The patient's family asks, "what causes schizophrenia?" And you give them the speech: "there are probably many causes: genetics, some say an in utero infection, or in the old days they said it was the schizophrenogenic mother." And then chuckle like you possess any knowledge that allows you such dismissive confidence. I'm not saying it's true, I'm saying you have no idea if it's true.
The problem is that those aren't all potential causes of schizophrenia, they are causes of different kinds of schizophrenia, none of which you are making any attempt to distinguish.
Toxoplasmosis is an organism that lives part of it's life relatively benignly in the intestine of a cat, gets pooped out, and then taken up by rats where it lodges in the brain, not benignly. That's the cycle, back and forth. It also can be taken up by humans, especially little fetuses.
Going from cat to rat is easy. But how is it supposed to get back to cat? Rats run away from cats, not towards them. Indeed, this is innate: even rats that have never seen a cat in hundreds of generations still freak out when confronted with cat odor.
There's been plenty of research observing that schizophrenics are more likely to have been exposed to toxoplasmosis in utero than normals. So what? So this.
Researchers took 60 rats, and infected 30 with brain munching toxoplasmosis (verified at the end by autopsy) and the other 30 with terrible, evil saline. And then they gave them a choice of scented cages to explore. The scents were either: their own, water, rabbit, or cat.
Comparing infected to non-infected rats, there was only one difference in their preference for cage exploration:
i.e. the infected rats are insane.
Note that the toxoplasmosis didn't make them more exploratory in general, only dispatched them to their likely doom. (No, it didn't interfere with their sense of smell.)
Taking the most active infected vs. non-infected mice, and watching them over multiple explorations, not only do they not avoid the cat cage, but they develop a preference for it over other cages:
One might say that toxoplasmosis is a chronic, worsening condition characterized by poor judgment...
The rats don't simply defy danger; they specifically want to die by cat. Rats can also get killed by minks, but minks don't hunt them. A similar study gave rats a choice of mink maze and cat maze, the infected rats chose cat-- they chose their specific predator.
It's a truly odd coincidence that while the cat is the mortal enemy of the rat, the cat is the natural home of toxoplasmosis. One might even be tempted to say that somehow the toxoplasmosis willed the rat to go against its nature. "That's dangerous talk around here, lefty, better mind your tongue." Apologies.
But the other way to look at it is
Studies investigating the neurological basis of anxiety, which often use the reaction of potential prey to cat stimuli as a model, have found that blocking the normally anxiogenic N-methyl-D-aspartic acid receptors in the amygdala, and/or provision of serotonin (5-HT) antagonists, causes rats to approach cat odors "fearlessly," in much the same way that T. gondii-infected rats do.So the rats become less anxious, more daring? Odd coincidence: the toxoplasmosis infection rate in 1974 was 22% for the Brits, 84% for the French. Maybe it makes humans chase pussy as well?
Lafferty, in 2006, found rates of 45% in the French and 6.6% in the Brits. How have people changed since the 1970s? Maybe the reason "there are no real men" is because all the antibiotics have "sterilized" them.
Let's assume that these studies show causation and not simply staggeringly awful correlations. The semantic problem posed here is that you could choose to label the toxoplasmosis as either "schizophrenogenic" or "anxiolytic." Both are equally valid, by which I mean completely meaningless. The only thing you know for sure is that it was caused by the toxoplasmosis.
Toxoplamosis is not a cause of schizophrenia, it is a cause of toxoplasmosis infection. The schizophrenia part never existed.
If all this wasn't troubling enough, there's this:
Following a similar model as above, a group of infected rats were also given the treatment for toxoplasmosis (pyrimethamine and Dapsone). Predictably, this cured the rat and stopped their crazy cat seeking behavior.
However, so did Depakote and Haldol, sometimes even better:
Look at this as the chance of being in the cat cage. a) is all behaviors, and b) teases them out. You can see that untreated rats like cat cages, treated rats don't.
What happened? There's the obvious behavioral explanation (Haldol treated the psychosis); though Haldol does also block toxoplasmosis growth and infection.
Which means if you gave Haldol to a "schizophrenic," and saw "improvement," you would not really know if it was blocking D2 receptors or killing parasites.
And what would you have assumed had the Depakote worked?
No one says syphilis is a cause of schizophrenia, but the same people would say toxoplasmosis is. I hope you see there is no difference.