Is schizophrenia caused by Toxoplasmosis?

[Nick Theodorakis]

Toxoplasma gondii is a parasitic protozoan that can infect a number of mammals, including humans, but cats are a major reservoir for the organism. Toxoplasmosis can cause flu-like symptoms in healthy adults, but it is a major risk factor for stillbirth or spontaneous abortion if a pregnant woman contracts the disease.

There has been an idea kicking around for a number of years that Toxoplasmosis is a risk for factor for, or perhaps even a cause of, schizophrenia or other psychiatric disorders. This bulletin from the CDC is six years old, but summarizes much of the data that accumulated by that time. Toxoplasma is known to infect the brain and can cause a chronic infection that can last for years. A number of epidemiological studies have also indicated that patients with schizophrenia are more likely to show evidence of past infection with Toxoplasma. Rodents infected with Toxoplasma undergo specific behavioral changes (see also here).

One possible mechanism that may allow the Toxoplasma to contribute to psychosis is that the organism produces an enzyme called tyrosine hydroxylase, which is key enzyme in the production of the neurotransmitter dopamine, as reported here. (Elevated dopamine is associated with schizophrenia).

More recent reviews on the link between Toxoplasmosis and schizophrenia can be found here, here, here, or here.

Nick

[llewtrah]

We discussed this on the board a few years ago when it was almost a scare story. The problem was - some people with existing schizophrenia might keep cats as companions rather than having gotten toxoplasmosis and developed symptoms after keeping cats. It could be coincidental, not cause and effect.

[DawnStorm]

All cats don't harbor the parasite, or do they? If any of my bosses had the parasite, their vet certainly would've told me by now.
Regardless, I always wash my hands after cleaning their boxes; that's because I've been scooping used litter though.

[Tarquin Farquart]

Louis Wain is often mentioned in this context.

[Logoboros]

Originally Posted by DawnStorm

All cats don't harbor the parasite, or do they? If any of my bosses had the parasite, their vet certainly would've told me by now.
Regardless, I always wash my hands after cleaning their boxes; that's because I've been scooping used litter though.

Your vet wouldn't necessarily know. Cats can harbor toxoplasmosis without having any symptoms or illness themselves. Unless the cat is specifically tested for it (and they usually aren't, unless they're ill), you wouldn't know.

Also, the transmission risk is small, but your cat licks its butt, it then licks you or you nuzzle it: bingo, you have a route for human infection. Not much you can do to avoid that, though, so washing hands after handling litter is at least the next best thing. Of greater concern is if you have a garden and you cat is defecating in the soil that you're getting food from. There's a much higher risk of infection by that route than casual contact.

[CDC factsheet]

[Toxo in cats]