John scratched his chin and frowned in an exaggerated manner, as if deep in thought. “I don’t know, maybe a wolf or a fox?”
Sarah shook her head, taking advantage of the pause to eat more.
“Maybe a mountain lion—or some big predator that eats sheep? Humans?”
“You’re cold,” said Sarah. “Think smaller.”
“Okay,” said John, drawing out the last syllable of the word and rolling his eyes toward the ceiling. “If it’s not a predator of the sheep, then maybe it’s something that eats the snails? A bird or something?”
Sarah shook her head again, clearly enjoying the game. “Nope, nothing that eats the snails or the sheep.”
“If it doesn’t eat the sheep or snails,” said John, handing Sarah another piece of garlic bread, “and the snail already eats something from the sheep, then it’s gotta be something that the sheep eats. But, sheep eat grass and plants—does this Dicro-whatever—I already forgot its name—but does it live inside plants, maybe? Or an aphid or something like that?”
“No, but you are so close!” said Sarah, laughing. “The third host is ants. When they found out that it was ants, scientists were even more puzzled. Dicrocoeleum begins its lifecycle in the intestines of sheep, and it is excreted in sheep dung and left on the fields, right?”
John nodded. “Yeah, that much I got. And snails eat the sheep dung. It’s kind of gross to be talking about this at dinner, you do realize that?”
“Oh, sorry,” she said, blushing.
John chuckled. “It’s all right, you’re good. Just kidding. Go on.”
“Right, okay. Well, the organism needs to reproduce inside the snails so that part was easy. But then it also needed to live in ants for part of its lifecycle.”
“A rather inconvenient requirement if you ask me. So, pray tell, how does Dicro go from snails to ants? Do ants regularly make meals of live snails? Or maybe, I know, they eat the dead snails,” he declared triumphantly.
“Awesome answer, but nope, wrong again,” said Sarah.
They had both finished eating now, but they were still sitting at the table. They often lingered this way, talking for hours. It was one of the many things Sarah loved about their marriage.
“All right, Dr. Spallanzani, I almost hesitate to ask, but do tell,” he said beckoning her to come sit on his lap.
She didn’t know why, but nothing seemed to turn him on more than a mental challenge. “Well, Dr. Chadwick, you may not believe this, but it turns out that the species of ant that Dicrocoeleum likes to live in is partial to snail slime.”
“Ugh! Now that is really gross.”
“You’re telling me!” she said, laughing, and then darted her eyes sideways, as if she was revealing highly classified information, and lowered her voice. “But did you know that snail slime is high in protein?”
“Umm, no, but I can just see it now in one of those health food shops. ‘Would you like some snail slime to go with your alfalfa smoothie, sir?’”
Sarah burst out laughing, which made him laugh too.
“So the ants go and gather balls of slime and take them back to their ant hills. The Dicrocoeleum, which had been living in the snail’s gut is released in the slime, so when the ants eat it, they get infected. So far so good,” said Sarah, rolling her neck as he began massaging her shoulders. “But, the problem is that the last stage of this parasite requires them to return to living in sheep, and sheep don’t eat ants.”
“Don’t they?” he asked, nibbling one of her ears.
“Pay attention,” said Sarah, turning to face him.
“Okay, sorry,” he said. “Ants don’t eat sheep.”
“John!”
“All right! Don’t get upset! And sheep don’t eat ants. I got it. So this Dicro-dude is screwed.”
Sarah shook her head and crossed her arms dramatically, feigning annoyance unconvincingly.
“Well, are you going to finish your story?”
“Do you want me to?” she asked.
“Actually, what I want you to do is, hmm,” he said, giving her a meaningful glance, “but it can wait. Please tell me now how the ants get into the sheep,” he said wrapping her in an embrace.
“Well, as you probably know, sheep eat only the top of the grass or plants, which is why they are great natural ‘mowers.’”
“That’s true!” said John enthusiastically.
Sarah looked at him questioningly.
“I mean, I remember hearing on the radio how the city of Los Angeles had hired a shepherd and his sheep to ‘mow’ all the grass on the hills around the city and it was so much cheaper and better for the environment… anyway, yeah, let’s finish your story.”
Sarah smiled. “Okay, so sheep eat the tops of plants and ants hang out on the ground or under the ground.”
John cocked an eyebrow at her.
“So, it’s sheer genius of nature. The Dicrocoeleum, once eaten by the poor unwitting ant, chews through its intestine and enters into its nerves, traveling to its anterior ganglion—the ant brain, if you will.”
“I do know what an anterior ganglion is!”
“Of course. Once it gets there, it changes the ant’s natural behavior. Instead of being geotropic, you know, loving being in holes in the ground, it makes the infected ant become negatively geotropic.”
John stared at her for a moment. “So, what are you saying? The ant goes and hangs out at the top of plants…”
“You got it! No self-respecting sheep is going to go around eating ants—they are strictly vegetarian.”
“Of course,” said John in a teasing voice, massaging her shoulders again.
“But if an ant is hanging out at the tip-top of a grass blade, it will ‘accidentally’ get eaten, thus completing the lifecycle.”
“Whoa, now that is pretty cool,”
“Amazing and absolutely true.”
John thought for another moment. “So, mice that are braver because they have the Toxoplasmosis infection…”
“…are more likely to get eaten by cats, thus completing the parasite’s lifecycle,” said Sarah.
“I see,” he said. “Okay, that makes sense. That’s what those research articles were saying.”
Sarah got up and sat in a chair so that she could face him.
“But your story here leads me to wonder,” he said, “if the parasite could be having an effect on human behavior as well?”
Sarah nodded. “One of the crazy suggestions that came up at the meeting was to inoculate people with Toxoplasmosis—or Toxospasmosis, as Angela calls it—to protect them from Laptev, but if it is causing behavioral changes or even mental illness, then it would be all the more reason why we don’t want to get more people infected. Can you imagine the disaster if more people, even non-cat owners, were infected with an organism that can cause them mental illness in order to protect them from the virus?”
John nodded. “You’re right. It could be a bad situation. It would make no sense to do that.”
“I know, but I can’t help wondering if maybe there is a way to control the cat pathogen so that it doesn’t make us ill? We already know that there are tons of people with low-level infections, and the vast majority of these people are not crazy.”
John looked at her skeptically.
“Well, everyone is a little crazy, infections notwithstanding, but you know what I mean,” said Sarah. “Look around. Tons of people own cats. The vast majority of these people aren’t a menace to society. But if there are people out there who are Laptev HFV-resistant, that could be a real advantage. I’m thinking that I would like to get blood samples from those people and test the samples against the virus. It would be great to know which ones are more resistant and why. And of course we could investigate what other effects Toxoplasmosis has on their lives. Are they living longer or shorter lives? Is it affecting their behavior in any way? Which reminds me, Emile mentioned that Toxo affects men and women differently. Do you know anything about that? ”