Funny&Amazing Pics&Facts: parasites

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вторник, 12 сентября 2017 г.

You don’t actually want these parasites to go extinct

Climate change won't just impact charismatic critters.

Humans might fantasize about a world without ticks, fleas or giant kidney worms. But parasites connect food webs and serve vital purposes in every ecosystem. And scientists aren't really sure what would happen if we lost them.

Biologist Colin Carlson was cooking pancakes with a parasitologist friend when they started talking about the effects that climate change will have on parasites. She thought it would be impossible to track down enough specimens for a comprehensive scientific study. Carlson took that as a challenge, and teamed up with Anna Phillips, a zoologist at the Smithsonian Museum of Natural History, and 16 other scientists from eight different countries. They created a massive database of over 100,000 kinds of parasites, then whittled down their study to around 50,000 species. By tracking how these blood-suckers, stomach-dwellers and kidney-eaters are moving and disappearing as the climate changes, Carlson and his team predicted how parasite populations will shift as this process continues. They found that a third of all parasites face a risk of extinction.

“We very rarely see predicted extinction rates this high for large groups,” says Carlson.

It’s difficult to predict how climate change will alter ecosystems by 2070. Most climate models agree until the 2030s, then temperatures increase at different speeds and forecasts diverge. But even in the best-case scenario, Carlson says, parasites will face some serious reshuffling.

Critters that currently live in warmer climates will move up north—which means more parasites may move up into the U.S. and Canada. It's not clear how parasites that evolved in one environment will behave in a different place. But the fact that they're likely to have fewer natural predators and less competition for the resources they require doesn't bode well. “I think this is sort of the big unknown,” says Carlson. “A new wave of invading parasites will be entering."

And while some parasites are set to stake out new territory, a wide range of species face threats of outright extinction from two sources: the death of their hosts and the changing base habitat. Most parasites spend at least part of their lives in an open environment, often as larva. They swim around in streams or swamps, which makes them vulnerable to changing climates.

The researchers found that parasites affecting humans were as likely to face extinction as those that target other species. However, there was one group of parasitic worms—Acanthocephla—that faced fewer threats than the other groups. These worms don’t usually infect people; their specialty is fish, amphibians, invertebrates, birds and other mammals. The researchers weren't sure exactly why these wrigglers seemed to fare better than other parasites in the models—they may just be geographically lucky. But co-author Anna Phillips says that this strange exception to the rest of the study brought up an important point for her. "We wanted to address parasite diversity on the whole, not just what affects humans," she says. Scientists estimate that 86 to 99.999 percent of species remain undiscovered, and parasites aren't the most glamorous organisms to put your name on. Extinctions will affect ecosystems that we do not yet understand, which makes it impossible to know how other creatures will be impacted. Even for species we're already familiar with, the domino effects remain unclear.

For example, take a pest that is currently plaguing the Northeast—the deer tick, which spreads Lyme diseases and other nefarious infections. Its suitable habitat is actually set to increase by 213 percent by the 2080s, according to a 2005 study. Scientists don't know what effect that spread will have on the ants, spiders, wasps and birds that eat the ticks (and the things that eat them), or the deer and humans that suffer in their wake.

The threat level of each known species is now in a public database. Carlson would have met a dead end soon after that pancake breakfast without the help of museum collections like the U.S. National Parasite Collection, which has been built over hundreds of years. “The researchers in 1892 couldn’t have fathomed the things that we are doing with ecological modeling today,” says Phillips. “We can’t imagine what we’ll be using the specimens for in the future.”

Scientistific studies usually end with a plea for more research. But in this case, the unknowns so outweigh the certainties that trying to predict how the natural world will respond to this loss left the scientists grasping for words. “The impact of losing these parasite species to extinction—we don’t know what that will be,” says Phillips. “It’s really difficult to predict with even of the most optimistic of scenarios what our landscape of biodiversity will look like in 2070.”

суббота, 16 апреля 2016 г.

Having worms can be good for the gut

THE WORM TURNS Intestinal parasites may have an upside. Researchers have discovered that people with whipworms (Trichuris trichiura, left) and mice with Heligmosomoides polygyrus (right) have fewer inflammation-provoking bacteria than they do without the worms.

Parasites trigger immune reaction that can calm inflammation

Parasitic worms may hold the secret to soothing inflamed bowels.

In studies of mice and people, parasitic worms shifted the balance of bacteria in the intestines and calmed inflammation, researchers report online April 14 in Science. Learning how worms manipulate microbes and the immune system may help scientists devise ways to do the same without infecting people with parasites.

Previous research has indicated that worm infections can influence people’s fertility (SN Online: 11/19/15), as well as their susceptibility to other parasite infections (SN: 10/5/13, p. 17) and to allergies (SN: 1/29/11, p. 26). Inflammatory bowel diseases also are less common in parts of the world where many people are infected with parasitic worms.

P’ng Loke, a parasite immunologist at New York University School of Medicine, and colleagues explored how worms might protect against Crohn’s disease. The team studied mice with mutations in the Nod2gene. Mutations in the human version of the gene are associated with Crohn’s in some people.

The mutant mice develop damage in their small intestines similar to that seen in some Crohn’s patients. Cells in the mice’s intestines don’t make much mucus, and more Bacteroides vulgatus bacteria grow in their intestines than in the guts of normal mice. Loke and colleagues previously discovered that having too much of that type of bacteria leads to inflammation that can damage the intestines.

In the new study, the researchers infected the mice with either a whipworm (Trichuris muris)or a corkscrew-shaped worm (Heligmosomoides polygyrus). Worm-infected mice made more mucus than uninfected mutant mice did. The parasitized mice also had less B. vulgatus and more bacteria from the Clostridiales family. Clostridiales bacteria may help protect against inflammation.

“Although we already knew that worms could alter the intestinal flora, they show that these types of changes can be very beneficial,” says Joel Weinstock, an immune parasitologist at Tufts University Medical Center in Boston.

Both the increased mucus and the shift in bacteria populations are due to what’s called the type 2 immune response, the researchers found. Worm infections trigger immune cells called T helper cells to release chemicals called interleukin-4 and interleukin-13. Those chemicals stimulate mucus production. The mucus then feeds the Clostridiales bacteria, allowing them to outcompete the Bacteroidales bacteria. It’s still unclear how the mucus encourages growth of one type of bacteria over another, Loke says.

Blocking interleukin-13 prevented the mucus production boost and the shift in bacteria mix, indicating that the worms work through the immune system. But giving interleukin-4 and interleukin-13 to uninfected mice could alter the mucus and bacterial balance without worms’ help, the researchers discovered.

Loke and colleagues also wanted to know if worms affect people’s gut microbes. So the researchers took fecal samples from people in Malaysia who were infected with parasitic worms.

After taking a deworming drug, the people had less Clostridiales and more Bacteriodales bacteria than before. That shift in bacteria was associated with a drop in the number ofTrichuris trichiura whipworm eggs in the people’s feces, indicating that getting rid of worms may have negative consequences for some people.

Having data from humans is important because sometimes results in mice don’t hold up in people, says Aaron Blackwell, a human biologist at the University of California, Santa Barbara. “It’s nice to show that it’s consistent in humans.”

Worms probably do other things to limit inflammation as well, Weinstock says. If scientists can figure out what those things are, “studying these worms and how they do it may very well lead to the development of new drugs.”

Gut reaction

In normal mice (top), the cells lining the intestines form fingers reaching toward the hollow center. In mice with a mutation in the Nod2 gene (middle), the intestinal lining is often swollen and damaged (an abscess shown). But infecting mutant mice with a whipworm (Trichuris muris) can restore the gut to health (bottom) by promoting mucus production and shifting the mix of bacteria that live the intestines.

Citations

D. Ramanan et al. Helminth infection promotes colonization resistance via type 2 immunity.Science. Published online April 14, 2016. doi: 10.1126/science.aaf3229.

D. RAMANAN ET AL/SCIENCE 2016

суббота, 25 июля 2015 г.

Absurd Creature of the Week: The Barnacle That Invades Crabs in a Not OK Way

A rhizocephalan infecting a hermit crab.

The most miserable rainbow on Earth. That's a hermit crab with a rhizocephalan parasite, which comes in a lovely shade of yellow. ARTHUR ANKER

CRABS GET A bad rap. After all, people who are into cheerfulness call me “crabby” all the time. But let’s cut them some slack (the crabs, not the cheerful people—forget them), because a lot of these critters could be going through some stuff. And by stuff I mean what has to be one of the most disturbing and wildly complex parasitizations in the animal kingdom.

So the rhizocephalans are these species of barnacle, and unlike most barnacles, they aren’t content living life stuck to rocks. Indeed, they look nothing like barnacles. Well, they start out as regular barnacle-ish larvae, shaped like an oval, but that’s where the similarities end. Instead of developing into your classical shelled variety, they invade the bodies of various crab species. And not as mere tiny hitchhikers: After penetrating a crab’s shell, a rhizocephalan grows as meandering roots throughout its victim’s flesh, sometimes reaching nearly every part of its body.

And then things start getting weird.

That mass on the lower bit of the crab's abdomen is a parasitic barnacle. The other bits are its legs and claws, but you probably already knew that. — That mass on the lower bit of the crab’s abdomen is a parasitic barnacle. The other bits are its legs and claws, but you probably already knew that. HENRIK GLENNER

Like a Tree, Only It Grows Inside You and Instead of Drinking Water It Drinks Your Bodily Fluids

Life for a rhizo begins as an aforementioned larva, which is tasked with the seemingly impossible mission of not only finding the right species of crab (they tend to be able to infect just one type—that is, they’re highly “host-specific”), but somehow landing on it in the vastness of the sea. Rhizo babies appear in huge numbers, though, so by pure chance a few are bound to find their target. The rest—well, points for trying.

When one lands on a crab, it makes its way to one of the host’s many sensory hairs, known as setae, where the carapace is the weakest. Here the rhizo secretes a cement to anchor itself, just as a typical barnacle would. Next “it forms a so-called stylet, which is a hollow structure,” says Henrik Glenner of Norway’s University of Bergen. “It’s almost arrow-shaped, and with this it penetrates the cuticle of the host.”

A rhizo larva in its days of relative innocence. Ah, to be young again and not torturing crabs. HENRIK GLENNER

With this syringe, the rhizo injects cells of itself into the crab’s hemolymph, the invertebrate equivalent of blood. And you know how bad a sinus infection feels? Well, the rhizo ends up in the hemolymph sinuses, much to the chagrin of the crab. It’s here where it starts to grow as roots, which have a covering that somehow protects them from a potential immune response as they work their way through the host. They’ll soak up massive amounts of nutrients from the crab, and the roots can end up pretty much anywhere, even in the claws.

All the while, the crab is still miraculously growing, periodically shedding its exoskeleton. But eventually it stops, likely because the rhizo is appropriating too much of its nutrients. It’s at this point that the parasite enters its next stage: sexy time.

The Merits of Being Pretty Much Just a Testicle

Because the crab is no longer molting its exoskeleton away, the rhizo can now extend itself out of the host, forming a mass on the crab’s abdomen. “The funny thing about this is that this sac-like structure, the externa, is situated exactly where an adult female crab would have its egg mass,” says Glenner. “And we don’t know what the mechanism is, but the host considers the parasite as a part of itself.” The crab even takes care to groom and ventilate the sac, full of the rhizo’s eggs. (If the rhizo has infected a male crab, the host will actually start transforming morphologically, widening its abdomen to more closely resemble a female. This serves as better protection for the sac: If it grows on a wider abdomen, it won’t overflow past the edge of the carapace.)

All the more incredible, the rhizo is pulling this all off without a brain of its own and only the remnants of a nervous system. And the commandeering doesn’t end at the crab caring for the parasite. Somehow, the rhizo directs the crab away from the general crustacean population into deeper waters, thus avoiding feeding competition with healthy crabs. Non-parasitized gravid (that is, preggers) females do this with them, since they’ll find better protection from their enemies in the depths.

Another parasitized crab. It too has "legs." — Another parasitized crab. It too has “legs.” HENRIK GLENNER

Now, it’s only female rhizos that infect crabs. Dwarf males look much like the larval form, and must somehow find not only a specific species of crab, but a specific species of crab that’s been invaded by a female. And that female has to be a virgin. The search, as you might expect, can be rather frustrating.

But should a male find a virgin female, he inserts himself into receptacles in her sac-like structure. “There the male changes form completely and becomes just a mass of cells,” says Glenner. “And actually it becomes a functional testicle, nothing more, and it’s nursed by the female. Then they are united for life.” Again and again, the male produces sperm to fertilize her eggs.

The eggs will hatch right inside the female, and when she’s ready to release the larvae, she gets an assist from her host. Your regular unparasitized female crabs will raise themselves up and shake their abdomens to disperse their eggs, and so too do infected crabs shimmy as the rhizo pumps out its larvae, boosting them into the water column. And off they go to infect still more crabs.

As a final insult, during all of this the crab itself cannot reproduce, for the rhizo has sterilized it. A lot of parasites do this—energy that the host isn’t putting toward reproduction can instead go to the parasite. The rhizo may pull this off with some kind of chemical, or it may just be a matter of exhaustion for the crab. Remember that all this time the parasite has been sapping it of nutrients, so it could be that the crab has gone into dire survival mode, and reproduction is the first thing that goes.

“The crab is not a crab anymore,” says Glenner. “It’s a device for the parasite because it cannot reproduce itself. But it behaves as if it were reproducing all the time.”

Yet it will not die. In fact, the parasite has a shorter lifespan than the crab and may therefore perish first, leaving the victim with the tell-tale scars of rhizo on its abdomen. That, and probably some serious existential angst.

AUTHOR: MATT SIMON.

понедельник, 22 декабря 2014 г.

This Is What Parasites Look Like Under An Electron Microscope

by julia.letts

When reddit user reddit_scientist took his dog out for a walk, he didn't think anything out of the ordinary would happen. Less than an hour later, he knew something was wrong. As he was out driving, his foot started to itch. He thought he could ignore it, but it got worse and worse. When he pulled over, he noticed something was off.

It looked like there was dirt on his foot, only the dirt was crawling. As he described it, they were small, brown, crawling insects that looked just like ticks. Luckily, he was pulled over at a gas station so he could run into the bathroom to try to scrub them off.

Of course, as his username implies, he's a scientist, so he had to save a couple for examination. He was fairly sure they were harvest mites, which he describes as a type of parasite (only when in larva stage). Since he had access to a scanning electron microscope at work, there was no option but to investigate further. This is what he found: