A recent study in Denmark implicates an infection spread by cats in causing humans to feel suicidal.
The infection is called toxoplasmosis. It is caused by a parasite found, among other places, in the GI tracts of cats. Therefore, contact with cat feces when emptying a cat’s litter box is one way humans can get it. Other ways include eating undercooked meat.
We have known for some time that toxoplasma antibodies (proof of exposure to the parasite) seem to be elevated in patients with schizophrenia.
Now, the Dutch study has found an increased rate of suicide attempts in those with the infection. The study, which looked at 45,000 pregnant women in five counties in Denmark found that 27 percent of them showed antibodies to toxoplasma.
Among that 27 percent (as opposed to the other 73 percent of women), self-destructive violence was more common by about 50 percent. And the higher the antibodies to toxoplasm (presumably showing a more significant exposure), the greater the risk. Those with the highest level of antibodies were at almost 100 percent higher risk for self-harm.
The actual completed suicide rate was over twice as high in women who had been exposed to toxoplasma as those who had not. Since the total number of suicides was only 18 in the population of 45,000, absolute conclusions are tough to draw, but more experiments should certainly be conducted.
One reason toxoplasma could trigger severe psychiatric symptoms—including suicidal ideation—is that it causes inflammation in the central nervous system, raising the levels of inflammatory compounds like interleukin-6. Those inflammatory compounds may be neurotoxic.
For now, my guidance for patients who have owned or cared for cats is to consider toxoplasma as potentially playing a role in thoughts of self-harm, which don’t seem to be treatable with standard medications and psychotherapy. In such cases, going to see a physician who specializes in infectious disease, armed with your concern about toxoplasma, would be a reasonable step.
Treatment of the infection isn’t without side effects. But, if your psychiatrist and infectious disease doctor agree, going forward with treatment may make sense as one part of an overall strategy to ward off self-destructive impulses.