The Loom

Toxoplasma on the Brain

i-4580f3baf0665914fe035e4b7148d671-toxo200.jpgNext time I go to the doctor, I think I’ll get him to give me a test for Toxoplasma. Fifty million Americans have the parasite, so I wouldn’t be the first. And if I was carrying it around in my head, that might explain why it’s so fascinating to me.

I first encountered the strange ways of this single-celled creature while working on my book Parasite Rex, and since then I’ve tried to keep up with new research on what makes it so successful. In January I wrote on the Loom about a potential link between Toxoplasma and schizophrenia.

In Tuesday’s New York Times I have an article that surveys some of the newest work on this bug–how, for example, it turns our immune cells into Trojan horses to get into our brains, and how it can precisely manipulate its hosts to hurtle to their doom. If you prefer your parasites podcasted, I’m chatting about Toxoplasma on the June 20 podcast for the Science Times. You can access it through the Times web site here, or through Itunes. Get infected by ear or eye–your choice.


  1. #1 John Wilkins
    June 20, 2006

    So, can it be treated? Does it respond in the cysts to broad spectrum antibiotics? Can I blame it for my total laziness? Enquiring minds…

  2. #2 Carl Zimmer
    June 20, 2006

    Sulfa drugs are standard treatment for acute infection, but pretty harsh. Some people looking into the schizophrenia link want to try artemisinin, which is less harsh. (It’s an antimalarial drug–Toxoplasma and Plasmodium are related.)

  3. #3 michelle thomas
    June 20, 2006

    I’m curious if the broad spectrum anti-PS mab currently being investigated at NIAID would be applicable, since the parasite avoids innate immune recognition through exposed phospatidylserine.

  4. #4 michelle thomas
    June 20, 2006

    I’m curious if the broad-spectrum anti-PS mab currently being investigated at NIAID would be applicable, since the parasite avoids innate immune recognition through exposed phosphatidylserine.

  5. #5 Jason Malloy
    June 20, 2006

    Toxoplasmosis is scary stuff:

    Jaroslav Flegr, the professor of parasitology behind the research at Charles University in Prague, . . . says, that toxoplasma infection and subsequent delayed reaction times were linked to a greater risk of traffic accidents. “If our data are true then about a million people a year die just because they are infected with toxoplasma,”

    Infection relates to double or triple the amount of car accidents, (presumably) from slower reaction times.

    Both car accident rate and reaction time are related to IQ, so I Pubmed-ed it, and sure enough, toxoplasma is also associated with lower IQ scores. (I wonder if the path runs the other way? Hygiene propensity, perhaps.)

    Anyway I further regret my past associations with cats.

  6. #6 Carl Zimmer
    June 21, 2006

    Thanks, Jason–I tried to squeeze the personality stuff into my article, but there just wasn’t room. The parasite is too damn cool for its own good.

  7. #7 Chad Okere
    June 24, 2006

    I wonder if all there all kinds of crazy animals living in our bodies that havn’t been discovered yet because they don’t cause problems. Obviously viruses, but could something as large as a eukaryote live in humans undetected?

  8. #8 John McCoy
    July 31, 2006

    I propose the following hypothesis:

    Toxoplasma controls rat and mouse behaviour by releasing (or stimulating the release of) dopamine whenever serum adrenaline levels spike. This causes infected rodents to become “adrenaline junkies” or thrill seekers. They linger in areas smelling of cat urine because it thrills them to do so. This is not willful or conscious behavior, but a simple chemical response that conferred a survival advantage. Toxoplasma exhibits the same behavior in humans, even though it does the organism no good. It just does this whenever it is not in a cat.

    This could account for much human self-sabotaging, self-destructive or thrill-seeking behaviors. I am pretty sure it explains my pathological procrastination. I have been conditioned by Toxoplasma to behave in ways that will make authority figures threaten me. (My father yelling at me for not finishing my homework. My boss threatening to give me a bad review). Perhaps criminals carry this to less civilized extremes. We’re all just tempting the big cat to eat us.

    Perhaps toxoplasma is the root of all evil.

  9. #9 Robert Heinlein
    February 24, 2007

    Does anyone know if toxoplasmosis has an extended neural net?

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