Hi, I’m Aaron Carroll the host of Healthcare Triage. Over on our show, we’re doing a
month-long run on parasites that affect humans. The research for that show has pretty much
ruined sleep for me. It’s taking every bit of willpower I have right now not to scratch
my head right now. We thought we’d share some of the pain with
you. So, fair warning here, if insects or other creepy crawly things make you squeamish
you might want to watch something else. Still with us? Into the breach!
Did you know that bedbugs reproduce by traumatic insemination? After all, why use a female
genital tract for its intended purpose when you have a sharp penis like thing that you
can stab into a female’s abdomen and just ejaculate there? It leaves females with a
gaping wound which can get infected and leave them more likely to die. But who cares? Not
the male bedbugs evidently. Get ready to fear everything, cause that’s
the first of many fascinating (and sometimes horrifying) things I’m going to tell you
about parasites today.
Malaria is caused by the parasite plasmodium. What’s mindblowing about this parasite is
just how ridiculously deadly it is. The WHO has reported that malaria may have killed
close to 200 million people in the 19th century alone. It still kills about 1.2 million people
a year, and most of those people are kids in Africa. There are experts who argue that
malaria has killed about half of all human beings who have ever lived. Really. Regardless,
Malaria kills way more people than almost any other infection, and yet we freak out
over things that are far, far less deadly way more often.
Malaria’s plasmodium isn’t the only horrible parasite mosquitoes gift us with. There’s
also the Wuchereria bancrofti, a roundworm that causes filariasis. Once they get into
your body, they first set up shop in your blood vessels. They’re most commonly found
in vessels in your peripheral circulation which is sort of the outside (as opposed to
deep in your body) from about 10PM to 4AM, meaning they’re making some sort of decisions
on where to hang out in your body at different times of the day. Scientists think this is
adaptive behavior to make them more likely to get into new mosquitoes who might bite
you with the periphery at night. Later in their lives, they move into your lymphatic
system, where they grow and eventually can block it up. Then you get lymphedema, and
eventually elephantiasis, which most commonly affects the arms, legs, breasts, and scrotum
- cause why wouldn’t it?
There are other horrifying roundworms that cause filariasis. Take the Loa Loa worm. The
larva develop in horseflies, which can bite people and infect them. Then the larva travel
through our subcutaneous tissues. At some point, they stop and start to develop into
adults. If you’re lucky, that’ll be in your joints where they cause swelling and
inflammation. If you’re unlucky, they get to your eye. If they do, they swim around
in there, and you can feel them. Swimming. In your eye. If they get big enough, you can
even see them. In your eye. They can live inside you for about 17 years.
Tapeworms come in a number of varieties, but the ones that are more common in the United
States come from beef. If you get one of these numbers, they can grow inside you to about
30 feet in length. The idea of a 30 foot worm is repulsive enough, but the thought of a
thirty foot worm living inside your belly is almost incomprehensible. Even if you get
it treated, can you imagine passing that out into the toilet. Can you?
There’s a flatworm of the genus Ribeiroia that infects amphibians while they are tadpoles.
Once it gets in there, it likes to head to the part of the tadpole that eventually becomes
legs. Then it makes everything go wrong. Frogs infected with these larvae grow extra legs
that are tangled, weird looking, and monstrous. When frogs like this are discovered, we often
fear radiation or toxins, but once again – parasites.
Entamoeba hystolytica is a single cell organism that can infect you for years. You usually
get it from dirty water or unwashed food. Most times, they stay in your gut and cause
local disease. But sometimes they get out and invade other tissues, sometimes causing
abscesses or pockets of infection. At the 1933 Chicago World’s Fair there was an outbreak
from contaminated drinking water that killed infected about a thousand people and killed
58 of them. From aboebas. Single celled organisms.
Although not a true amoeba, Naegleria fowleri made news a couple years ago because it killed
a couple people in the US. How? Ready for this? Neti pots. Yes, those things that some
people use to wash out their sinuses. Turns out two people in Louisiana used tap water
which contained these guys, and they used the opportunity of being in their sinuses
to work their way to the brain and murder human beings. I’ve never understood the
allure of neti pots, to be honest, but the fact that they can let brain eating single
celled organisms into your skull pretty much sealed the deal that I won’t be using them.
Hookworms are the only worms that have teeth. Lucky them, unlucky you. They use these teeth
to latch onto your gut, where they can spend up to 15 years feeding and reproducing. And
I mean REPRODUCING, because the female hookworm can produce 20,000 eggs a day. For like 15
years. When you’re infected, you can have thousands of these guys inside you. They can
cause diarrhea, weight loss, difficulty breathing, and even mental retardation in kids from blood
loss and lack of oxygen to the brain. Their latin name Necator americanus literally means
American murderer.
Guinea worms prey only on humans. You get infected with them when you drink water that’s
infested with their larvae, and they mate inside your GI tracts, and then start to grow.
Eventually, female worms burrow their way out to our skin, where they create incredibly
painful sores by which they can exit the body. They exit very slowly, causing a burning pain
as they do so. There is no treatment for guinea worms. There’s no vaccine. The best we can
do it to wrap the part of the worm that’s exposed around a stick and slowly pull it
out. That can take weeks, and it’s not pleasant at all. One of the only things that soothes
the pain is to submerge the worm and the sore in water, which is, of course, exactly what
you don’t want to do, as it allows the worm to release its larvae and start the cycle
over again. Nut here’s some good news: In 1986, about 3.5 million people were infected
worldwide. But today, thanks to efforts spearheaded by The Carter Center, by April 30 of this
year, there had been only three documented cases in the whole world. It’s
thought that we might eradicate this parasite from the face of the earth soon. Which is
amazing.
Cymothoa exigua is insane. This parasite infects red snappers (the fish) by entering through
the gills. There, it works it way to the bottom of the fish’s tongue, where it latches on
and starts to feed. As it grows, it takes more and more from the tongue, until the tongue
withers away and falls off. At that point, it’s about the size of the old tongue. So
it latches onto the muscles in the fish’s mouth in such a way that the snapper stars
to use it as if it were a tongue. They can also change gender apparently, but that’s
not even interesting when you know the whole tongue thing.
Horsehair worms, thankfully, don’t mess with humans. Which is awesome, because they
basically get their hosts to kill themselves. They mostly infect insects, like grasshoppers.
As larva, they plant themselves on vegetation and form cysts for an unlucky grasshopper
to eat. Inside the insect they do the usual thing of feasting and growing, right up until
they want to mate. They need water for that. So what do they do? They release some compound
that makes the grasshopper want water so badly that it will jump right in, even though grasshoppers
can’t swim. The unlucky hoppers drown, and as they do, the horsehair worms come pouring
out of their anuses, where they can mate and go about their happy lives.
Let’s talk about the Emerald Jewel Wasp, otherwise known as the emerald cockroach wasp.
Why? Cause this wasp totally ruins a poor cockroach’s life. When the female wasp is
ready to reproduce, she finds an unsuspecting cockroach, lands on it, and stings it right
in the thoracic nervous system, which paralyzes its front half. This allows the wasp to deliver
a second surgical sting right in the part of the brain which controls the cockroach's
escape reflex, which basically turning it into a zombie. Then the wasp eats half the
roach’s antennas, why? No one really knows, maybe for sustenance. And then leads the now
zombified roach back to its lair by what remains of its antennas. When it arrives, it lays
an egg on the roach, and leaves the burrow, and then seals it with pebbles to both lock
in the roach and keep other predators out. The roach just lays there like a zombie, alive,
while the larva hatches, eats its way inside, and then consumes the cockroach’s organs
in an order which keeps the roach alive as long as possible so that the larva can form
a cocoon in its body. When it’s done developing it exits the dead roach and goes about its
horrible emerald jewel wasp life.
That’s not the only zombifying parasite. The Dicrocoelium dendriticum is a fluke that
goes through a host of animals. They start their lives in snails, which get infested
with the larva. The snail is smart, though. It walls off the parasite in cysts and excretes
them. But that’s then things go South. Ants eat the cysts, which can contain hundreds
of tiny little flukes. Most hang out and develop and do their usual thing, but one lucky fluke
heads up to the ant’s suboesophageal ganglion, where it takes control of the ant’s nervous
system. Somehow, it waits until it’s nighttime, and then it forces the ant by controlling
its nervous system to leave its home, climb up a blade of grass as high as possible, and
then bite down as hard as it can so it’s stuck there. Why at night? Cause evidently
the sun and heat are harmful to the fluke. If the ant makes it until morning, the fluke
releases its control, and the ant scurries home. But it makes the ant do this every night
up the blade of grass, in the hope that eventually a grazing animal, like a cow, will eat it. Then, they infect
that animal until they start their life cycle all over again.
You made it the whole way? You rock. Thanks for watching mental_floss on YouTube which
is made with the help of all these people. If you haven’t had enough parasite information
you can head over to my channel Healthcare Triage (links in the description down below). We talk about a lot more than just parasites.
You can also catch me writing about much less horrifying stuff over at my blog, The Incidental
Economist, or over at The Upshot at the New York Times (links also down below). If you
have a topic for the List Show that you’d like to see in the future, leave it in the
comments! Try not to get infected by parasites. DFTBA.