Blogs / The Loom

Marcel Salathe, a biologist I know at Stanford, is running a very cool study on swine flu psychology that you can be a part of. Here’s the dope from Marcel:

 As you have heard in the news, there has been an outbreak of swine flu in Mexico and the United States. There is a possibility that this situation might develop into a pandemic if the virus continues to spread around the globe. The news media report excessively about this threat, and while health officials urge people to stay calm, there is an increased level of anxiety in the population.

Models have predicted that when a disease breaks out, changes in behavior in response to an outbreak, and in particular in response to information about an outbreak, can alter the progression of an epidemic. While this makes intuitive sense, there is no good data to test such a hypothesis. One of the major problems is that emotional reactions and behavioral response to an epidemic is generally assessed quite some time after the epidemic has fizzled out.

We would like to address this problem by starting a survey about risk assessment and personal responses to a potential epidemic as it unfolds – that is, right now.

Please help us achieve this goal by filling out a simple questionnaire (link below) – it shouldn’t take more than five minutes.

This is the link:
https://opinio.stanford.edu:443/opinio/s?s=1403

I’ve just taken the survey, and I can vouch it’s quick and painless. When Marcel has results to share, I’ll make sure we get his analysis. So please help him out–take the test and spread the word.

Excellent lecture on parasites from Jim McKerrow, courtesy of FORA.TV. McKerrow helped me out long ago with information and pictures of blood flukes when I was writing Parasite Rex. But he can deliver great tales about all sorts of critters inside you.

Animals, as I explained in my recent column for Discover, take precautions not to get sick (including the famous anal cannon). We take precautions too–conscious ones, based on what we have learned about how diseases spread, and perhaps also unconscious ones that lower our risk of infection.

But if those precautions fail, we humans sometimes take medicines to kill off the pathogens making us sick. And there’s an intriguing body of evidence suggesting that animals take medicine too.

A lot of that evidence comes from studies on chimpanzees, our closest living relatives. When they get infected, they will sometimes devour leaves and other vegetation they otherwise never touch. In the case of one plant, the chimps have to first peel away an outer covering that is lethally toxic. They  go to these lengths, it appears, because eating these plants can cure them of their ills. Some plants can flush parasites out of the gut and others actually fight the pathogens themselves. In fact, when researchers study the plants chimpanzees eat, they discover new compounds that kill bacteria and other pathogens. They look promising as medicines for people. (pdf).

Given the sophisticated minds of chimpanzees (they can, for example, plot rock-hurling attacks on zoo-goers), it’s possible that chimpanzees teach themselves which medicinal plants to take, and these medical traditions spread culturally. But other animals seem to eat peculiar things when they get sick, too. Even insects do. Obviously, no invertebrate has ever graduated from medical school. (Insert your doctor joke here.) So the question arises, are insects actually self-medicating, or are they getting so sick that their diet goes haywire?

In a new paper published in PLOS One, Michael Singer of Wesleyan University and his colleagues carefully tested these alternatives in an experiment on woolly bears (Grammia incorrupta). A lot of woolly bears get killed by parasitic flies and wasps. The flies and wasps lay their eggs inside the woolly bears, and the larvae hatching from the eggs devour their hosts from within.

But a lot of these parasites die inside the woolly bears, and the hosts recover in good health. The immune system of the woolly bears probably kills off some of the eggs. But Singer has observed that some of the plants woolly bears feed on contain pyrrolizidine alkaloids, which are some truly nasty chemicals. So Singer and his colleagues looked into whether the woolly bears eat the alkaloids to medicate themselves against parasites.

The researchers fed infected and uninfected woolly bears food that included alkaloids or was alkaloid-free. They found that the infected woolly bears that ate alkaloids were 17% more likely to survive long enough to develop into moths. Their success was due to the parasite-killing power of the alkaloids–many fewer parasitic flies emerged from alkaloid-eating woolly bears than from hosts fed an ordinary diet.

But alkaloids are not to be taken lightly–like many medicines, they can have some nasty side effects on their hosts. Uninfected woolly bears that ate alkaloids were 18% less likely to survive to become moths than woolly bears that didn’t eat them.

Singer’s team also found that infected woolly bears eat more alkaloid-laced food than healthy ones. Another test of the medication hypothesis was not so clear, though. The scientists allowed the woolly bears to choose between food with alkaloids and food without them. Putting more fly eggs in a host did not lead it to choose to eat more alkaloids. But among the infected woolly bears that survived to become moths, the ones that were infected with two eggs turned out to have eaten more alkaloids. It’s possible that the ambiguity in the choice experiment was due to the woolly bears killing off the parasite eggs with their own immune systems, making it unnecessary for them to medicate themselves.

Singer and his colleagues propose that woolly bears can medicate themselves with the alkaloids. What’s more, they do so without learning like chimpanzees do. A woolly bear’s immune system recognizes invading parasites, and alters the animal’s nervous system so that it gets a stronger preference for the taste of alkaloids.

Their hypothesis is, to the say the least, intriguing. How many other insects are healing themselves with medicinal plants? Did the common ancestor of insects and humans have this ability too? Did our ancestors once have these hippocratic instincts, which have since been lost? Or do some foods (or even dirt) taste just a little better when our bodies detect an unwelcome visitor?

Update: Dr. Singer kindly jumped into the comment thread to respond to some questions about his research. Among other things, he notes that woolly bears move around from plant to plant as they feed, so their choice of chow is not limited by the cost of travel.

There are two things I really like to learn about: parasites and the human mind. And so I was intrigued to learn about some studies that suggest that we defend ourselves from infections not only with an immune system made up of cells and antibodies, but one made up of unconscious behaviors. It’s the topic of my new column about the brain in Discover. Other people can make us sick, and so perhaps we deal with them differently depending on our risk of getting sick. Take this study, from Carlos Navarrete, a psychologist at Michigan State University. He and his colleagues designed an experiment to compare how pregnant women respond to strangers. During the first trimester, both mother and child are particularly vulnerable to infection.

Navarrete and his colleagues had 206 pregnant women read two essays that were written, they were told, by students. One of the essays was by a foreigner who criticized the United States, the other by an American who praised the country. The women then had to rate the essayists for their likability, intelligence, and other qualities. Women in the first trimester were more likely than those in the second or third trimester to give a high score to the American and a low score to the foreigner. The pregnant women’s vulnerability to infection, Navar­rete concludes, brought with it a heightened disapproval of foreigners.

You can read the whole thing here.

Drat. Robert Sapolsky is going to give a public lecture next month about his cool work on parasites and mind-control. (For details, see this article I wrote for the New York Times.) But there’s no way I’ll be anywhere near the venue. Details are below–and below that, a video of a talk Sapolsky gave in November that I’m going to have to settle for…apologies for the absurdly obtuse angle of the camera.

NATIONAL INSTITUTE OF MENTAL HEALTH DIRECTOR’S INNOVATION SPEAKER SERIES

Title: Do Parasites Know More Neurobiology Than We do?
Speaker:  Robert Sapolsky PhD
February 26, 2009, 3-4 PM
Neuroscience Center, Conference Rooms C & D
6001 Executive Boulevard  Bethesda, MD

For the third year, the National Institute of Mental Health is pleased to invite you to attend the fifth of a series of lectures dedicated to innovation, invention, and scientific discovery. Dr. Robert Sapolsky is currently the John A. and Cynthia Fry Gunn Professor at Stanford University, holding joint appointments in several departments, including Biological Sciences, Neurology & Neurological Sciences, and Neurosurgery.

This lecture will cover a remarkable phenomenon — the parasite Toxoplasma gondii can only reproduce sexually in the gut of cats.   Once excreted from it, it then often infects rodents.  In order to complete its life cycle and return to the stomach of cats,  Toxoplasma has evolved the remarkable ability to convert the innate fear that rodents have of cat odors into an attraction to them.   In this talk, Dr. Sapolsky will review the small literature beginning to explain how this microscopic parasite can manipulate the neurobiology of fear and anxiety.

This event is open without prior registration to all NIH staff and the general public. Parking is available at a nominal fee. A government-issued photo-identification card (e.g., NIH ID or driver’s license) is required to gain entrance to the building. This event will not be web/video cast or video taped.

It’s been nine years since I published Parasite Rex, but it just got a very cool honor. Amazon has named it one of their highest-rated science books. The criteria are a little squirrely, but I won’t turn it down.

May all your parasites in 2009 be as lovely as this one, sent from Bonaire by my friend David Fishman.

Madagascar has long been famous for its peculiar biodiversity, from its lemurs to its baobob trees. In the mid-1700s, the French naturalist Philibert
Commerson wrote,

May I announce to you that Madagascar is the naturalist’s promised land? Nature seems to have retreated there into a private sanctuary, where she could work on different models from any she has used elsewhere. There you meet bizarre and marvelous forms at every step…

None of the island’s land mammal species are found anywhere else on Earth; 95% of the reptile species and 99% of the amphibians are unique as well. Over 15% of all the primate species on Earth live on Madagascar, which makes up only .4% of the Earth’s land surface.

It separated from Africa about 120 million years ago, and is now separated by a channel some 250 miles across. Madagascar remained attached to the Indian subcontinent for millions of years more, but eventually they pulled apart as well, with India heading north towards Asia and Madagascar staying put in deep isolation. The species that were on board Madagascar at the separation continued to evolve there. New species arrived later, but only rarely. It’s possible that they drifted from Africa on giant rafts of vegetation swept to sea by storms, or lived on islands that existed for a time between Madagascar and the continent. In any case, Madagascar became both a laboratory and a museum. Many new species evolved, adapting to open ecological niches. And while old lineages became extinct elsewhere, they survived on Madagascar. The only primates on Madagascar are the lemurs. They represent the oldest lineage of primates alive today on Earth, having branched off from other primates about 70 million years ago.

I guess it was just a matter of time before someone discovered that Madagascar is a museum for viruses as well.

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You go for a swim, and you don’t even notice the tiny worm that burrows into your skin. It slips into a vein and surges along through the blood for a while. Eventually it leaves your blood vessels and starts creeping up your spinal cord. Creep creep creep, it goes, until it reaches your head. It curls up on the surface of your brain, forming a hard cyst. But it is not alone–every time you’ve gone for swim, worms have slithered into you, and now there are thousands of cysts peppering your brain.

And they are all making drugs that are seeping into your neurons. These drugs are a bit like Prozac, except far more sophisticated. They target certain neurons in certain parts of the brain, altering your behavior surgically, without unwanted side effects.

You don’t know what’s happening to you. But in situations in which you’d expect to feel scared or stressed, you just want to race around. You whirl in circles, doing whatever is necessary to get the attention of the very thing that terrifies you. Thanks to your uncontrollable flailing, that terror  finds you, and you are destroyed.

This is how I imagine you’d feel if you were a fish infected by a parasitic worm called Euhaplorchis californiensis.

I first encountered these remarkable parasites about ten years ago, when I took a trip out to Santa Barbara. In the estuaries and salt marshes along the California coast, one of the most common fish is the California killifish, and many of them carry the parasites. The parasites get their start in horn snails, where they produce offspring that can swim around the water searching for killifish. In their next phase, they live as cysts on the brains of the killifish, but in order to reach the stage when they can reproduce, they must get inside the guts of shore birds.

Kevin Lafferty, who studies these parasites, showed me a tank full of infected killifish. Despite having thousands of cysts on their brains, they could swim as vigorously as uninfected killfish. They can also get as much food as healthy fish and reproduce normally. But the fish in the tank acted oddly. They swam up near the surface of the water, making tight turns that showed off their glinting sides. It’s tempting to say that the fish are trying to make themselves as conspicuous as possible, but for a fish, it doesn’t really matter how conspicuous it is to a human. So Lafferty had run an experiment to see whether the birds thought the infected fish were acting oddly. There is indeed a difference–the infected fish are 10 to 30 times more likely to get grabbed by a fish bird than a parasite-free one.

Many parasites have evolved such wickedly elegant strategies for manipulating the behavior of their hosts for their own benefit (which I describe at more length in my book Parasite Rex). But exactly how they do this parasitological voodoo is quite mysterious. A number of studies suggest that parasites release chemicals that can precisely alter the way in which the nervous systems of their hosts work. But it’s easy for parasites to hide a potent drug in the normal flow of neurochemistry in the brain. It’s also possible, at least in some cases, that parasites don’t do much of anything to manipulate their hosts. Just being infected can affect how animals behave–in some cases making them sluggish, in some cases stressing them out.

Jenny Shaw, a post-doctoral researcher at the University of California at Santa Barbara, has been working with Lafferty and other colleagues to figure out how Euhaplorchis manipulates the killifsh. They’re reporting some early results in a new paper in the Proceedings of the Royal Society. While they haven’t found the Parasite Panic Pill just yet, they do have some intriguing results. They took tiny pieces from different regions of the brains of infected and clean killifish. In each chunk of brain, they measured levels of neurotransmitters such as dopamine and serotonin. To compare the effects of parasites to ordinary stress, they also looked at the brains of stressed killifish (you stress a killifish by lowering the water in its tank).

Shaw and her colleagues found that the brain of an infected fish is not the brain of a stressed fish. When healthy fish get stressed, they produce serotonin in a region of the brain called the raphe nuclei. The parasites block that response. The parasites also lowered serotonin in the hippocampus, while boosting dopamine in the hypothalamus. The more parasites a fish had, the stronger these effects were.

Shaw and her colleagues point out that in normal fish, a surge of serotonin can cause fish to freeze, which is a good way to hide from motion-sensing predators. By lowering the serotonin from the raphe nuclei, parasites may prevent fish from hiding from wading birds. Dopamine, on the other hand, stimulates fish to swim more and behave aggressively. It’s possible that a parasite-boosted level of dopamine also helps turn fish into bird breakfast.

It may be years before someone finds the molecules these parasites release to cause these changes in serotonin and dopamine. But in the meantime, it’s pretty mind-blowing to think that there are literally millions of fish in the waters off of California being drugged by their parasite overlord. Scientists may have to wait a while before they can speak definitively about the medicine chests of the puppet masters, but science fiction novelists (I’m talking to you, Scott Sigler) are welcome to start their engines.

Shaw et al, Parasite manipulation of brain monoamines in California killifish (Fundulus parvipinnis) by the trematode Euhaplorchis californiensis, Proceedings of the Royal Society doi:10.1098/rspb.2008.1597

[Image from Jenny Shaw's web site]

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.