You’ve all seen her: The “crazy cat lady” with her disheveled hair, hoarder-style home, dumpster diving and–of course–the telltale parade of cats following behind her like the pied piper.
But why cats and not some other animal? Cat hoarding, while not listed in the DSM, is associated with mental illness. Cats carry a parasite known as Toxoplasma gondii, or T. gondii for short. It can only reproduce in the bodies of cats but often passes to humans and other animals.
So is cat hoarding an evolutionary trick that allows T. gondii to thrive? We’ll return to that in a minute.
Toxoplasma has a natural affinity for the brain and can have fatal consequences in the offspring of pregnant women. Cerebral palsy, seizures and mental retardation are a few possible outcomes of maternal exposure. This is why pregnant women are advised against changing litter boxes.
In the human brain, T. gondii creates an enzyme that interferes with dopamine function. Schizophrenia–viewed in psychiatry as one of the most serious disorders–is highly associated with abnormal dopamine function. A number of studies have shown a direct statistical link between schizophrenia incidence and toxoplasmosis.
But all you sane cat lovers out there needn’t worry. A large percentage of the population is infected with T. gondii and does not have mental illness. How you respond to the infection depends on a number of factors, including your genetic makeup, immune function and the timing of infection. In the early days of AIDS, toxoplasmosis was a major killer in immune compromised patients. It often caused “AIDS-related dementia” or blindness in its hosts shortly before killing them.
So how is T. gondii transmitted? It can be acquired by touching cat feces, eating raw/undercooked meat or even handling soil while gardening.
But back to the evolutionary function of cat hoarding. A strange phenomenon can be seen in rats infected with T. gondii: instead of running from the scent of cats as they normally do, it causes them to lose their natural fear and even seek them out. In this sense, T. gondii has hijacked the rat’s brain for its own purposes. (Remember: toxoplasma can live in many animals but only reproduces in cats). Cat then eats rat, re-infecting itself with the parasite and completing the circle of life. [Cue Lion King music]. There’s a good chance the same thing is happening inside the brains of cat hoarders.
That’s one smart parasite.