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  • Hey smart people, Joe here.

  • What do poke, sushi and sashimi, and all these dishes have in common?

  • They're delicious.

  • They're made with raw fish.

  • And they could all give you parasites.

  • Yep.

  • The ocean is a parasite playground.

  • That warning about raw or undercooked fish at the bottom of every menu?

  • It's there for a reason.

  • At least 15,000 different species of wormy parasites use fish as a host.

  • Raw fish dishes like sashimi are, wellraw.

  • They're never cooked--which means any parasites or parasite eggs in the fish can end up in

  • our tummies.

  • In case you're wondering, let me make this next part extra clear for ya: Parasites are

  • so common in fish, if you've eaten raw fish more than a few times, you've almost definitely

  • eaten a parasite egg.

  • The real question isdid it hatch?

  • [OPEN]

  • Ok, so Anisakis is one of the parasites you could get from eating sashimi.

  • One investigation found that 10% of salmon sushi sampled from Seattle restaurants contained

  • dead Anisakis worms.

  • Now, if that raw fish is treated according to regulations--previously frozen for at least

  • 7 days at -20 degrees C -- then the parasites and the eggs should all be dead.

  • But that means you did still definitely eat them.

  • If the fish isn't frozen correctly or it's eaten fresh, viable worms and eggs can make

  • it into your gut.

  • Like all parasites, these worms live in a carefully evolved life cycle: The eggs are

  • released into the ocean through marine mammal poop, which are then eaten by crustaceans,

  • which are then eaten by fish.

  • When people eat this fish, we interrupt this natural cycle, and the nematode worm larvae

  • can take up residence inside our throat, stomach, or intestinal lining instead.

  • On rare occasions people report feeling a tingling after eating sushi--that's not

  • the wasabi people, it's worms!

  • Well, it's probably wasabi.

  • But it COULD be worms!

  • Of course parasites don't have to be worms, they can come in a ton of forms from microbes

  • to ticks to plants to fungi.

  • Humans have recognized the weirdness of parasites for a long time, from the ancient Greeks and

  • Egyptians to the Chinese.

  • The first written records show up on medical papyruses from ancient Egypt, and we've

  • found parasite eggs in actual 3000 year old mummies.

  • They're even described in the Bible.

  • The 'fiery serpents' mentioned in the Old Testament are thought to be an early description

  • of a painful condition caused by Guinea worms.

  • But back thendoctorsdidn't understand how people actually got parasites.

  • In the 17th century, folks thought parasites just spontaneously generated in the human

  • body because they never saw the worms go in, they only ever saw the worms come outif

  • you know what I'm sayin.

  • Of course now we know parasites don't have to go in as whole worms.

  • You only need to eat their eggs.

  • That's how the life cycle of another ocean parasite goes: Euuuu've gotta be kidding

  • me, I can't say that name.

  • THAT thing resides in salt marshes off the California coast.

  • It gets passed around by three different hosts: Birds poop out the parasite eggs, and the

  • eggs get eaten by horn snails.

  • Then the parasite castrates the snail and reproduces inside it.

  • Then, the parasite swims out of the snail, and into the gills of the unsuspecting California

  • Killifish.

  • It digs through the gills and into the fish's head, where it weaves a little parasite carpet

  • over the little fish's brain.

  • Killifish that are infected with parasites jerk around and swim near the surface of the

  • water, which make birds THIRTY times more likely to snatch that killifish up for a snack

  • than one that isn't infected with parasites.

  • The parasites are promoting their own survivalby getting the fish eaten.

  • Finally, after the fish get munched, the parasites burst out into the birds' guts and the cycle

  • starts all over again.

  • Now, that is the circle of life.

  • Ok, so fish are one thing.

  • But parasites are everywhere, land, sea, even air--they make up as many as half of all animal

  • species.

  • Scientists think more than 200 different forms of parasitism have evolved independently from

  • one another.

  • It's difficult to even estimate the number of parasites on Earth because they can come

  • in so many forms.

  • From the beginning of multicellular life on Earth, parasites have been locked in quiet

  • evolutionary arms races with almost everything living in their environment.

  • Hosts and parasites always trying to stay one step ahead of each other.

  • And here's the thing: Even if you've never gotten sick from eating worm-infected sushi,

  • parasites have impacted your life.

  • Human DNA is full of battle scars from our species' past run-ins with parasites.

  • One of the most famous and nasty parasites out there is Plasmodium vivax, carried by

  • mosquitoes, it's responsible for millions of cases of malaria a year.

  • Today, a whopping 99% of people living in sub-Saharan Africa have a specific type of

  • a protein receptor on their red blood cells that doesn't allow the parasite to gain

  • entry.

  • They evolved a natural malaria parasite defense!

  • We think this change in the genome only took 8000 years to become widespread in that region,

  • meaning it must have been much easier to survive in the environment with that variant of the

  • gene than without it.

  • Parasites cause us harm, so the simple and obvious answer is that getting rid of them

  • is a good thing, but biology is rarely simple and obvious.

  • Preserving parasites could be more important than we realize.

  • Let's return to the California salt marshes and see what happens if we disrupt the parasite

  • balance.

  • Snails that aren't infected reproduce super quickly.

  • This could lead to fewer plants, fewer fish, less for birds to eatby messing with a

  • parasite, we've broken the ecosystem.

  • This is important because parasites are actually at risk--climate change could cause the extinction

  • of one third of them by 2070.

  • Parasites are often gross, but they are critical to keeping balance in ecosystems--and we aren't

  • even close to knowing how diverse the parasite world really is.

  • The conservation of parasites doesn't inspire a warm and fuzzy feeling.

  • But it's just as important to the environment that we save not only the whalesbut also

  • the worms inside their guts.

  • Sushi anyone?

  • Stay curious.

Hey smart people, Joe here.

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    Taka に公開 2021 年 01 月 14 日
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