It was another Saturday in the lab, the time past 2 a.m. Zi Wang was again spending it alone, with the parasite.
Located behind access-restricted doors on the ninth floor of a research building on the campus of the Washington University School of Medicine, the lab is active at all hours, bustling with staff scientists, post-doc researchers and graduate students. They work under the watch of Dr. David Sibley, each investigating some aspect of the parasite Toxoplasma gondii, commonly shortened to Toxo.
Toxo is a single-celled parasite that infects billions of people. It causes a disease called toxoplasmosis, and while many people who are infected never even realize it, for some with weakened immune systems, it's a monster capable of killing its host. It can damage the eyes or other organs. For infants who are affected in the womb, it can lead to brain damage.
No vaccine currently exists for Toxo. Scientists have spent the last century piecing together how Toxo spreads, infects and attacks the immune system. One day, scientists hope, these discoveries will become building blocks for effective treatment.
In 2016, Wang was a 28-year-old Ph.D. candidate. He had joined the Sibley Lab because he was drawn to a different question involving the parasite, one that's even less understood than its effects on the body. He wanted to explore its effects on the mind — specifically the minds of rodents.
Researchers running behavioral tests in the mid-1990s first began noticing that rats and mice infected with Toxo lost some of their natural fear of cats. In fact, the rodents seemed attracted, sexually, to the scent of their predator's urine.
Originally a fringe line of inquiry, it gained credence as a half-dozen labs corroborated the strange effect. Scientists began to ponder what it meant. Clearly, the theory went, the parasite was messing with its victims' brains.
There was an elegant logic at play, and it posed an irresistible puzzle for the young scientist: Toxo, for all its widespread success, can only reproduce in cat intestines. (That's one reason pregnant women are warned against handling cat feces.) Turning a mouse into a zombie that's horny for its natural predator has all the marks of a good deal for the parasite, shuttling it to its preferred feline host.
Another angle spurred Wang's interest: a different, more human-centric question.
"These parasites are obviously altering the behavior of mice when they get into the brain," Wang says. "And three billion people have this in their head."
Now employed as a scientist at Sigma-Aldrich, Wang's current work focuses on testing and performing product demonstrations for gene-editing equipment. Still, he's no less fascinated by the question behind Toxo's mind-control powers. For him, it's the one that got away.
Several studies had detected statistical connections between Toxo infection and mental illness, particularly schizophrenia. But without a mechanism, and without explaining how Toxo might cause mental problems, these studies are essentially correlation, an interesting connection and little more.
The question for Wang, in his own words: "Is this causing subtle behavioral change for huge chunks of people?"
During his time in the Sibley Lab, Wang's research was unique among his colleagues. He wasn't studying one small battlefield after another in the parasite's war on the immune system. Instead, he sought to conclusively evaluate researchers' best theory of Toxo's brain manipulation.
It was, Wang says, "a beautiful theory."
The delicate genetic engineering consumed more than five years of his life, and his conclusion couldn't have been more different from his expectations. Not only did Wang rip enormous holes in the hypothesis, but his results called into question longstanding assumptions about the parasite's activity in the brain. He had set out expecting to make a breakthrough, and instead added doubt. He made a mess of the beautiful theory.
Yet, Wang still looks back at that Saturday in 2016 with wistfulness, particularly that moment, early in the morning, when he bolted up from his samples and let out a whoop, bounding into the hallway on a dual rush of relief and triumph.
"I was skipping down the halls of the lab at two in the morning, just screaming, jumping for joy," he recalls. "I was convinced that what I had was what I was looking for."
David Sibley had already spent twenty years studying Toxo when Wang joined his lab in 2012. Sibley remembers giving the grad student a warning.
"When I agreed to let Zi do this project, I told him, 'Whether you prove it's probably right or whether you disprove it, you have to be willing to accept either outcome, and think that they're equally interesting.'"
It's early afternoon inside the Sibley Lab, and its namesake, a professor of molecular microbiology, sits behind his office desk. His bike leans on a wall just outside, and the door is covered with blown-up photos of Toxo, a subject that's captivated his entire scientific career. In the dyed colors of the photographs, the parasite's rosette form looks like a strangely delicate flower, one stained in garish greens, yellows and blues.
The lab opened in 1991, and on any given day, Sibley supervises more than a dozen projects while guiding the lab's ongoing work to deconstruct the mechanisms that make Toxo what it is. Around 2000, Sibley read the first studies that described curious behavioral changes in infected rodents, but until Wang, no one in the Sibley Lab followed up on that research.
In the brain, neurotransmitters work as chemical messages delivered to different parts of the body, triggering impulses that range from movement to emotion. The dominant theory for Toxo's behavioral modification was staked on a 1985 lab study, conducted a decade before scientists starting suspecting Toxo of precision brain-manipulation. It found that infected rodents' brains were being hit with a fourteen percent bump in the neurotransmitter dopamine.
Some neurotransmitters perform multiple functions, taking multiple pathways in the brain. Dopamine is one of the most versatile, affecting, among other things, motor control — people with Parkinson's suffer from low levels of dopamine — but also influencing such things as attraction, anticipation, reward and sexual gratification.
"If you alter levels of dopamine, you can change things fundamentally," Sibley says. "The idea was, the parasite lives in the brain, and they're making a precursor and sort of feeding this into the neurotransmitter system. That's what's causing the behavioral change."
Critically, the dopamine hypothesis seemed to account for the statistical connection between Toxo and schizophrenia, whose sufferers frequently have elevated levels of dopamine. Dopamine was also believed to be a likely cause of Toxo's mind-control powers in rats, as it is critical to the brain's processing of fear and risk responses.
If Wang could prove that Toxo relied on dopamine to make rats attracted to cats, that wouldn't just be news for the animal kingdom. Our species shares much of its biology with rodents, and scientists would be confronted with a strong suggestion that, for humans as well as mice, Toxo was not a benign guest.
But Sibley was skeptical of the dopamine theory. It was too simple. Toxoplasmosis threw the body's immune system into chaos, inflaming tissue and implanting thick-walled cysts in seemingly no order across the brain and skeletal muscle. Other unknown side effects could be at work simultaneously. And elevated dopamine levels in rat brains didn't explain why this multi-talented neurotransmitter was generating such specific cat-related behavior.
Wang, on the other hand, says he expected to confirm Toxo's secret assault on the brain. He believed he would prove the dopamine theory correct.
"I came into this with high hopes of solving this whole problem, and answering a huge puzzle about mental illness," Wang says. "I remember my first thesis committee meeting, the professors asking, 'What if you're wrong, what if you don't see these changes?' And I thought to myself, 'What a dumb question.'"
Despite Sibley's earlier admonition — that a researcher should accept either outcome — Wang readily admits that he undertook his research "desperately wanting this to be true." Decades of previous research backed up that optimism, and the theory made intuitive sense. Sure, Sibley's objectivity is noble, but nobility isn't always glorious. Wang wanted to be right. He wanted to build upon the work of the other scientists, to add his link to the chain of hypothesis and experiment.
Sibley's lab isn't equipped for behavioral tests — there are no mice in cages here — but its specialty in genetic engineering gave Wang exactly what he needed to evaluate the theory. He sought to build on the work of the 1985 study, as well as later experiments that appeared to confirm it.
In 2009, a British lab published a groundbreaking paper on Toxo, directly implicating two of the parasite's genes, AHH1 and AHH2, for the dopamine spike detailed in the 1985 study. Wang planned to target those genes.
Using genetic engineering, Wang would snip out the two dopamine-producing genes from Toxo, and then use that mutated parasite to infect mice. If the infected rodent brains showed dopamine levels similar to those in non-infected mice, it would suggest that Toxo had lost its dopamine-producing power.
Ultimately, if the theory was right, a mutated parasite that can't tweak dopamine should lose its mind-control powers, and the infected rodents would behave normally around cat urine.
On the other hand, if the infected animals' dopamine levels stayed high, the deleted genes couldn't be tied to the increased dopamine in the brain. Something else would have to be causing the elevated levels.
Wang's first step was to trick the parasite into erasing its own genes. He started by growing the parasite strain, nourishing them on a diet of foreskin stem cells. Then he electrocuted them repeatedly, until the current opened gaps in the cell wall large enough to introduce artificial "knock-out" genes designed to fool the cell's automatic repair function. Blind to the swap, the parasite replaced H1 and H2 for the lab-created filler DNA.
As precise as the lab tools were, the genes seemed to resist Wang's editing. After knocking out H2 in 2012, it took him four years to reach the moment where he skipped down the lab hallway believing he'd finally knocked out H1. He soon learned that his 2 a.m. victory dance was actually celebrating a false positive that set him back months.
Months later, he skipped down the hallway on yet another false positive. It wasn't until late 2016 that Wang finally managed to create a mutated version of Toxo missing its H1 DNA. Wang could finally celebrate in earnest.
But even at the height of his scientific optimism, Wang was bracing against a mounting pile of evidence that something was wrong with this model. In fact, the dopamine hypothesis was starting to fall apart.
On the first Saturday in May, Zi Wang glides between attendees at the seventh annual Cabaret Risque, a benefit gala for the Gateway Men's Chorus at Soulard's Mad Art Gallery. The crowd is variously dressed in gowns, tuxedos and leather chaps. Around him, suits mingle with burlesque performers, and somewhere in the crowd a professional balloon artist is twisting pornographically detailed versions of a balloon-based Papa Smurf.
It's a bit of a scene, the sort of party where you wouldn't be entirely surprised to encounter a roving magician called "Zi the Mentalist."
Wang guides his willing rubes to a rear room of the gallery. In a previous life, the building was a police station, and it still boasts off-green wall tile and barred jail cells. Four men carrying small plates of appetizers arrange themselves around one of the room's lamp-lit tables. Wang produces a deck of cards.
He's wearing his usual performance outfit — a deep-red dress shirt and a jet-black suit. Wang introduces himself to the table without much flourish. He starts shuffling immediately.
When he turns it on, Wang has the voice of a showman, a blend of assertive storyteller and intentionally hacky standup comic. Beneath the conversation, his hands move like bandits.
The cards chosen by the audience disappear into the deck, only to appear later in some impossible fashion. Cards turn up in Wang's wallet, his sock, his jacket pocket. A three of diamonds, when rubbed just the right way, becomes a queen of hearts in the upturned palm of one astonished patron.
At one point, Wang makes a stack of three cards vanish, and he casually retrieves them beneath a card box on the other side of the table. One of the men, a blonde with a high laugh, leans closer, pressing his forearms against the table in absolute concentration.
For his next trick, Wang bends a chosen card lengthwise, creasing it, and drops it on the top of one half of a cut deck.
"You can see, the bend is right here," Wang remarks, showing the table. Four pairs of eyes stare at the card as Wang buries it beneath the other half of the deck.
Now, the mentalist hovers his hand over cards, and the blonde emits a shriek, then laughs and jerks away from the table. There's the bent card on the top of the deck. Another man wipes a hand over his eyes, as if trying to adjust the grin on his face.
Wang offers reassurance; he never claims to be some supernatural mystic. "It's all just sleight of hand and misdirection," he tells them. "The crazy part is, would you miss it if it happens again?"
They do miss it again. And again. And again.
Wang got into studying magic in college, though he says he's always been a fidgeter, shuffling poker chips and playing cards as a nervous habit long before he learned how to bend the laws of object-permanence.
"There are physical limitations of what you can do with a few pieces of cardboard," Wang says during a brief break in the gala's action. Over the course of two hours, he's made a handful more people sputter in disbelief, their mouths hanging open or caught in mid-groan. They stare at a card in their hand, confounded, their expressions pictures of accusation.
"That's why I love close-up magic," Wang says later. He never tires of these reactions — that mix of surprise and outrage and wonder. "It's the illusion of choice," he suggests, that gets people so riled up. Up close, in physical contact with the cards or within inches of Wang, "they feel like they should have complete control over the outcome of the trick."
Of course, they don't.
"The more fair they feel that it is, the more frustration and joy and wonder comes out of impossible results," he adds. "As a magician, it makes me aware of how flawed my own perceptions are, and the ways in which we're systematically mistaken about the world."
Born in Beijing in the late 1980s, Wang's early life aspirations were shaped by his parents — and those expectations didn't include either geneticist or magician. They wanted him to be a medical doctor. His father's career as a chemical engineer kept the young family moving, and Wang spent time living in Singapore and Toronto before they finally settled in upstate New York.
After high school, Wang moved to St. Louis to attend Washington University, completing an undergraduate degree in biology. By the time he started his Ph.D. program in 2010 he was understandably tired of cross-country relocation. He liked St. Louis and the university's research program, one lab especially.
As an undergrad, Wang had attended a lecture by David Sibley, and he later kept showing up in the professor's office, brimming with questions about Toxo. Sibley became his mentor for the better part of the next decade.
In that time, Wang would learn what it feels like to be the rube.
Though Toxo appears to live a quiet life of dormancy in most of its hosts, the bug is no pacifist. Every year in the U.S., there's an estimated one million new infections, and about 200,000 of those lead to illness. Along with the parasite's lethal effect on fetuses and newborns, studies continue to find statistical links between Toxo and some mental illnesses.
Some theories seem to tilt at windmills. Czech scientist Jaroslav Flegr has made a career out of Toxo behavioral studies. In a 2007 paper, Flegr concluded that the infected stood a higher chance of dying as pedestrians in car accidents. A different study by Flegr suggested that infected subjects "expressed higher attraction to nonconventional sexual practices," including "bondage, violence, zoophilia [and] fetishism." Flegr even theorized that his own tendency toward risk-taking and self-destruction was, perhaps, connected to the Toxo inside him.
Flegr's studies make headlines, but scientifically, they're dubious. Sibley recounts a dinner he once shared with some colleagues and Flegr. At the table, the Czech scientist claimed he could predict a man's Toxo status from his choice of timepiece.
As Sibley tells it, Flegr "had this idea, that for men who are seropositive, their personal hygiene standards relax. They're very disgruntled and anti-authoritarian. They dress more shabbily, and so they wear like a broken Timex watch. And if they're seronegative, they wear a Rolex."
Flegr's theory turned out to be easy to test; all the researchers at the table knew their Toxo status.
"We went around the table to see who was wearing what watch," Sibley says, laughing. "It turned out he was 100 percent wrong."
Wang's obsession with Toxo didn't carry him quite as far as Flegr. Wang wanted to know about dopamine, a discrete, measurable component that could be converted into numbers and analyzed, reviewed and eventually turned into answers that would be stamped into science textbooks and journal pages. Or so he hoped.
The Sibley Lab wasn't the only lab attempting to create engineered parasite strains missing the H1 and H2 genes, but Wang was the first to knock out H2. Four years later, with the help of an advanced genome editing tool called CRISPR, he did the same to H1.
In the meantime, however, Wang was having trouble replicating the influential 1985 study on which he'd based his own experiment. Try as he might, he couldn't detect a significant swing in dopamine inside the brains of mice infected with the standard strain of Toxo.
Wang was flabbergasted. It was like dropping an apple and watching it float off your hand and into the clouds. The dopamine theory hinged on the basic assumption that Toxo changed dopamine levels.
"I wound up running face-first into the wall of, 'I can't replicate any of this,'" he says.
Wang kept trying, which involved removing the brains from dozens of mice, grinding the individual organs into paste and then measuring the dopamine content. Over time, the possibility for error or fluke hardened into near-certainty. The data was sending him a message.
"If you squint real hard and ignore the error bars, then maybe there was an increase," Wang concedes, "but the increase wasn't significant." And in any case, the increase wasn't anywhere near the level claimed in the widely cited 1985 study.
Wang spent months, then years, trying to account for the discrepancy. Perhaps he had simply been unlucky, producing outlier results that weren't representative of what was really happening in the brains of zombified rodents. Maybe only H1 was fiddling with dopamine levels, and H2 was a red herring. Somewhere, he thought, there must be a mistake.
Over time, he says the rival labs that were looking into the dopamine theory quietly moved on to other projects. "These things didn't replicate in their lab, either," he suggests.
With the help of the precision gene-editing capabilities of CRISPR, Wang eventually mastered the cut-and-swap of H1 and H2. He could cut it from Toxo and replace it at will. If those genes functioned like a dopamine lever that controlled mice, sending them to their doom, they should behave as one.
They didn't. Present or absent, the genes didn't change the amount of dopamine in the infected mouse brains.
There was one other test to try. It was a test that would attempt to evaluate the dopamine theory by using Wang's genetically modified Toxo strain, but in an environment that had nothing to do with cats or their urine.
In 2014, Wang shipped samples of his homegrown strain to a lab at Johns Hopkins University. There, scientists infected mice with the mutated parasites. Then the researchers injected their furry test subjects with cocaine and amphetamine.
Why the hard drugs? Previous experiments demonstrated that Toxo infection tends to blunt the hyperactive effects of the high. In mice, as in humans, those effects are primarily controlled by dopamine. In a lab environment, scientists can track and measure the drug-addled rodents' physical movements, and that data allows them to make conclusions about the dopamine levels during the coke party. Wang hoped the results would show that his earlier tests had missed something, that science's previous assumptions about Toxo — and its puppet-master pull on dopamine — were based in reality.
But after cranking up the infected mice up with big doses of both stimulants, the rodents infected with Wang's mutant strain showed no difference than those infected with normal Toxo. Clearly, the parasite wasn't using those genes as a lever to control the flow of dopamine. In Wang's hands, the basic premise of Toxo's mind-control power had floated away.
Wang and Sibley started publishing their early results on the dopamine hypothesis in 2015. The Johns Hopkins lab published its results this year in Behavioral Brain Research.
To Sibley and Wang, these studies appeared to be the nails in the coffin of the dopamine theory. The results rocked the Toxo scientific community, forcing researchers — particularly those investigating ties between Toxo and mental illness — to consider alternative mechanisms to dopamine.
Wang certainly isn't the first graduate student to blunder into a theory and wind up staring at its wreckage. But it still leaves researchers with no choice but to start back at the beginning.
"We don't have good candidate for a simple explanation that would replace the dopamine idea," Sibley acknowledges.
The truth is, Toxo's behavior lends itself to a vast number of branching hypotheses and interpretations, and the bug's presence in billions of people means that it can be shown to correlate with any number of things. Could Toxo really be behind schizophrenia? Or depression? Or implicated in untold millions of car accidents? Could it really be manipulating the type of watch you wear?
Maybe, says Sibley. Maybe not.
"On one level it sounds crazy, but there might be something to it. It does cause chronic infection in the brain. It could alter behavior and maybe it makes you less fearful and you step in front of a bus."
What Sibley is certain of, however, is that scientists will continue to perform association studies that draw correlations between Toxo and human behavior, especially psychiatric illness.
"The thing is," he adds, "is that we don't really have a way to alter those outcomes, even if they're true."
Without dopamine, a cogent, simple theory of cause and effect, scientists are left stumbling, searching for a new light to illuminate Toxo's darkness.
Like any good magician, Wang doesn't reveal the secrets behind his tricks. The day after his gig at the benefit gala, Wang shuffles a deck of cards onto a table at a Soulard cafe. Late-morning sunlight streams onto the succession of numbered cards and tranquil royal faces, and the pieces of painted cardboard seem to glow.
"The secrets of magic are ugly," Wang says, squaring the deck in his hands. "They're not entertaining and they're not enjoyable. They're pretty much universally disappointing."
Still, on the condition that the details of his specific methods remained concealed in publication, Wang runs through one of his tricks for a reporter, spelling out each step, each misdirection, each sleight of hand.
He's right about the disappointment, of course. The trick creates, in Wang's words, "impossible suggestions" of movement and space. To a normal audience, it is a captivating wonder that looks like, well, magic — especially when Wang rattles off several variations of the impossible in a manner of seconds.
In fact, the trick is built on several verbal lies, tactical use of body language and blazing-fast hand speed. Wang has spent years training to accomplish more in a half second with one hand than most people could do with five minutes. Even if you know what he's doing, his movements are hard to track.
Visually, the card is resting in your hand. You can feel the glossy surface pressed between your fingers. You can see it entering into a deck at a particular point, and moments later it's in an impossible location on the other side of the table, in a different deck of cards entirely.
Of course, the real magic is happening in Wang's hands, too fast for the eye to detect.
It takes four demonstrations — the final attempt done at quarter-speed — for this slow reporter to finally wrap his head around the mechanism behind the "magic." In a moment, the truth is obvious, and it is a definite let-down. It leaves a sudden stabbing embarrassment. You feel dumb for missing it before.
Wang tries to be reassuring, but he knows, in a way, what it's like. The death of his dopamine hypothesis was crushing. It forced him to wrestle with years of built-up expectation.
Over seven years working towards his Ph.D, Wang had imagined how this breakthrough could make his work famous. He could see the headlines in his mind. "Parasite Turns Rats Crazy: Here's How It Does It."
"I never wanted anything more," Wang says. He's put his cards away. He notes that a Toxo lab in England, which was behind the widely cited 2009 study supporting the dopamine theory, published a 749-word critique of Wang's journal article, alleging his experiment showed methodological and technical flaws. Wang and Sibley responded with a 1,716-word rebuttal.
Other labs are still actively investigating Toxo's link to schizophrenia, and some scientists continue to find interesting links in the parasite's spread to humans. Going forward, though, Wang (and Sibley) consider dopamine a broken hypothesis.
"The stack of evidence has piled up to suggest that whole dopamine idea is wrong, it's pretty high," Wang says bluntly. "It's pretty robust. I wouldn't expect good results at continuing to hammer at it."
Still, it's not like Wang's research produced nothing. As detailed in a 2017 study published in the journal PLOS Pathogens by Wang and colleagues at the U.S. Department of Agriculture, the work on dopamine uncovered something new about H1 that didn't have anything to do with dopamine. Instead, USDA scientists found that H1 actually supplies key materials for building the protective shell around Toxo spores during the reproductive stage inside cats.
When H1 is sliced out of Toxo, the spores are left vulnerable. Without the protection of a sufficiently thick shell, the parasite isn't viable outside the cat.
"It turns that [H1] is not just a precursor to dopamine, it's also a precursor to a lot of structural proteins," Wang explains. "It's probably a precursor of the outer shell that the parasites use to go dormant and form a spore and survive in the environment."
It's not a world-shattering discovery, but it's one in line with the steady, drip-by-drip process of research that's traditionally come out of the Sibley Lab. And there's possible relevance for a future treatment: If the parasite's reproductive cycle can be disrupted, it could stop Toxo's spread.
Asking Wang — or any scientist — to broadly speculate about their work is usually a tricky proposition. At some point, the conversation crosses a line into story and myth, and that's how you get experiments framed around belief and assumption. The story of Toxoplasma is still being written, and, sometimes, erased.
The future of the research continues, in the Sibley Lab and in similar labs across the world. And the tiny parasite continues to be one of the most successful parasites on Earth, reproducing, forming spores and spreading to more hosts. What it's doing in the majority of its human hosts, we still don't know.
Those discoveries could lie years or decades in the future, and it shouldn't be a surprise when new, promising hypotheses arise claiming to unlock the parasite's secrets. Wang has seen Toxo's tricks up close, and he knows how seductive a single, perfect answer can be.
"We all want to see the world the way we believe it to be. It's just human," he muses. "We're so much better at identifying evidence that confirms things we believe already."
For now, Wang — who earned his Ph.D. in 2017 — splits his time between his lab and his magic. During the workday, he investigates and catalogues the physical properties of the world, while on the nights and weekends he gives every appearance of violating the laws of physics with a stack of painted cardboard paper. Every week, Wang the Mentalist leaves a new audience gasping at tricks that they know, deep down, can't be real.
Wang has embraced this life of performative deception, and with it attention and applause. Still, the mystery of Toxoplasma is never far from his mind. The question remains: What is Toxo really doing in the human brain?
It's not for Wang to answer. The next round of discoveries will fall to some other researcher. A scientist with some other beautiful theory. Next time, if they watch closely, they just might glimpse the blur of the parasite's hands.