New news on cat urine


“Mr. Pickels, we should get that nice Professor Singleton to change your litter box”

I was over at the vet’s office on Friday, and while I was waiting for Happy the Hamster to finish up with her exam, I noted this news alert from up on the office wall, with the intriguing headline “Good kitty, Good science, Bad journalism”.  The editorial took the national news media to task for their reporting of an extensive behavioral study from the journal JAMA Psychiatry (note: free access to the article if you get to it via the YCP Library page). The study followed a cohort of over 45,000 women in Denmark over the period of time from 1992 to 2006, and examined the question as to whether Toxoplasm gondii infected women were at any higher risk for self-directed violence or suicide. The story was widely reported when it came out, and according to, inappropriately slanted the findings of the study to overemphasize the potential risks due to Toxoplasma infection. My interest in this story reflects both my role as a litter-box cleaner, and as a student of the dangers of Toxoplasma

Here is the Danish study in a nutshell: 45,778 Danish women were enrolled in a study from between 1992 and 1995, shortly after giving birth. At this time, blood was drawn from the infant to determine whether the subject was asymptomatically infected with the protozoan parasite Toxoplasma gondii. Because newborn babies do not produce antibody themselves at this time, the presence of Toxoplasma specific antibodies in the baby’s circulation result from the passage of antibody from the mother across the placenta prior to birth. Subjects were followed through a blinded study (investigators never knew the identity of any of the subjects), and assessed for self-directed violence, suicide attempts, and suicide.

The study found that approximately one quarter (26.8%) of the population was seropositive for Toxoplasma antibodies, suggesting potentially sub-clinical infection. Of the 45,000 subjects followed through the study period (over half a million person years), researchers found that 488 had a first contact for some indication of self-directed violence. These subjects were then followed up through the remainder of the study period regardless of their serological status to Toxoplasma. When seropositive and seronegative subjects were finally compared at the end of the study, it was found that seropositive subjects (i.e. those who had a positive titer of antibody to Toxomplasm gondii at the time of their child’s delivery) had a 1.53-fold higher risk of committing a violent act against themselves. The authors of the study propose a potential mechanism to explain the results, and suggest that an inflammatory response designed to keep the pathogen in check might cause activation of certain neuronal cells and lead to behavioral changes. The authors note that the study cannot distinguish between the direction of causation–an alternative hypothesis might be that a preexisting neuroimmune abnormality might make an individual more susceptible to Toxoplasma infection.

Note: women can safely change the litter box after they are no longer pregnant

Toxoplasma infection (over one quarter of the women enrolled in the study!), it makes no attempt to identify the source of their infections. Cat feces are certainly an important route of transmission, and indeed if you go to the Centers for Disease Control and Prevention’s site on toxoplasmosis, cats are the first animal mentioned on the page, and they explicitly recommend that if you are pregnant you should have someone else clean the cat box. However, with such a high rate of infection, a more significant risk of infection are other environmental sources such as gardening in soil that is contaminated with the organism.


About ycpmicro

My name is David Singleton, and I am an Associate Professor of Microbiology at York College of Pennsylvania. My main course is BIO230, a course taken by allied-health students at YCP. Views on this site are my own.

Posted on September 15, 2013, in Danger danger danger!, Wash your hands! and tagged , , . Bookmark the permalink. Comments Off on New news on cat urine.

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