Parasite

to his mother, eyes narrowed and angry. “There’s a point where it stops being science and becomes wishful thinking.”

“Toxoplasma gondii,” said Dr. Cale.

Nathan’s irritation faded, replaced first by horror, and then by an expression of sheer disbelief. “You’re telling me you spliced Toxoplasma into the genome?”

“Among other things, but it’s the Toxoplasma we need to worry about right now.” Dr. Cale beckoned for us to follow as she turned her wheelchair and began making her way toward one of the workstations. Adam walked beside her chair, while Nathan and I followed her. Tansy stayed behind to turn off the light boxes set into the wall. It seemed strangely responsible for someone so flippant, until I realized that letting the rest of us go ahead would give her access to our backs. I felt a lot less comfortable after that.

Then again, I hadn’t really felt comfortable since this whole thing began. Maybe a little more discomfort wasn’t such a big deal. I kept a firm grip on Nathan’s elbow, and followed Dr. Cale to the workstation.

The workstation had clearly been designed with accessibility in mind: the path to it was wider than usual, and there was more space below the desk, allowing her to pull her wheelchair all the way into place. Three computer monitors were arranged in a loose half circle, each of them displaying a screensaver of abstract loops and whorls of color twining endlessly around one another. Dr. Cale put her hand on the mouse, saying, “Scientists have known for years that the Toxoplasma parasite was capable of modifying the human mind in surprising and seemingly impossible ways. It still took us a long time to come around to that way of thinking. We didn’t realize Toxoplasma was capable of causing symptoms that mimicked schizophrenia, for example, until someone proved it.”

Nathan glanced at me. Apparently interpreting my expression as confusion, he said, “Toxoplasma is a common feline parasite. A lot of cat owners have it. Some people think that may be where the crazy cat lady stereotype comes from.”

“I know,” I said. “I work in an animal shelter, remember? I had to attend a hygiene class where we learned all about toxoplasmosis and how to avoid it.” Once a toxoplasmosis infection set in, it was virtually impossible to get rid of. The Toxoplasma parasite preferentially colonized the human brain, and most infections were mild enough that the cure was considered worse than the disease. Any antiparasitics strong enough to address the infection in the brain would wreck the host’s immune system, as well as killing off any more helpful parasites that might be in residence. It was an unnecessary risk. So we all wore gloves when we cleaned the cat boxes, and we were all careful around new cats, and things continued. But if the SymboGen implants contained Toxoplasma DNA, that changed everything.

I just wasn’t sure exactly how.

“I’m glad we’re all on the same page, then.” Dr. Cole opened a series of pictures, one on each monitor. One showed a tapeworm, curled in a large receptacle, as if prepared for dissection. Adam paled and looked away.

“Your original specimen?” I guessed.

“The portion that was removed from my body during the surgery,” confirmed Dr. Cale. She turned enough to pat Adam’s arm reassuringly. “That was long after the portion that would become Adam had been removed.” I got the feeling she added her last line as part of an ongoing argument, one where Adam blamed himself for her injury, and she tried, over and over again, to make him understand that it could never have been his fault.

The second screen showed a petri dish at thirty times magnification. It held a scattering of small parasites. Nathan frowned, leaning a little closer to the workstation. Dr. Cale leaned to the side, letting him get a clear view.

“The morphology is wrong,” he said. “They should be shorter and squatter, with no defined separation between segments.”

“This generation of Toxoplasma gondii had already been combined with some of the more desirable genes from the other creatures that would be contributing to the development cycle,” said Dr. Cale. “By this point, it was beginning to achieve a greater size, and seemed less interested in entering the brain, which was, you can imagine, rather important to us. Imagine the havoc a fully grown tapeworm could cause by attempting to migrate through the human body.”

“Havoc like seizures?” I asked very quietly. “Or like losing motor control and seeming to go to sleep while you’re still awake?”

“Havoc a great deal like that,” said Dr. Cale. The third monitor showed a blue crab for some reason. She tapped a key on the keyboard at the center of the desk. The image of the crab began to move, performing an odd stirring gesture in the water with its large front claws. It bobbed up and down as it stirred, looking content, if a crustacean can ever be said to experience contentment. “This was our last major contributor.”

“The crab?” asked Nathan. “Mother. Mom. I’m willing to believe that you combined two species of parasite and injected them with human DNA, but my willingness to ignore the laws of nature only extends so far. There’s no way you introduced crustacean DNA into the mix.”

“I didn’t. The crab isn’t a member of our donor species. This is a male blue crab infected by Sacculina carcini.”

“Same problem,” said Nathan, with the sort of dismissiveness I normally only saw him direct at orderlies who didn’t want to listen during his rare ER shifts. He didn’t want to hear what she was telling him. “Sacculina is a barnacle. It’s still a crustacean, and I don’t care if you’re a scientific genius, Mom. You’re not God.”

I guess having a lifetime of memories telling you how the world works is a lot more difficult to get past than six years of often-conflicting explanations. “Why can we combine parasitic worms and humans, but not parasitic worms, humans, and crustaceans?” I asked.

“Biology is tricky, Sal,” said Dr. Cale. “A lot of the rules are more like suggestions, or can be, if you come at them from the right angle, but you still want to break as few of them as possible. Break too many, and the chances that everything will go catastrophically wrong increase at an exponential rate.”

“We don’t count as things going catastrophically wrong,” said Tansy brightly, as she popped out of the darkness behind us. I jumped. Nathan didn’t, but from the way he tensed, it was a near thing. Tansy beamed. “We’re a natural evolutionary modification to an artificially created organism.”

“As I was saying,” said Dr. Cale. “Sacculina carcini is a crustacean, but it’s also one of the most dramatic examples of parasitic castration found in anything larger than a cone snail. It literally takes over and rewrites its host, turning a perfectly healthy crab into an incubator for the parasite’s own egg. One of the more interesting tricks in the parasitic castrator’s repertoire is the feminization of its host. You see, male blue crabs are aggressors. They’re likely to go out and get themselves hurt before the Sacculina babies can properly mature. That does the parasite no good at all—and neither does the production of sperm, which simply routes nutrients away from the Sacculina. So the parasite fixes all that by controlling the blue crab’s biology. It’s a very small creature, very primitive, and it still has the skill to turn a male crab into a female one, at least externally.”

“But you didn’t use it,” I said.

“No—we couldn’t, nice as that would have been. Barnacles simply weren’t compatible with the work that we’d already done. We would have needed to start over with something purely crustacean, and that would have made the human interface infinitely more difficult. Mr. Blue Crab here is simply intended to make a point.”

“And what’s that?” asked Nathan sharply.

“That parasites can control behavior on a much deeper and more integrated level than most people want to give credit to.” She tapped the keyboard again. The waving blue crab was replaced by an image of a simple flatworm. It was almost see-through, displayed in the classic backlit simplicity of a parasitology manual. “Meet Trichobilharzia ocellata, a member of a large, diverse family of trematode worms. They’re parasitic castrators, just like Sacculina carcini, although they’re biologically much closer to tapeworms. Much, much closer, after a little careful modification by yours truly.” Her smile held pride and regret in equal measure. “I’m very good at what I do. I always have been.”

Nathan stared at her like he couldn’t believe what he was hearing. “You mixed Toxoplasma and a parasitic castrator into the genetic makeup of the SymboGen implant?”