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Meet the tapeworm hunters scouring shark guts for these 'beautiful little' parasites

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An eight-year quest to find these bizarre parasites turned up more than 200 new species.

Yorker Izardi is parasitologist Janine Caira’s favorite species of tapeworm. It uses hooks to latch onto its host’s intestines. “So they look kind of vicious, but they're actually pretty awesome.”
Yorker Izardi is parasitologist Janine Caira’s favorite species of tapeworm. It uses hooks to latch onto its host’s intestines. “So they look kind of vicious, but they're actually pretty awesome.”
Image by Janine Caira

Hunting for the tapeworms that infest shark and ray guts has made Kirsten Jensen and Janine Caira pros at dissecting on the fly. The two parasitologists have extracted fish entrails in parking lots, on moving boats, and on hotel room balconies. They have to act quickly, because tapeworms don’t survive for long in the bowels of a dead host. Wait too long and “the worms tend to rot because they’re delicate little creatures,” Caira says. “Tiny, delicate, beautiful little creatures.”

Tapeworms are bizarre parasites that latch onto the lining of animals’ guts — yeah, yours, too — and soak up the nutrients floating by. With no heads and no intestines of their own, these living noodles can stretch from a hundredth of an inch to 100 feet in length. For nearly a decade, Jensen at the University of Kansas and Caira at the University of Connecticut have spearheaded an international effort to inventory all of the tapeworms on Earth. Now, the team has reported on nearly 5,000 species of tapeworm in a massive paper published by the University of Kansas Museum of Natural History, including 215 species that are newly discovered.

The project began as part of a larger push by the National Science Foundation to survey the planet’s biodiversity — particularly for less-loved creatures. It’s important work, because tapeworms are the nightmare versions of canaries in the coal mine. These parasites travel up the food chain as they mature: in the ocean, for instance, tapeworm eggs are slurped up by tiny crustaceans, which then get eaten by bigger creatures, like fish. The tapeworm larvae develop in this new host until a larger animal, like a shark, eats it. And that’s how full-grown tapeworms end up in the guts of sharks. It’s the circle of life. So the presence of adult tapeworms in an ecosystem means that the food chain is healthy and intact (if gross).

This is the part of a tapeworm that latches onto its host’s intestine. This particular tapeworm was discovered in a Giant Shovelnose Ray from Australia.
This is the part of a tapeworm that latches onto its host’s intestine. This particular tapeworm was discovered in a Giant Shovelnose Ray from Australia.
Scanning electron micrograph by Kirsten Jensen

That’s why scientists went looking for the parasites all over the world. Jensen and Caira were in charge of searching for the tapeworms infecting sharks and rays. (Other teams investigated the bowels of birds, mammals, reptiles, and bony fish.) They partnered with local scientists, visited fish markets, and followed fishing boats in 16 different countries, offering to clean fresh catches. That’s how the two scientists found themselves on the backs of scooters racing to a harbor in Vietnam to retrieve the guts of a freshly caught ray. With a baggie of entrails in hand, they skulked back to the hotel room. “You don’t exactly want the hotel to know that you're dissecting on your balcony,” Caira says.

During a break from tapeworm-hunting — there are probably 20,000 different species out there — the two scientists spoke with The Verge about their favorite tapeworms, and how to avoid getting infected.

This interview has been edited for brevity and clarity.

What’s the best tapeworm? Use any criteria.

Seussapex karybares, parasitologist Kirsten Jensen’s favorite species of tapeworm, is named for its resemblance to the Cat in the Hat.
Seussapex karybares, Kirsten Jensen’s favorite species of tapeworm, is named for its resemblance to the Cat in the Hat.
Image by Kirsten Jensen

Kirsten Jensen: The tapeworms that my lab primarily studies have a thing on the apex of their scolex, [the front part of a tapeworm that latches on to the host’s intestines], which makes them look like they’re wearing hats. [That’s] a genus that we named Seussapex. We don't want to get into trouble for not having told Dr. Seuss that we did this, but it’s named after Dr. Seuss because it looks just like a Dr. Seuss character.

Janine Caira: It looks just like the Cat in the Hat's hat. One of the groups of tapeworms that my lab works on has hooks, so they look kind of vicious, but they're actually pretty awesome. It turns out that the hooks are made of several different kinds of protein — some of which may actually be unknown as of yet. The anterior part of the tapeworm, in that case, is divided into two separate regions that function sort of on their own, independent of one another. It pushes the boundary of how bizarre tapeworms are for me. But it also is a really cool-looking tapeworm.

How do people generally contract tapeworms?

KJ: From eating raw or undercooked fish or meat that contains a larval tapeworm. But as soon as it's cooked, any of that fish or meat would be safe to eat in terms of tapeworm infection. Humans cannot contract any of the tapeworms in sharks or stingrays, birds, or certain groups of mammals that are not closely related to us.

JC: We would appreciate if in your article, you could put in big capital letters: “TO AVOID CONTRACTING TAPEWORMS, COOK YOUR FOOD.”

Litobothrium nickoli, found in a pelagic thresher shark from Taiwan.
Litobothrium nickoli, found in a pelagic thresher shark from Taiwan.
Scanning electron micrograph by Kirsten Jensen

Do tapeworms make their hosts starve?

JC: No. It's kind of a fallacy. In the case of that really long tapeworm that does infect humans, it has a super high affinity for vitamin B12, so sometimes it will cause anemia. But for the most part, tapeworms, if they’re in their natural host, they don’t do a lot of damage. Probably because we think the tapeworms for sharks and rays have been there for hundreds of millions years. They’re not helping the host, so it's not a mutualistic association, but they’re not doing a huge amount of damage to the host either.

So is having a pet tapeworm a good way for a healthy person to lose weight?

KJ and JC: No!

JC: Bad idea, bad idea. In the end, it doesn't actually consume that much food. It’s kind of fallacious to think that tapeworms actually out-compete what’s happening in your gut. If anything, [some could] give you a vitamin B12 deficiency and erode the surface of your mucosa a bit. [For a pet,] pick something more like… a chinchilla.

This tapeworm in the genus Paraorygmatobothrium infests pelagic thresher sharks in Taiwan.
This tapeworm in the genus Paraorygmatobothrium infests pelagic thresher sharks in Taiwan.
Scanning electron micrograph by Kirsten Jensen

Is it possible to pull a tapeworm out of your nose? A colleague of mine swears she saw that happen once in first grade.

KJ and JC: No.

JC: There is a fairly large nematode [a type of roundworm] that people can actually get as an infection. In this case, the individuals are separate sexes and the female has been known to wander around the body including coming out the nose while looking for a male. But, that's not a tapeworm.

Are there any foods you’re permanently put off now?

KJ: I can’t not enjoy my sushi, I have to admit.

JC: I find it quite a challenge that I work with people who still eat raw fish.

KJ: I don’t know if I’m a risk taker. If you cut your fish thin enough, you might see it, given a trained eye…

JC: Or you could just cook your food and be fully confident you're not picking up a tapeworm infection! I'm just saying. I’m a big fan of cooked food, and yes, it's because I’m a parasitologist.