Human Behavior and the Rise of Disease

Plan for Today Last week: How disease shapes society Today: How society shapes disease –Antibiotic resistance –Mad Cow disease

Topic 1: Antibiotic Resistance

First, some questions for you 1.How many of you have ever taken an antibiotic at a time when you were not prescribed to do so by a doctor? 2.How many of you use antibacterial soap? 3.How many of you think it is possible for a disease to become resistant to antibiotics? 4.How many of you think it is possible for a human being to become resistant to antibiotics?

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 doesn’t 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

And…it gets worse 1.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 2.Over time, you can build up crops of antibiotic-resistant bacteria in your body –if you’ve 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

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

Some Handy Hints for You 1.Do use antibiotics when they are prescribed by a doctor 2.Do not use an old antibiotic prescription when you are feeling sick–see a doctor 3.Do avoid antibacterial soap (if possible). All soap kills bacteria by breaking down the cell membrane. 4.If you are a farmer, do not spray your crops with antibiotics (they do this to prevent rot due to bacteria)

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?

Topic 2: Mad Cow Disease A.K.A. Bovine Spongiform Encephalopathy (BSE)

First, a question How many of you eat beef?

Some Background How do you prove that a particular agent causes a particular disease? 1.Prove the agent is present in every instance of the disease 2.Isolate the agent from a diseased individual and grow it independently 3.Use that sample to cause the disease in a healthy individual 4.Recover the agent from that infected individual

Is it this easy? This process is easy with bacteria since they’re relatively big (so we can see them) and they reproduce fast It took scientists longer to find viruses because they’re 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

So there are three options: 1.Keep looking for a different cause for the disease 2.Claim that the cause of the disease is really weird 3.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) don’t work with this disease, so it can’t be a bacterium or virus

How does the infection work? 1.A person ingests an abnormally-shaped prion from contaminated food. 2.The abnormally-shaped prion gets absorbed into the bloodstream and crosses into the nervous system. 3.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. 4.Both abnormal prions then contact and change the shapes of other normal prions in the nerve cell. 5.The nerve cell tries to get rid of the abnormal prions by clumping them together in small sacs 6.Because the nerve cells cannot digest the abnormal prions, they accumulate 7.The sacs of prions grow and engorge the nerve cell, which eventually dies. 8.When the cell dies, the abnormal prions are released to infect other cells. 9.Large, sponge-like holes are left where many cells die. 10.Numerous nerve cell deaths lead to loss of brain function, and the person eventually dies.

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!

It’s all about the cows Normally, cows are herbivores To make beefier cows, big farms often give cattle beef to eat–if the feed beef is contaminated with brain, BSE can be passed to many cows

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

Can humans get Mad Cow Disease? Maybe–was 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)

In sum… Human behavior can significantly impact the rise and development of disease Another big theme as of late: don’t mess with Mother Nature –More on this next time, when we’ll do some background on genetically modified foods