There is a parasite, Toxoplasma gondii that is found in cat feces. Serological studies suggest that almost one third of the global population has been exposed to and may be chronically infected with this parasite. Infection is typically asymptomatic in healthy adults.

T. gondii has been shown to alter the behavior of infected rodents in ways thought to increase the rodents' chances of being preyed upon by cats.

“Because cats are the only hosts within which T. gondii can sexually reproduce to complete and begin its lifecycle, such behavioral manipulations are thought to be evolutionary adaptations to increase the parasite's reproductive success. In one of the manifestations the evolutionary biologist Richard Dawkins attributes to the "extended phenotype". Although numerous hypotheses exist and are being investigated, the mechanism of T. gondii–induced behavioral changes in rodents remains unknown. A number of studies have suggested subtle behavioral or personality changes may occur in infected humans, and infection with the parasite has recently been associated with a number of neurological disorders, particularly schizophrenia. However, evidence for causal relationships remains limited.”

The phenomenon of the “crazy cat lady” has been attributed to severe infection with T. gondii in the female brain.

I love cats, so does my family. Since as early as I can remember we have had at least one, and usually more than one cat living in and around my household. As a research microbiologist I had always been fascinated by the phenomena of parasitism. Although I ended up specializing in bacteriology I followed closely the most ground breaking research in the field of parasitology. When the connection between T. gondii and cat feces was first hypothesized I became obsessed with learning everything I could about this strange parasite and its relationship with our friendly felines.

The implications for mental health seemed especially interesting. In addition to its supposed role in schizophrenia, T. gondii has been linked (albeit weakly) with increased risk for anxiety, depression, and a host of other mental afflictions. Higher rates of substance abuse among cat owners, especially with cats that are infected with T. gondii, have also been shown. I suffer from severe anxiety and my sister has had numerous mental health issues. Interestingly, my parents do not appear to be affected and are very healthy both mentally and physically. I would note however that neither of my parents grew up with cats in the household. It may be there is an age of exposure component to the pathology of conditions (potentially) caused by T. gondii.

As I got older, my mental condition continued to deteriorate. Chronic bouts of anxiety and depression became more frequent. At the same time I experienced periods of severe mania usually accompanied by habitual substance abuse. Somehow, I managed to keep my job in research as I drifted in and out of treatment programs and rehabs. Though my research was in an area far afield from parasitology, T. gondii was never far from my mind.

The more I read, the more I learned, the more convinced I became that all of my mental ailments could be attributed to a chronic infection by this fascinating yet nefarious microorganism.  In the back of my mind a pervasive dread slowly began to form.  If T. gondii infections caused rodents to alter their behavior in a way that made them more appealing as prey to cats, could it be doing the same to me?  The behaviour of my beloved felines seemed unchanged, though in my confused and distressed mental state I sometimes felt they were spending an inordinate amount of time staring at me with a look of (hunger?) in their eyes.  

At some point my behaviour became too bizarre for any employer to tolerate and I was let go from a series of well-paid and prestigious research positions. My reputation and productivity was not enough to compensate for the strains I put on the various institutions who hired, and then shortly thereafter, fired me.

Looking back now, I can understand why. I've had plenty of time to think since being committed to Hocking Hills mental asylum. The lack of eyesight contributes to my contemplative nature. Having your eyes clawed out and then eaten by your former "pets" would lead anyone, I believe, to struggle to maintain their sanity. Even after it happened, I begged and pleaded with the authorities to save my cats. They are not to blame. It was T. gondii. They were simply following their instincts. Don't blame my cats. Don't ever blame my cats.