Guided by Parasites: Toxoplasma Modified Humans

by Tobias on June 4, 2010

Above is a ~20 minute (absolutely worth every minute) interview with the leading researcher, Dr. Robert Sapolsky, in the study of Toxoplasma & its effects on humans. This is a must see. [click here to read the full text of the interview]

“…this is a protozoan parasite that knows more about the neurobiology of anxiety and fear than 25,000 neuroscientists standing on each other’s shoulders…” – Dr. Robert Sapolsky

Toxoplasma (Toxoplasma gondii) [Toxo] was first observed in 1908. You may have heard of it as the crazy parasite that makes rats attracted to cats.  This, in its own right, is astonishing, interesting, & bizarre. It has also been widely known that pregnant women should stay clear of cat scat & other sources for Toxo as it can adversely affect the development of the fetus.

Dr. Robert Sopalsky at Stanford has taken this link to humans further & has been studying, in detail, how it is affecting humans with some startling observations, but we’ll get to that later.

Dr. Sapolsky, Professor of Neurology and Neurological Sciences, is known for his work studying the biological effects that stress has on primates, including humans. In addition to his research at Stanford, he annually spends time in Kenya as a research associate at the National Museums of Kenya researching the effects of stress on a population of baboons for well over 20 years.  His research has lead to hundreds of scientific publications & six books including the acclaimed Why Zebras Don’t Get Ulcers, Monkeyluv: And Other Essays on Our Lives as Animals, A Primate’s Memoir: A Neuroscientist’s Unconventional Life Among the Baboons, and others.

Toxo Life Cycle (click for high res)

In order to understand how it affects humans, one must first understand how it affects its desired hosts: cats and rodents.

“Toxo knows how to hijack the sexual reward pathway.” – Dr. Sapolsky

For a parasitic protozoa it has a remarkably complicated and fascinating life cycle. The quick summary is that Toxo can only sexually reproduce in the gut of a cat. The cat then excretes Toxo in its feces which is then consumed by the intermediate hosts (e.g., a rat). Once in the rat Toxo’s goal is to then be eaten by a cat so it can be fruitful and multiply, but as I mentioned, this can only take place in the cat’s gut. Toxo’s goal is to get the rat eaten by a cat.

Toxo could get the desired effect through a whole sort of seemingly obvious ways; e.g., Make the rat hard to run so it is easier for a cat to catch it.  Instead it takes a far more interesting approach:

Toxo generates cysts in the brain of the rat. These cysts take over the fear center of the brain, but specifically the fear of predators. Common fear sources for rodents (e.g., bright lights, open spaces, etc.) still operate perfectly well in an infected rat, but now they are no longer afraid of cat piss.

That alone would be cool enough, but Toxo takes it one step further. When Toxo is going about futzing with the fear center of the brain it also goes into the sexual excitement part of the brain. It hijacks the incoming Fear of Cat Piss™ and instead diverts the signal to the Barry White™ center of the brain.

“Somehow, this damn parasite knows how to make cat urine smell sexually arousing to rodents, and they go and check it out. Totally amazing.” – Dr. Sapolsky

The rat is now sexually attracted to cat piss!

(This is a fetish that gets you eaten by your predator and rats clearly do not have any safe words with cats.)

On top of all this, Toxo apparently has been hanging out in hipster bar bathrooms doing lines of blow off of some cat’s ass. The parasite has the mammalian gene for creating dopamine (which I have discussed in brevity previously):

Cocaine works on the dopamine system, all sorts of other euphoriants do. Dopamine is about pleasure, attraction and anticipation. And the Toxo genome has the mammalian gene for making the stuff. It’s got a little tail on the gene that targets, specifies, that when this is turned into the actual enzyme, it gets secreted out of the Toxo and into neurons. This parasite doesn’t need to learn how to make neurons act as if they are pleasurably anticipatory; it takes over the brain chemistry of it all on its own.” -Dr. Sapolsky

This is all good fun for fucking with the behavior of rat brains, but is there anything that crosses over into the human realm? This is the question that Dr. Sapolsky’s team has been working on.

What does Toxo do to humans? And there’s some interesting stuff there that’s reminiscent of what’s going on in rodents.” – Dr. Sapolsky

It seems that humans aren’t having love affairs with cat piss. Instead, it appears that humans are having the fear center of their brain circuit bent causing some interesting findings.

A small literature is coming out now reporting neuropsychological testing on men who are Toxo-infected, showing that they get a little bit impulsive. … And then the truly astonishing thing: two different groups independently have reported that people who are Toxo-infected have three to four times the likelihood of being killed in car accidents involving reckless speeding.” – Dr. Sapolsky

In a very specific example, Dr. Sapolsky goes on to state that motorcyclists have a high probability of being infected with Toxo. I wonder if my friends who have a love for motorcycles grew up with cats and therefore had a higher probability of being exposed.

“…if you ever get organs from a motorcycle accident death, check the organs for Toxo. I don’t know why, but you find a lot of Toxo.” – Dr. Sapolksy

It is stunning that human behavior is being modified by a parasite that wasn’t even intended for humans (“off label use” perhaps?). This appears to be pure happenstance.

I am left wondering, “What if there is a parasite out there that specifically uses humans as their hosts?

If a simple organism can make such precise modifications to a rat’s brain, it is not far fetched to think that this is already going on inside our heads on a far larger scale.  It would appear to me that we have only scratched the surface.

It appears that we are far more affected by our surroundings, things we ingest, exposure to compounds, (e.g.,Epigenetics) and now parasites than many originally thought. Our DNA appears to be the hand we are dealt, but how those cards are played seem to be under the control of far more players than many had originally assumed.

I have some sideline questions I would love to have answered:

•How do you test for toxo?
(I would love to be able to find out if I have any in my system, for example.)

•How does one test for dopamine activity in the brain without resorting to trepanation?

For those interested in more of Dr. Sapolsky’s works, which I highly recomend, here is a video of a talk he gave at Stanford last year about “The Uniqueness of Humans“.  It is an absolutely wonderful talk that equally knocks us down a peg or two at the same time it rises us like a yeasty bread such that the pegs that are missing are now merely holes to push tasty cream cheese into.

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