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Cat Parasite May Increase Risk of Suicide In Humans
An anonymous reader writes "Researchers at the University of Maryland analyzing meticulous data collected by Danish authorities have identified a positive correlation between suicides among women with infection with the fairly common parasite T. gondii. Carriers were 53 percent more likely to commit suicide in a sample of 45,000 Danish women monitored for over a decade (researchers believe that the same correlation likely exists for men). Increased susceptibility to schizophrenia and bipolar disorder was also discovered. The physiological mechanism has not been determined, although some speculation centers around changes to dopamine levels. Two intriguing aspects were noted: 1) human infection often (but not always) begins by exposure to cats carrying the parasite, for example, by changing an infected animal's litter; and 2) the parasite spreads itself by infecting the nervous system of rodents, causing them to become suicidally attracted to feline odors which will increase the likelihood of their hosts being eaten by cats, whose digestive tracts provide the preferred environment for parasite reproduction."
Do the crazy cat ladies have cats because they are crazy, or are they crazy because they have cats?
Suicidally? Being attracted to something known to shorten your lifespan doesn't mean you're suicidal. Take one example: Americans gorging themselves on McDonald's, then flooding hospitals with heart disease cases in an attempt to stay alive. If they were suicidal, they'd just keep eating more burgers and look emo about it till they died.
The Danish study is just the latest in a long series of studies which demonstrate a correlation between toxoplasmosis seropositivity and psychiatric problems-- it's been linked to schizophrenia and ADHD, and so on. Wikipedia has a good article on the topic.
It's pretty interesting. Apparently something like 10% of the US population is seropositive for toxo. The infection is thought to be "contained" immunologically, but encysted organisms are still present in muscle and nervous tissue, and the process of "containment" may induce a subtle inflammatory state which affects a broad variety of neurotransmitters (not just dopamine). It's also possible that the causation works the other way-- the people who get chronic infections may have something about their immune system that is different to begin with, and the difference might predispose them to psychiatric problems independently of toxo infection. Good discussion of all that in the Danish study, which was published in Archives of General Psych and seems to be non-paywalled.
What will be really interesting is to see what happens if you identify psychiatric patients with chronic toxo and try to eradicate the toxo with antibiotics-- do their psych symptoms improve? There have been at least two studies I could find (one where it helped and one where it didn't), and apparently there's a large-scale study getting started in the UK.
For people who are wondering, it looks like they didn't have a good control group. So here is how they answered some potential objections:
1) What if depressed people get cats, and that's why they have the parasite? Did they check people who have cats but aren't depressed?
It's probably not related to cats, because most people who get this parasite get it from undercooked meat.
2) What if depressed people are more susceptible to this parasite because they are depressed? What if non-depressed people are capable of fighting off the parasite with a stronger immune system?
There was no correlation between people who had the parasite, and people who had a history of mental illness. (Also, correlates with other studies, that might have had better control groups, I'm too lazy to check them out to see).
"First they came for the slanderers and i said nothing."