A small subset of suicide attempts may be linked to an infection that starts in the litter box. A new study suggests an association between Toxoplasma gondii and suicide attempts among women.

Interesting finding, to be sure, but how does one even begin to test a theory like this? Why in the world would anyone posit that kitty litter could be related to suicide attempts?

As it turns out, about one-third of the population is walking around right now with latent toxoplasma infection. Most people will never know they have it - and most will not attempt suicide as a result of it. But the presence of T. gondii among women who attempted suicide raises interesting questions.

Those questions led senior study author, Dr. Teodor Postolache, to find out more. Postolache said he was at first puzzled by studies suggesting low-grade activity in the immune systems of suicide victims.

"We were puzzled," said Postolache, associate professor of psychiatry and director of the Mood and Anxiety Program at the University of Maryland School of Medicine. "We wanted to know what could contribute to that activation."

As he later discovered, T. gondii is associated with schizophrenia and, in other studies, associated with suicide.

So he and colleagues decided to take a closer look at a group in Denmark, where they already had an ongoing allergy study, and where patient data is meticulously kept. Their T. gondii study was conducted among 45,788 women in Denmark between 1992 and 1995.

What Postolache and colleagues found is that women infected with T. gondii had one-and-a-half times higher risk of attempting suicide when compared with women with no infection. According to the study, published Monday in the Archives of General Psychiatry, "the risk seemed to increase with increasing... antibody level."

So, the more antibodies found in the blood reacting to T. gondii, the higher the risk of a suicide attempt.

Postolache tempers the finding by pointing out that the chances of having T. gondii infection and never attempting suicide is much higher than attempting it.

"This is a very prevalent parasite, a very successful parasite, that affects one-third of the world population," said Postolache, a senior consultant on suicide prevention for the Baltimore VA Medical Center. "One-third of them are not attempting suicide."

True, but another scientist says that results of this study represent the "tip of the iceberg" in terms of answering broader questions, like could infections like T. gondii contribute to mental disorders?

"There's a strong association between certain types of infection at certain times in life and various psychiatric problems," said Dr. Charles Raison, associate professor of psychiatry at the University of Arizona in Tucson.

"We have these simple ideas about infection and illness like you get the influenza virus and then get the flu. One bug equals one illness. What we now know is it's much more complicated than that. Infections can produce a lot of secondary effects," he added.

In the context of the current study, that means T. gondii may not be causally linked to increased suicide risk, but a more global and complex process may begin with infection.

"It appears that toxoplasmosis does things that unbalance emotional mental functioning," said Raison, CNNHealth.com's mental health expert. "Depending on other risk factors, maybe it makes you depressed, maybe it makes you impulsive."

But before you usher your kitty (along with its offending litter) out of the pet door, consider that those (many and complex) other factors - not just the T. gondii - are likely at work in the mind of a person who ultimately attempts suicide.

"All those factors may interact with or moderate the T. gondii," said Postolache. "Investigating that will be important."