Mind-Controlling Parasites Will Shape the Future

The next revolution in understanding the brain is nigh, and it will pivot on cells first observed under a microscope almost 350 years ago: bacteria.

The first clue, for me, was toxoplasmosis. Or backing up even further, the first hint was a scene from BBC’s Planet Earth, which gave my older sister a severe case of the creeps, in which an ant infected by the fungus cordyceps becomes disoriented, seeks higher ground, dies, and becomes the spawning ground for the next generation of fungus. I was fascinated rather than freaked out, but not for the reason I should have been; I suppose I believed that only ants and insects could have brains simple enough to be hijacked by an infection, and couldn’t imagine this happening to the human brain.

Then came toxoplasmosis, an infection caused by a protozoan parasite that seeks a cat’s intestines the way salmon seek their own place of birth to spawn. Instead of fighting their way up raging rivers whilst trying to avoid grizzly bears, though, the Toxoplasmosa gondii make themselves comfortable in a rat – specifically in a rat’s brain, where it will make the rat sexually attracted to cat urine (quite the crazy fetish in the rat world), increasing the odds that the rat will be eaten and the protozoan will be the one that gets to reproduce. And its not just rats, but humans too, and in more disturbing ways than a mere fetish: it might increase suicide rates, contribute to schizophrenia and even road accidents, and subtly alter your personality. It’s one thing to think that having a cat growing up might have influenced me because cats are fun and furry, and another to think it influenced me by giving me a brain infection.

The second clue was PANDAS, or “pediatric autoimmune neuropsychiatric disorders associated with streptococcal infection” – or in laymen’s term, strep throat causes obsessive-compulsive disorder. I found out about this as a “medical mystery” a year ago, and explored one parent’s story in great depth this summer reading “Saving Sammy“. It isn’t the strep infection itself that causes OCD symptoms, but the immune system’s response to the strep infection; some immune systems over-respond, and start attacking a region of the brain called the basal ganglia. It seems impossible that this could create compulsions as intense as seeing invisible walls that must be stepped over or refusing to use the front door of the house (some of Sammy’s milder symptoms), but the evidence is striking. Everything we “know” about psychiatry says that antibiotics shouldn’t cure OCD, but in these cases it does.

The third clue, the tipping point that makes me think a revolution is approaching, links autism as well to an immune response. This is not quite so simple as PANDAS as toxoplasmosis, because there is no clear single infection at the heart of the disorder, just another compelling piece to a puzzle that an immune system out of whack (too willing to inflame in response to an infection) often enough goes hand-in-hand with an autism diagnosis. It could be a major part of the rise of autism diagnoses in recent years, as our heavily disinfected environments improve our survival rates but perhaps leave our immune systems improperly tuned.

None of these claims are really new: There are published articles linking toxoplasmosis to schizophrenia as early as 1966, PANDAS dates back to 1998, and a quick glance found a study looking for an autoimmune contributor to autism in 1986. What is new is a shift toward accepting these claims, a growing trend of connections across different domains (schizophrenia, OCD, autism) and with different root causes (toxoplasmosis, strep, or unspecified infections) with enough cases and studies that skeptics cannot simply dismiss them out of hand. The snowball is rolling forward, and for the first time I will get to watch, over the years, as it becomes an avalanche. The specific studies may be wrong, the infections or immune response may not turn out to be the most important thing, but the idea of looking to the immune system to treat something that’s supposed to be in the mind? Right now, it is inconceivable to teach a single course on psychology without discussing the brain, at least the basics of how it functions and what neurons are. Ten or 20 years from now, it may be inconceivable to teach any course on psychology without addressing the immune system, and how specific infections or general responses to them can affect the way we behave.

Or as the quote from Men In Black goes: “Fifteen hundred years ago everybody knew the earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and fifteen minutes ago, you knew that humans were alone on this planet. Imagine what you’ll know tomorrow.”


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