Blogs / The Loom

I’ve been quietly watching scientists flip out about Sarah Palin’s recent scoff about the US funding research on fruit flies in Paris–even Christopher Hitchens is now championing those fine insects today in Slate. But, thanks to a little grant-digging by PZ Myers, I discover that, in fact, all this brouhaha comes down to those dear friends of this blog, parasites. Frankly, if you wait long enough, everything comes down to parasites.

A lot of people thought at first that Palin was dismissing basic research on Drosophila melanogaster, which has yielded lots of profound insights about human biology. Palin herself hasn’t cleared up the issue, but on further reflection, the consensus is that she was complaining about research on the olive fruit fly. That insect is a nasty crop pest in the US. It’s also a pest in Europe, where people have been studying ways to control it–hence the need for funding research there.

So–how do they plan to control these pests? By unleashing a vicious, brutal death on their babies! (Apologies to any insect-rights people out there…)

Pests often become pests by getting shipped to new places where they can thrive without all the parasites and pathogens that kept them in check back home. So a promising way to rein them in is to go back to where they were evolved, and find some really nasty parasites that evolved with them. Happily, scientists have found a wasp in Africa, where the olive fruit flies came from, that appears to be specialized to lay their eggs only in the larvae of the flies. The wasps then drink up the larvae’s bodily fluids and crawl out, leaving behind the dried up corpse of their host. So the scientists have shipped the wasps to California and done a lot of testing on the them (you have to make sure they won’t go off and start killing harmless native insects). Their goal is to shower the wasps across the olive fields of America.

This may seem outlandish, but it’s actually a fairly well-developed technique for controlling pests. In my book Parasite Rex, I describe a devastating outbreak that threatened Africa’s cassava plant–a staple for millions of people across the continent. The cassava were being wiped out by mealybugs from South America. In the late 1980s, entomologist Hans Herren and his colleagues found a South American wasp and brought it to Nigeria. Then he had to figure out how to get the wasps to their hosts.

The wasps were put to sleep with carbon dioxide and then lodged in cylinders of foam rubber, 250 in each one, which were loaded into a magazine that had been custom-built for Herren at an Austrian camera factory. As the pilot passed over a field, Herren intended for him to be able to drop the wasps precisely. “It was like in fighter aircrafts. You know when to drop the bomb by looking at the crosshairs. We tried this over a swimming pool in Ibadan. We’d fly over and drop the wasps. At 180 miles per hour, we were able to get them in there.”

Once Herren figured out how to drop his parasitic payload precisely, he started showing millions of wasps on African farms. After a few years, Herren had driven down the mealybugs to tiny numbers.

So please, my fellow Americans, think kindly on parasites this election year. If handled right, they can save your dinner.

[Image Source]

Remember that couple you knew, the ones who went out on a date and instantly fell in love, who had been together for years and seemed as happy together as the day they met, the ones who gave you hope that you might find your own true love, the ones who made you feel that there was joy to be found in the world? And remember how one day they suddenly called the whole thing off and pretty soon were seeing other people, leaving you confused and reeling?

I’ve been having the same experience with blood flukes.

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Conservation Magazine is a snazzy publication from the Society of Conservation Biology that sports some great writers and great graphics. I was pleased to be asked to contribute a piece about some of my favorite living things–parasites. In particular, I look at new research that shows just how integral parasites are to the well-being of ecosystems. It’s just come out in the latest issue. Check it out.

Martijn ter Haar, a person from the Netherlands I’ve never met, clearly knows what sort of movies I like to watch. The ones with big parasitic worms crawling around inside a sealed box of fish at the supermarket. Warning: Safe for work, not safe for lunch.

This bad boy is Anisakis, a worm that would much rather be off in the sea than in your gut. Its eggs float through alll the world’s oceans until they’re scarfed up by a crustacean, inside of which they mature into a new larval stage. Their next host is the fish that eats the crustacean–they escape from its gut and drill into its muscle. Finally, the fish is eaten by a dolphin or a seal, whereupon the worm becomes an adult and lives  harmlessly and happily, churning out eggs that the predators kindly squirt out with their poop. In other words, the good life.

But if some thoughtless fisherman trawls up an Anisakis-infected fish, and you end up eating that fish raw–as sushi or herring–or without cooking it thoroughly, the parasite is doomed. Inside a human host it will die–often without the host even knowing what happened. But sometimes things get a little nasty for the host, too. You may feel a tingle in your throat and cough the worms up. Or you may feel like your appendix just popped. What’s happening is that the poor confused Anisakis is drilling its way out of the gut and wandering around the abdominal cavity. Your immune system may go wild over this visitor and launch a frenzied allergic reaction. Even when there’s no worm crawling around in the fish, you can get an allergic reaction–a few loose proteins left behind are enough. If Anisakis makes you sick, a doctor may have to go in and fish the critter out (as seen in this even more disgusting video from Dr. Peter Kelsey of Harvard).

Out in the ocean, by contrast, Anisakis doesn’t do much harm to its hosts, and they don’t harm it. It’s a relationship fine-tuned by millions of years of coevolution. And when Anisakis populations drop, it’s a sign that the entire food web is not well–thanks to overfishing or pollution. Obviously nobody wants to get to be close friends with Anisakis (note: don’t eat sushi out of the back of a truck). But how about a little sympathy for the ocean-wandering worm trapped in the supermarket?

[Update:  A commenter asks, “What is the actual rate of ‘things getting a little nasty’ for humans”? Severe cases of Anisakiosis are rare, as detailed here. But in Madrid, where people eat a lot of raw fish, 12% of people test positive to exposure–either to the worm or to its proteins.]

 [Image from Dr. Simonetta Mattiucci’s web page]

Mark Siddall, leech master, gets Neil de Grasse Tyson into shorty-shorts and then into a leech-infected Connecticut pond. Even manages to dispense some natural history along the way on leech family values…It’s a teaser for a piece on leeches on NOVA Science Now, which you can watch in its entirety here.

If I wasn’t so swamped this week by deadlines and hosting birthday parties, I’d be rambling on and on about a great new study that suggests parasites make up a huge chunk of ecosystems, simply by sheer weight. I’ll have more to say in the not too distant future, but in the meantime, check out this post at Not Exactly Rocket Science or listen to a good segment on National Public Radio that also includes some important caveats from outside researchers. If you want some back story, you can read this piece I published about the ecological impacts of parasites in Discover some years ago, adapted from my ode to the monsters within, Parasite Rex.

Like a parasite addressing its host, I gave a symposium talk a couple weeks ago at the annual meeting of the American Society of Parasitologists. When I arrived at the meeting, I listened to a number of parasitologists bemoan the lack of interest in parasites among the public. In my talk, I explained why they were wrong.

People are fascinated and obsessed with parasites, and once you’ve captivated their imagination with tales of zombifying wasps and such, you can plunge into some big concepts that apply across biology–concepts that might be hard to get people interested in if you were talking about spliceosomes or metapopulations. In fact, some people may even become parasitologists as a result. (The organizer of the symposium, Carrie Fyler, had such an awakening, she confessed in her introduction, after reading my book Parasite Rex.)

The fascination with parasites starts in childhood. That was my experience as a kid, and my own children are always demanding more information on germs and ticks and the rest. I’ve spoken to high school students about parasites, and–miraculously–I’ve kept them awake the whole time. So it’s my hunch that there are a lot of kids out there who are going to dig a new game on the market called Parasites Unleashed.

Full disclosure: Parasites Unleashed is the brainchild of husband-and-wife team James Cambias and Diane Kelly–Cambias writes science fiction, and Kelly is a biologist. I got to know Kelly years ago when I was writing a lot about biomechanics. Kelly has done some remarkable work on the biomechanics of penises (turtle penises and such, not human ones)–check out this write-up from PZ Myers at Pharyngula. It’s probably not too surprising that Kelly has a great sense of humor and is not at all precious about science. She digs it, and she wants others too as well. She and James started up a company called Zygote Games, and Parasites Unleashed is one of their first games to hit the market.

In an age of Wii and massively multi-player games, Parasites Unleashed is refreshingly low-tech. It’s a deck of cards and a couple pages of straightforward rules. You are a parasite in the game, and the object is to use the cards your dealt or pick up from the deck to complete a successful life cycle. A life cycle must include a HATCH! card and a MATE! card. And these two cards must be flanked by other cards that take you from host to host. (Making the game more challenging is the fact that each card has a colored stripe on each end; every card in a cycle must match its neighboring card, like dominoes.) You can also use special cards to speed your own progress or slow down your opponents.

What makes the game particularly fun is the ways you get from one host to another. Crawl into wound. Leave host in dung. Bore through gut. Wait for host to die. And, as the cards explain, these are all strategies used by real parasites. Likewise, the special cards deliver real science too. If you get a “Immune System” card, you can remove a host card from the end of an opponent’s life cycle and discard it. The cards have bright, engaging illustrations by artist Fred Zinn, and the instructions also have a good summary of the natural history of parasites.

Parasites Unleashed may or may not make your kid into a parasitologist,  but it will definitely turn an obsession with the gross into a teachable moment.

I’m going to be posting my blogroll to my new digs as soon as I get the chance. And to that list I will be adding BdellaNea. It’s the work of Mark Siddall, a scientist at the American Museum of Natural History who specializes in leeches.

I wrote about Mark in this 2006 article for the New York Times, and last weekend at the meeting of the American Society for Parasitologists we caught up briefly. He’d been off to Zambia and various other seething leech hot spots since I’d last seen him, and at the meeting he and his students were presenting lots of new research, including some insights into how different species of leeches thin your blood.

Just a couple days later, on Wednesday, Siddall launched his blog with an impressive six posts by the afternoon–including Demi Moore waxing poetic about leeches on her navel.

This is why the Internet was invented.

I’m sure you’d like to pretend that you have nothing in common with a tapeworm.

A tapeworm starts off as an egg which then develops into a cyst. Inside the cyst is a ball-shaped creature with hooks that it can use to crawl around its host before growing into an adult. Many species are made up of dozens or hundreds of segments called proglottids. Each proglottid may be equipped with both eggs and sperm-making organs. As an adult, a tapeworm also grows a head-like end often equipped with suckers or hooks of its own. This strange organ is called the scolex. (The shark tapeworm in this photo is displaying its fearsome scolex.) While the tapeworm lives in the gut of its host, it uses its scolex to clamp down in place, although it may swim around to find an ideal spot from time to time.

And from time to time, a proglottid breaks off from the body of the tapeworm and ends up leaving the body. Actually, it can leave under its own steam. Proglottids have muscles and nerves that they can use to crawl out the back end and along the ground.

Tapeworms evolved from free-living flatworms, but they have undergone some radical changes. Along with the evolution of their proglottids, they also abandoned their digestive tract, opting instead to slurp up their food directly through their skin. They’re so weird now that scientists haven’t even been sure which end is which. Some people have suggested the scolex is the head of the tapeworm. But others have pointed out that while the tapeworm is still in its cyst, the hooks actually form on the other end of its body. What’s more, in related flatworms with recognizable heads and tails, the sperm-organs are closer to the head than the ovaries. In tapeworms, the ovaries are closer to the scolex.

This morning at the second day of the American Society of Parasitologists, Peter Olson from the Natural History Museum in London, offered a potential solution to the puzzle. All animals–including us–use a set of master genes to determine the head-to-tail anatomy of developing embryos. The precise DNA sequence of these genes is different from species to species, but they show clear evidence of having evolved from a set of genes in a distant ancestor. Scientists have carried out most of their research on these genes in well-studied species like fruit flies and mice. Only recently have scientists started to look at how these so-called Hox genes work in other animals. Olson is studying the genes in tapeworms that live in mice, called Hymenolepis.

One key gene Olson described is called Post-2. It corresponds to genes that defines the tail end of insects and mammals. When tapeworms develop into little balls with hooks, Olson has discovered, Post-2 becomes active on the end of the ball with the hooks. That suggests that the hooks are growing at the tail-end of the animal, before it has yet grown a tail.

Later, when the tapeworm develops into an adult with proglottids, Post-2 becomes active at one end of each segment. It becomes active at the end furthest from the scolex. So the tail end of the animal appears to be pointing away from the scolex–in other words, the scolex really is the head after all. It may not be a head you’re familiar with–sans teeth, sans eyes, sans taste, although not quite sans everything. But when the tapeworm grew its head, it knew where it was the same way you knew when you grew yours.

[Edited a bit to address questions from commenters.]

It feels like a homecoming: I’m among hundreds of people who live for parasites.

I arrived in Arlington Texas this afternoon to attend the annual meeting of the American Society of Parasitologists. I’m going to give a talk tomorrow about the public awareness of parasitology, talking about my long-term relationship with the beasties in books, articles, blogs, and beyond. But till then, I get to hang out with parasitologists. I’ve met a lot of the people here over the years, like the leech-master Mark Siddall, and I’ve read the work of a lot of people I’m just meeting (work on things like how lice jumped from gorillas to human ancestors).

And I’m also hearing new people talking about research I’ve never heard before–”nice and weird,” as one parasitologist described the species she studies. I heard about a parasite in Nebraska, a flatworm called a trematode (Halipegus eccentricus), that scientists discovered living in the ears of bullfrogs. But the trematodes in their ears are all adults. Matt Bolek from the University of Nebraska described how he and his colleagues had figured out the rest of the parasite’s life cycle. The parasites release their eggs from the frog ears, which then get scarfed up by snails, where they hatch and start to develop. Then they leave the snails and swim in search of little aquatic invertebrates called ostracods. The ostracods get eaten by the larvae of damselflies, which then mature and fly into the air, only to be devoured by frogs. The parasites escape the damselflies and move through the bodies of the frogs to their ears. One trematode, four hosts.

And you thought your commute was long.

Tomorrow I’ll blog about more of these marvelous beasts.

[Image courtesy of Matthew Gilligan]

[Update: In answer to commenters–that’s an invertebrate known as a isopod that’s eaten the fish’s tongue and is now sitting where the tongue used to be. Nice and weird, baby.]

In a couple weeks I head to Texas to the annual meeting of the American Society of Parasitologists to talk about parasites in pop culture. The symposium is called, “Parasitology: Public awareness through literature, art, and film.” Our panel has lots of creepy movie clips in store, plus other sorts of media including books and this humble blog. But maybe we’ll need to tack on “music” to the end of that list in the symposium title. Inspired by a post of mine on the gorey glam of Ampulex compressa , the emerald cockroach wasp, a band called Super Duper has composed a song. The video is below, and the lyrics below that…

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A caterpillar’s life is not an easy one. The plants that it eats make toxins to make it sick. Birds swoop in to pluck it away and feed it to their chicks. But the most horrific threat comes from wasps that use caterpillars as hosts for their young. These parasitoid wasps are among my favorite creatures (see my post on the emerald cockroach wasp, which attacks cockroaches like a neurosurgeon). So it was with eye-popping delight that I read a new paper in PLOS Biology One about how another species of wasp in Brazil attacks another caterpillar. Glyptapanteles glyptapanteles is more than just cruel to its host. It also gives its host an extreme case of Stockholm syndrome.

The fun begins when a female Glyptapanteles wasp comes across a potential host–a moth known as Thyrinteina leucocerae. The wasp inserts a stinger-like probe into the caterpillar’s gut body cavity and injects dozens of eggs. The eggs hatch and grow into wasp larvae, which feed on the still-living host as it continues munching on leaves. The caterpillars even moult and pass through three or four stages with the parasites lurking inside them. Finally, when the wasps have finished their living feast, about 80 of them drill escape holes and crawl out of the caterpillar. They move a few inches away, where they spin cocoons on a twig or leaf, where they will develop into adults.

Many species of wasps exit their hosts this way, and in many cases the hosts promptly die. After you’ve just spent a couple weeks with dozens of parasites sucking your insides dry and then drilling their way out of your body, you’d probably feel like dying too. But in the case of Thyrinteina, death waits. The caterpillar stops feeding and crawling and simply sits, still alive, next to the wasp cocoons. When other insects come by, they wave their heads violently around, so violently they can knock the other insects off the tree. (You can download a movie of this behavior here.) Once the adult wasps emerge from the cocoons, the caterpillars finally expire.

You may be thinking that the caterpillars were turned into bodyguards for their parasites, protecting them from predators. And if it were ture, it would be a particularly striking addition to a long list of cases in which parasites manipulate their hosts for their own well being. I wrote about this manipulation at length in my book Parasite Rex, and have also written about it here on the Loom (suicidal rats, neurosurgical wasps, etc).

When scientists find a host acting weirdly, it’s a reasonable hypothesis that they’re being manipulated by their host parasite. But it’s just a hypothesis, one that cries out for testing. There are other possible interpretations, after all. W,hat looks like a clever adaptation that boosts the parasite’s reproductive success may in fact just by an incidental byproduct of being sick. And a peculiar behavior that scientists observe in hosts they keep in a lab may not be terribly important out in the wild. Parasites sometimes need to go from one host to another to develop–in many cases, traveling from prey to the predators that eat them. If a parasite makes its host an easier target for predators, its host may get eaten by the wrong species of predator, one in which the parasite will die.

To test the bodyguard hypothesis on Glyptapanteles wasps, scientists ran experiments on the animals outdoors, on real guava trees. They observed how parasitized caterpillars behaved around the cocoons compared to healthy ones, and they observed how much protection the infected caterpillars really provided from predators by removing some of them.

The scientists found that almost all the parasitized caterpillars huddled close to their parasite cocoons, often actually crouching over them. When the scientists put cocoons next to unparasitized caterpillars, they simply went on wandering the leaves and twigs, feeding away. When stinkbugs came along, the parasitized caterpillars almost always lashed out, while the healthy caterpillars ignored them. Sometimes the stinkbugs and wasps fell off the tree, and sometimes they just gave up. This flailing made a big difference to the survival of the wasps, the scientists found. Removing infected caterpillars from the neighborhood of the cocoons double the death rate for the wasps.

So the bodyguard hypothesis looks good. But it naturally raises a question: how do the wasp larvae turn the caterpillars into their bodyguards? The catepillars only start fending off predators a couple hours after the wasps had left their bodies. It’s possible that they left behind some chemicals that altered their hosts’ behavior. But when the scientists dissected caterpillars three or four days after the wasps had left, they would find one or two living wasp larvae still inside. Scientists have found other parasites that have stayed behind in their hosts. Ants, for example, are infected by lancet flukes that drive them up to the tops of blades of grass, where they can be eaten by grazing livestock. It appears that they are driven by a few flukes that form cysts in the brains of the ants and can not pass on into their new host like the rest of the flukes. Perhaps the bodyguard caterpillars are being piloted by one or two wasps that stay behind, defending their siblings from predators while surrendering their own lives. Who knew such vicious parasites could be so heroic?

(Photograph by Prof. José Lino-Neto. Covered by a Creative Commons Attribution License. Any use should include citation of the authors and paper as the original source.)

[Note: Thanks for the fact-checking and copy-editing. I’ve fixed the text accordingly.]