abnormal prion touches a normal prion and
  changes the normal prion's shape into an abnormal
  one, thereby destroying the normal prion's
  original function.
• Both abnormal prions then contact and change the
  shapes of other normal prions in the nerve cell.
• The nerve cell tries to get rid of the abnormal
  prions by clumping them together in small sacs
• Because the nerve cells cannot digest the
  abnormal prions, they accumulate
• The sacs of prions grow and engorge the nerve
  cell, which eventually dies.
• When the cell dies, the abnormal prions are
  released to infect other cells.
• Large, sponge-like holes are left where many
  cells die.
• Numerous nerve cell deaths lead to loss of brain
  function, and the person eventually dies.

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Where did it come from?

• To get BSE, you need brain contact with an
  infected organism
• How does this happen? Through eating brain, of
  course, either as a delicacy or in ground beef!

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Its all about the cows

• Normally, cows are herbivores
• To make beefier cows, big farms often give cattle
  beef to eatif the feed beef is contaminated with
  brain, BSE can be passed to many cows

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An Irony

• So the cattle industry, in order to make money,
  fed cows beef that was unknowingly contaminated
  with cow brain
• As a result, in Britain, millions of cows had to
  be destroyed and people are still afraid to eat
  British beef (this could happen in the U.S. also,
  although there is at this point no evidence for
  BSE in any U.S. cows)
• P.S. Safety checks are now in place in the U.S.
• most meat by-products are prohibited in animal
  feed
• no feed or animals are imported from countries
  with BSE outbreaks
• oddly behaving cows are tested for BSE

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Can humans get Mad Cow Disease?

• Maybewas a rise of BSE in cows and
  Creutzfeldt-Jakob Disease in humans in Britain
  but no definite link found
• C-J Disease symptoms
• Early failing memory, lack of coordination,
  visual disturbances
• Middle pronounced mental deterioration,
  blindness, coma
• End death (usually within 1 year of onset of
  symptoms)

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In sum

• Human behavior can significantly impact the rise
  and development of disease
• Another big theme as of late dont mess with
  Mother Nature
• More on this next time, when well do some
  background on genetically modified foods