You've been feeling pretty lonely lately,
so you decide that it's time to get yourself a pet. But you don't want to be too mainstream about
it, so instead of a nice dog or cat you opt for a rat- hey, rats can be cute too you know. You and your rat, Wilbur, quickly become best
of friends, but then one day your best rat buddy picks up an unwanted hitch hiker- a
flea. Then Wilbur's flea decides that it'd like
to take a chomp out of you, and without you even feeling it, the tiny flea has bitten
you and sucked on your blood. For the next three days you and Wilbur continue
your best friendship, going on best friend adventures and solving mysteries together-
then on the fourth day you start to not feel so hot. You chalk it up to all the excitement you
and Wilbur have been sharing lately, but as the symptoms progress you start to feel like
you might have the flu instead. Then suddenly you start growing what look
like huge blisters in your armpits and groin, and the tips of your fingers turn black as
the flesh begins to die! Congratulations, because you've got the bubonic
plague and much like most of Europe back in the 1300s, you're about to be dead. The plague, or black death as it is most commonly
known, has its origins amongst the fleas of rodents from the Central and Western Asian
region of the world. It's believed that climate change during a
period of warming during the medieval ages caused the rodents who carried the infected
fleas to flee the drying up grasslands, while those rodents who didn't believe in climate
change stayed behind and died. Forced into close contact with humanity, the
fleas of these rodents began to feast on our soft, supple human flesh, and in return infected
us with the plague. Historians believe that the plague killed
off many early populations of humans before naturally receding, but what would come to
be known as the Black Death kicked off in earnest early in the 1300s. A secession of natural disasters and lesser
plagues hit south and central asia, which led to widespread famine. Not wanting to be left out of the 'kill all
humans' party, the bubonic plague arrived in 1331, and is believed to have killed 25
million Chinese people before it finally reached Constantinople in 1347. Mongol raids and travelers along the famous
silk road are believed to have pushed the disease further and further west, but it wasn't
until Genoese traders brought plague-infected fleas into the port city of Kaffa in Crimea
in 1347 that the bubonic plague went mainstream. Pretty soon the black death, as it was known
by then, was all the rage amongst Europeans, and by 1351 it had reached as far west as
Spain and as far north as Russia. Before the black death went out of style,
it had killed between 75 to 200 million people, and it's believed that it took the world 200
years to recover the numbers lost to the disease. In the wake of the plague, zealous persecution
of various scapegoats blamed for the outbreak led to the deaths of many thousands more,
including Jews, friars, foreigners, beggars, pilgrims, lepers, gypsies, and people who
get to the front of the line at Starbucks and have to check the menu because they still
aren't sure what to order. The plague had had such a good time in Europe
though that it revisited the continent intermittently throughout the 14th and 17th centuries, causing
many hundreds of thousands of additional deaths. In 1771 the Plague hit Moscow and killed between
50,000 and 100,000 people, or as much as 33% of the city's population. A hundred years before that the plague killed
100,000 in London. Like adventurous European university students
though the plague went global, and between 1500 and 1850 the plague was present in at
least one location throughout the entire Islamic world. So you've gone and gotten yourself infected
with the Black Death- because maybe modern diseases are just too trendy for you- why
is this the worst thing that could ever happen to you? Well, first, could it happen to you? The answer to that question is no, humanity
has long since overcome the terrible affliction known as the Black Death and is safe from
the ravages that once killed hundreds of millions of people. Just kidding, you can totally get the Black
Death today, and if you think you're safe in your First World life because surely it's
only a disease that strikes at the most remote, poorest regions of the world, you may want
to think again. As of 1900 the Black Death had made its way
to the United States, when an epidemic struck San Francisco and lasted until 1904, then
quickly made a comeback throughout 1907 and 1908. While that was over a hundred years ago and
we have developed many drugs and treatments for the plague, just in October of 2017 the
deadliest outbreak in modern times hit Madagascar and killed 170 people while infecting thousands
more. But that's in an island off the coast of Africa,
and San Francisco was over a hundred years in the past, surely we're safe today. Once more, no, absolutely not, and in fact
the western United States is one of the largest geographic areas where the plague is reported
in wild animals and livestock alike- so keep that in mind next time you decide to hit up
a petting zoo. But what about the plague is so terrible? Well, before we tell you we'll warn you to
go ahead and finish eating if you were eating, or to cancel any lunch or dinner plans you
may have had coming up, because we doubt you'll have the appetite after this episode. It starts off with a flea bite, or perhaps
a bite from an infected rodent, and then suddenly your body is host to a nasty little bacteria
called Yersinia pestis. Our bodies however have had plenty of exposure
to the plague by now, seeing as Yersinia pestis' favorite historical past time was to murder
all humans, and so the body has learned to very quickly recognize Y. pestis from a unique
molecule in its outer membrane. Unfortunately, some time in the past Y. pestis
caught on to this fact and now when it detects a temperature of about 98.6 degrees (37 Celsius),
the bacteria figures that it's inside a warm blooded mammal. This triggers Y. pestis to modify the structure
of the give-away molecule, effectively blinding your body's immune system to its real identity. With your immune system fooled, Y pestis makes
a mad dash for your lymph nodes- which seems like an odd choice for an invading bacteria
because your body's lymph nodes are basically immune system fortresses, and constantly looking
for foreign invaders to wipe out. For any other bacteria this would pretty much
be a suicide run, but Y pestis is basically the Seal Team Six of bacteria. Your body immediately tries to stop the bacteria
with white blood cells, the cells responsible for immune system response, but Y pestis responds
by shooting these responding cells with an appendage that injects toxins directly inside
the cell's membrane, destroying it. After owning the crap out of your immune system,
Y pestis needs to recover by getting a hold of some iron, and luckily for it your body
is chock full of it. Unfortunately for the bacteria, all that precious
iron in your body is wrapped up in hemoglobin and other proteins- or unfortunate for you
really, because if you've learned anything by now it's that Y pestis gets what it wants
when it wants it. While it holds the fort down in your lymph
node, each bacteria releases a molecule called yersiniabactin which has a very high affinity
for iron. The molecules cruise through your blood system
on the lookout for a specific iron-rich protein in your body called transferrin. Once the molecules find some transferrin they
literally rip the iron away from the protein, destroying it in the process, and bringing
it back home to Y pestis. By now the plague is happily making your lymph
nodes into its new home, kicking up its feet and replicating out of control thanks to a
rich supply of iron. At this point you're definitely feeling under
the weather, with general flu-like symptoms, but if you're like most people you ignore
these symptoms and push through without going to the doctor. In this case your failure to get checked out
will be fatal, as with modern medicine the plague can be cured in over 90% of cases if
caught early. If not, well your odds aren't very good at
all. At this point your lymph nodes begin swelling
up, which create the iconic “buboes” so characteristic of the bubonic plague. These look like very large blisters and can
appear on the arms, leg, groin, and arm-pits, can grow to be as big as an apple! By now you're going to have a really high
fever and might even be vomiting blood, and if any of those buboes burst open you'll be
oozing pus and other disgusting fluids from the open sores. This can be extremely dangerous, because buboes
that are burst open can lead to secondary infections from other bacteria, but luckily
for you you'll be dead long before any of these infections can properly set in. Gangrene can also set into extremities, and
fingers and toes can blacken as the flesh dies and eventually fall off. Incredibly, it's not the plague that kills
you though, but rather your own body that does the deed. With Y pestis bacteria throughout your blood
stream your immune system totally loses its cool and triggers a condition known as septic
shock, causing your blood vessels to leak which lowers blood volume, clotting, and eventually,
organ failure. Luckily though modern medicine is able to
cure plague if caught quickly enough, though many doctors today worry that the plague will
very quickly begin to develop an immunity to most of the drugs we use against it. This has prompted a renewal of the arms race
that has lasted for millennia between man and bacteria, and it's hoped that new vaccines
and antibodies can be developed to stop the plague before it kicks off another world tour
and leaves millions dead in its wake. Where in the past the remote nature of most
human villages and cities made it difficult for the plague to be transmitted and thus
limited its lethality, today's hyperconnected world would let the plague travel around the
world in as little as a day, and an outbreak that started far overseas could be in your
neighborhood by that evening. In fact, it might already be there, and we
might all be on the verge of the next huge outbreak. Do you think we could survive another outbreak
of the plague? Let us know in the comments! Also, check out the brand new channel called“I
Am.” Real stories come to life as they’re told
from the perspective of the people who lived it. Check out “I Am a Plague Doctor” right
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