6 Parasites That Live INSIDE Cells


[intro] What do you think of when you hear the word
parasite? Maybe blood-sucking leeches or swarms of mosquitoes spring to mind — or maybe your dog had a tapeworm one time. A parasite is any living thing that lives
and gets its food at the expense of another, generally on or in its host. And some of them cause some nasty diseases. But some parasites take that in thing to extremes. They don’t just live attached to another
organism, or hide out in its gut. No, they live inside their host’s very cells. Some of them are huge problems for humans, while others are mere curiosities. And while some are bacteria, or other tiny
organisms, others aren’t what you’d expect at all. Here are 6 such tiny parasites, and how they
do it. First up on our list is a group of microbes
belonging to the genus Plasmodium, parasites that cause malaria in humans. As you may have heard, this parasite kills a lot of people. Plasmodium has a complicated life cycle that
takes it from a mosquito’s gut to its saliva to a human liver to the bloodstream. And that last part is what causes malaria
symptoms. After multiplying in the liver for a while, the parasite bursts out and attacks red blood
cells. Incidentally, a single liver cell can produce
thousands of Plasmodium cells — and a red blood cell can breed a few dozen. Once it’s inside a red blood cell — and this is what makes malaria so tricky to
treat — Plasmodium starts rearranging the furniture. This includes sticking new proteins on the
surface of the cell, and creating tiny knobs that cause infected
red blood cells to stick to blood vessel walls. That prevents them from flowing through the
bloodstream and getting thrown out by the spleen, which
normally identifies defective blood cells. The infected blood cell can also clump together
with uninfected red blood cells, disguising itself among the healthy cells
in something called a rosette. And those clumps can block traffic. If these sticky, nonfunctioning red blood
cells bunch up in the wrong spot in a blood vessel, they can deprive that area of oxygen. And you definitely don’t want that to happen
in the brain or other vital organs. But the ability to make those little proteins
that stick out of the cell is also what makes malaria so hard to detect
by our immune systems. Plasmodium has about 60 genes that can code
for a variety of these proteins. And research published in 2017 reported that
different patterns of those genes show up in different patients — and that likely hinders our ability to develop
immunity. There is a ton of research ongoing, but malaria still kills hundreds of thousands
of people every year, mainly in Africa. So there’s still work to do. Number two on our list is Rickettsia, a group of tiny bacterial parasites transmitted
to humans by creepy crawlies like fleas and ticks. And you’ve likely heard about the diseases
these parasites cause — sicknesses like Rocky Mountain Spotted Fever
or typhus. These are some of the nastier, more deadly parasitic infections out there. The U.S. Centers for Disease Control have
even listed them as potential tools for bioterrorism. Now, if a tick with Rickettsia bites you, the bacteria get into your bloodstream. But unlike Plasmodium, they don’t target
red blood cells. Rather, Rickettsia tends to live in the cells
lining your blood vessels. The infection causes various problems with
the circulatory system and widespread inflammation. And if it gets severe enough, the patient can face pneumonia, swelling in
the lungs, or kidney failure. Life-threatening stuff. Researchers are currently trying to understand
how these bacteria can get into our cells so easily and of course, how to prevent them from doing
so. A 2015 paper found that proteins on the surface
of Rickettsia cells can actually induce host cells to grab them
and pull them in. Such entry mechanisms aren’t exclusive to
Rickettsia, but we’re interested in learning about them
so we can use that in preventing these dangerous diseases. We can treat Rickettsia infections with antibiotics. But prevention is always better. So be careful out there if you’re hiking
through tick country. Another one of those human-infecting parasites
is Legionella pneumophila, the bacterium behind Legionnaires’ disease
and Pontiac fever. As the name pneumophila implies, this type of bacteria tends to attack the
lungs. And it can cause pneumonia, though this ranges from the fatal kind to
much milder, so-called “walking” pneumonia. Luckily, our immune systems can detect Legionella and send white blood cells to the infected
lung. Plus, most patients respond well to antibiotics. Legionella doesn’t rely on bugs to spread
it, like our first two parasites. Instead, it lives in water — places like stagnant freshwater ponds, plumbing
systems, or stale hot tubs. Legionella has a particularly nasty feature
where it’s resistant to chlorine and heat, our usual methods of sterilizing water. It does need a host to reproduce, but that can come in the form of amoebas sharing
the water with it. And it spreads when people breathe in tiny
water droplets that harbor the bacteria. That could mean anything from an outdoor mister
to an indoor humidifier. The important thing is that you inhale this
water, not drink it. Once in your system, Legionella sticks to its host cell and triggers
the cells to take it up. But it’s less picky than our first two examples
about what kind of cells it infects. And that means it probably has multiple ways
of getting in. Lung cells, in particular, engulf the bacterium
in a compartment where it would normally be destroyed. But somehow, the bacterium keeps the destruction
part from ever happening, and lives there quite happily instead. Meaning until we work out better strategies
for keeping Legionella out of our water, it’s going to keep finding ways to call
our lung cells home. Number four on our list is one of the least
dangerous but most common sexually transmitted infections, Chlamydia trachomatis, or affectionately,
just chlamydia. This parasite spreads very efficiently. It’s the most commonly reported bacterial
STI in the U.S., though many people who have it don’t show
symptoms. Chlamydia is a bit of an oddball in that it’s
a lot less independent than some other parasites. They can’t swim or move on their own, and they lack the ability to produce their
own energy, so they depend on their host cell for just
about every vital function. So the chlamydia bacterium floats around in
an inert form until it attaches to a host cell. Then the host cell wraps up the invader in
a little package called an inclusion, similar to if the cell were trying to destroy
it. Cells have these bodies called lysosomes that
are full of destructive enzymes. Now, usually, we’d expect the little intracellular
inclusion bundle to fuse with a lysosome and let those enzymes disintegrate the invader. And if the host detects something really bad
happening, it can even destroy itself along with the
parasite in the process. Chlamydia not only avoids destruction, but manipulates its host cell to hijack its
energy sources. They do that by using a variety of proteins
to communicate with the host from inside their cosy little inclusions. After the bacterium establishes itself in
the inclusion, it starts replicating and matures, eventually
bursting out from the host cell to start the process over again. From there, chlamydia spreads to new people
through a few different methods, including sexual activity or childbirth. Luckily, chlamydia is pretty easy to cure
with a round of antibiotics. Either way, if you’re sexually active, make
sure you’re routinely getting tested. Next up is microsporidians, an entire phylum
of single-celled organisms. And they’re exactly what the name implies
— parasites with tiny spores that they use to
invade host cells. But these aren’t bacteria — current research
suggests they’re either a type of fungus, or something closely related to fungus. We’re not sure! Now, most humans that contract a microsporidian
don’t show any symptoms — though not in all cases. And they tend to show up more frequently in
patients with compromised immune systems, like folks with HIV or who are undergoing
radiation therapy. And because this is a big and diverse group
of parasites, an infection can cause different symptoms
depending on the type of microsporidian and what body part it infects. Which includes the gut, lungs, and eyes, to
name a few. Lovely. And they have a really fun way of getting
into cells. When a spore encounters a favorable environment,
it starts to germinate. Then it grows a tiny harpoon called a polar
tubule, which it uses to spear the unfortunate host
cell. It uses the polar tubule to inject reproductive
material, which then goes on to eventually develop into
a whole bunch of mature spores — which burst out of the host cell and start
the process over again. Microsporidians don’t limit themselves to
humans. They can live in all sorts of cell types in
a bunch of different kinds of animals, as well as other organisms. Which means contact with other animals is
one way these things might spread — but so might person-to-person contact, inhalation,
ingestion, and direct contact with your eyes. We actually don’t understand how it’s
transmitted all that well. Basically, these things are everywhere. Plus, you might have one right now and not
know it. Cool. Terrifying. Luckily, they usually aren’t too harmful. Finally, we just couldn’t leave out the
last parasite on our list, Polypodium. Unlike the other parasites on our list, this
one wants nothing to do with humans. It exclusively infects the egg cells of sturgeons
and paddlefish. We saved the best for last, though, because
these parasites aren’t bacteria or single-celled organisms — scientists think they’re related to jellyfish. Polypodium live in the fishes’ egg cells
for years before bursting out when the fish spawns, which then destroys that egg cell. What a bummer for that fish. They grow all those egg cells only to realize
they’ve been hosting Polypodium. Scientists have had a hard time classifying
Polypodium, but they’re fairly confident it’s a cnidarian
— belonging to the same group as jellyfish. They make that call partly because it has
those trademark stingers, or nematocysts. While they can get around in freshwater with
no problem, what’s peculiar is how these critters grow
up, which is also what makes them parasites. The free-living parents appear to deposit
the next generation of parasites on the skin of their fishy hosts. But exactly how they get into the eggs of
the fish is still kind of a mystery. When they first show up, they look like a
tiny cell with two nuclei, one bigger than the other. But then that smaller nucleus surrounds itself
with some more cellular material and becomes a sort of cell within a cell. We’re still inside of a fish egg, here. Meaning we have a cell within a cell within
a cell. The innermost Polypodium cell replicates into
a more developed larva. The outer cell serves to protect it. At this point, the larva is a long, slender
organism with a bunch of tentacles tucked inside its body. When it’s ready, the polypodium turns itself
inside out, exposing its tentacles, bursts out of the
host cell, and swims out into open water. Best of all, that baby Polypodium fragments
into multiple free-living adults. Meaning this thing takes turns reproducing
asexually, and doing its best Alien impression in fish
eggs. At this point, the adult Polypodium lives
on its own and continues to develop its sex organs until it’s ready to parasitize another fish
— starting the process all over. You might be reasonably horrified of these
guys by now. But you’re not a sturgeon, so you’re fine. These six examples are just a few of the multitude
of parasites who see the insides of other creatures’
cells as free real estate. Some can cause intense human disease while
some only infect specific fish eggs. Either way, a better understanding of how
these parasites live will give us greater insight into how to prevent
disease and improve life for everyone. And while we’re talking about tiny things, we want to give a shout-out to our new sister
channel produced by Complexly: Journey to the Microcosmos. Journey to the Microcosmos is all about bringing
you closer to the world of very, very small things. All the incredible microscopic footage is
provided by James Weiss. Pair that with meditative narration and music
by Hank Green and Andrew Huang, respectively, and you’ve got what we like
to think is the most relaxing educational channel… ever. Check it out at the link in the description. And thanks for watching! [outro]

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100 thoughts on “6 Parasites That Live INSIDE Cells

  1. "Affectionately known as Chlamydia"?! Maybe "commonly known as…" but I doubt anyone has an affection for it!
    V interesting otherwise 🙂

  2. So lets just take one of these and modify it heavily to affect specific neurons… and we’ve got ourselves a zombie apocalypse, gentlemen

  3. Research shows that people with sickle-cell anemia have high resistance to malaria than people with normal red blood cells, meaning it may have evolved as a way for humans to combat the disease.

  4. what's about the Mitochondria….. it has it's own DNA it's self replicated why can't we consider it as an intracellular parasite

  5. Parasites are wonderful and magnificent . They are marvels of evolutionary and biological engineering . We should appreciate them more. That's not to say that I like to get parasites . They should not be hated so much

  6. I look forward to seeing Olivia smile, but was rather disturbed by her enthusiastic beaming while describing the last two creatures!

  7. That nose piercing is really triggers an impulse, to hold a tissue to her nose and tell her to blow, hard…..🌡💧🧸

  8. Interesting stuff, but please try to not speak the first part of all normal sentences as questions. It would make your videos more pleasant to watch.

  9. Been subscribed to the micro channel since it came out, it's so great and perfect for me. I have a USB microscope I use to look at that type of stuff but I could never capture stuff as good as what they do on that channel so it's great and they obviously have a far better microscope than me, shows me what I might be able to see if I pay a bit more for the microscope next time.

  10. I'd almost trade my uniquely evolved brain for a uniquely evolved ability to live in and eat caviar all day. I only have this brain so I can do lots of sex, food, and computer games. I think the polypodium has the advantage on two of those activities.

  11. By your initial defintion, My Dog is the parasite. Lil Bastard! I think I'll keep him anyway. He's been my lil'buddy for ten years. I can help him through the next year or two. I owe him that.

  12. if you were to take some microsporidian and mix with with some of those jellyfish monsters with a touch of plasmodium and size it up a bit and you have what is basically an all in one facehugger + Xenomorph right there.

  13. This was a bad definition of parasite. It would include all infections and most predators. Although I must admit I don’t think I’ve ever seen a legitimately good definition.

  14. I’ve got parasites in my eye: toxoplasmosis. Usually it doesn’t cause any problems and many people have these parasites in them. Unfortunately for me, it causes dangerous eye infections.

  15. Friend of mine in Africa told me recently he ‘d been there that long he ONLY got Malaria about 3 times a year, just like a local?

  16. She is so smart. I have so much respect for smart women. I just wish she appeared to enjoy doing these videos. You go girl and smile once in a while. 🙂

  17. With advancements in nanotechnology, I think that one day we'll be able to develop machines that kill these parasites before they can penetrate the cellular wall.

    It'll likely be mankind's destiny to become cyborgs.

  18. Most of these aren't scientifically labelled as parasites. Except for the last one they're all either bacteria, viruses or fungi.

  19. I was interested in your new sister channel- until you described Hank Green as one of the ‘soothing’ meditative narrators — honestly that would be like if Gilbert Gottfried did a guided meditation….

  20. In human terms, traffic wardens.
    And from your description that fits.
    Unless members of society trying to penalize, tax car drivers.

  21. Is there a scientific term for organisms that use other organisms as their home? To be clear, I mean a term that encompasses tapeworms AND gut bacteria, but NOT Mosquitoes or Leeches, as the latter two do not use their mark as a shelter

  22. I was so sad when I clicked on journey to the microcosmos when it first started because there were only like 4 videos. They're so calming and the microscope footage is mind blowing

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