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.