The Atlantic Magazine
How Your Cat Is Making You Crazy
JAROSLAV FLEGR IS NO KOOK. AND YET, FOR YEARS, HE
SUSPECTED HIS MIND HAD BEEN TAKEN OVER BY PARASITES THAT
HAD INVADED HIS BRAIN. SO THE PROLIFIC BIOLOGIST TOOK HIS
SCIENCE-FICTION HUNCH INTO THE LAB. WHAT HE’S NOW
DISCOVERING WILL STARTLE YOU. COULD TINY ORGANISMS
CARRIED BY HOUSE CATS BE CREEPING INTO OUR BRAINS,
CAUSING EVERYTHING FROM CAR WRECKS TO SCHIZOPHRENIA?
By Kathleen McAuliffe
Image credit: Michal Novotný
NO ONE WOULD accuse Jaroslav Flegr of being a conformist. A self-described
“sloppy dresser,” the 63-year-old Czech scientist has the contemplative air of
someone habitually lost in thought, and his still-youthful, square-jawed face is
framed by frizzy red hair that encircles his head like a ring of fire.
Certainly Flegr’s thinking is jarringly unconventional. Starting in the early 1990s,
he began to suspect that a single-celled parasite in the protozoan family was
subtly manipulating his personality, causing him to behave in strange, often self-
destructive ways. And if it was messing with his mind, he reasoned, it was
probably doing the same to others.
The parasite, which is excreted by cats in their feces, is called
for short) and is the microbe that causes toxoplasmosis—the
reason pregnant women are told to avoid cats’ litter boxes. Since the 1920s,
doctors have recognized that a woman who becomes infected during pregnancy
can transmit the disease to the fetus, in some cases resulting in severe brain
damage or death.
is also a major threat to people with weakened
immunity: in the early days of the AIDS epidemic, before good antiretroviral
drugs were developed, it was to blame for the dementia that afflicted many
patients at the disease’s end stage. Healthy children and adults, however, usually
experience nothing worse than brief flu-like symptoms before quickly fighting off
the protozoan, which thereafter lies dormant inside brain cells—or at least that’s
the standard medical wisdom.
But if Flegr is right, the “latent” parasite may be quietly tweaking the connections
between our neurons, changing our response to frightening situations, our trust in
others, how outgoing we are, and even our preference for certain scents. And