Meet Toxoplasma Gondii: The Love-to-Hate Parasite

My relationship with my cats took on a slightly different quality on this week two years ago.

That's when I first heard the parasites episode of Radiolab and learned about Toxoplasma gondii, a parasite that lives in cat guts and confuses the brains of small critters and potentially humans. More on that later.

My relationship with my cats also took on a slightly different quality six months ago.

That's when we learned I was pregnant and I turned the duty of changing the cat litter over to my husband.

“This is my least favorite thing to do every day,” he moaned Friday as I snapped the picture to accompany this column — a picture I'll one day to frame to prove it ever happened. (To his credit, first complaint about it so far.)

So what's the big deal with Toxoplasma gondii (said like Mahatma)?

Well, for one thing, it can have serious or even fatal effects on a fetus whose mother first contracts the disease during pregnancy. More than 60 million Americans carry the parasite, though the immune system usually keeps it from doing any damage. However, the CDC lists it as one of the five Neglected Parasitic Infections now targeted for public health action.

Cat guts are the only place the parasite can reproduce sexually, so transmission occurs through cat feces, as well as undercooked meat or unwashed vegetables.

Like anyone else, a woman first infected during pregnancy may not exhibit symptoms, but fetal diseases of the nervous system or eyes can result, according to the Centers for Disease Control and Prevention. (There's the “really good source” you asked me to find for this column, honey. Now how are we doing on litter supply?)

But Muppet and Sister have been indoor cats since kittenhood. How may they have contracted the parasite?

Hunting in the house, I learned from Radiolab.

Toxoplasma gondii gets its legs from small rodents — rats, mice, birds — that sometimes snack on cat feces. Over six weeks, working within the little critter, Toxoplasma gondii physically links the areas of the brain that control fear and sexual arousal. The rodent then has no fear of cat urine, maybe even seeks it out — and where there's cat urine, there's cat, so rodent easily becomes cat cuisine.

With the infected critter now delivering the parasite to its gut, the cat can spend up to three weeks shedding millions of Toxoplasma gondii eggs in its feces. Humans accidentally ingest the eggs after cleaning an infected litter box or touching or consuming anything contaminated...and voilà.

Granted, if my cats had swallowed the parasite any time during their 10 years, odds were good I'd already been infected by this past March. But just to be on the safe side, my doctor told me at my first prenatal appointment to have someone else change the litter box for the duration of my pregnancy.

Thanks to Radiolab, I'd already turned over the pooper scooper.

If the brain-control aspect of Toxoplasma gondii doesn't creep you out yet, consider that science has also linked it to schizophrenia — the numbers of which skyrocketed when humans started keeping cats as pets — death by car accident and suicidal behavior in women. (Thankfully a study published this month debunked a theory that it also causes brain cancer.)

And if it rewires critter brains, can it also make humans exceptionally passionate about felines?

Science still doesn't know, but I'll tell you one thing that helps: someone else cleaning up their mess.