When I wrote about the parasite Toxoplasma gondii a couple of years ago (The Great Brain Robbery; MetroPlus, October 16, 2010), some readers’ emails were incredulous, while a few were sceptical. An orthopaedic surgeon serving a prison sentence said he had never heard of anything like it. Since it’s only in recent years that research has revealed how toxo affects humans, I sent him the various scientific papers I had collected.

Another reader commented: “Why isn’t this the plot of a zombie movie? That’s incredible that it infects humans like that, and as I was reading I paused midway through to think about what would happen if such a parasite could control people with as much repetitive ease as those other animals, and quickly, and obstinately shuddered away the idea as improbable, only to have you lead up to that a few paragraphs later.”

There’s at least one fictional story in the works. The jailed orthopaedic was so excited, he said: “It gave me an idea for a lovely science fiction story which I completed writing in a single sitting.” The man is reportedly India’s most prolific pulp fiction writer in English.

However, I find the protozoan’s real life propensities more fascinating than any fictional story.

For readers who missed the earlier article: This protozoan lives in rats but reproduces in cats. In order to move from prey to predator, toxo manipulates rodents’ brains so the animals are not only fearless of cats, but actively seek out their nemesis. Humans, who eat uncooked meat, and drink contaminated water, can also get infected by the parasite. It causes personality changes and a range of mental disorders in us.

A new study published in June 2012 concludes that those infected with toxo were one-and-a-half-times more likely to kill themselves. The scientists followed nearly 46,000 Danish women over the course of 14 years. The more toxo antibodies floated in their blood, the more violent the means they chose to end their lives. With one million suicide deaths a year worldwide and as many as 10 million attempts, this finding has tremendous implication on saving lives.

Why does a rat-cat parasite affect us so dramatically? Toxo cannot differentiate between rats and humans. So it does to our brains what it would do to a rat’s with bizarre results.

I’ve always wondered if we are really a dead-end for the parasite that health experts make us out to be. Our chances of being eaten by cats is almost nil, but we evolved in the savannas of Africa where large cat predators prowl. Leopards and other big felines consider our primate cousins prey, and in many places, humans are taken down by these cats.

In November 2011, a team of scientists led by Jaroslav Flegr, a Czech scientist at the forefront of toxo research, wrote that infected men were attracted to the smell of house cat urine. But the same men found the smell of tiger piss unpleasant. I find that odd. Numerous tiger hunters, biologists and zoo keepers have compared the smell to the fragrance of cooked basmati rice. I’ve never smelt it myself to give you an opinion.

Why would toxo cause men to be repulsed by tiger urine when that’s the only way it can find its way into a cat? Toxo is not fussy about cat species; any feline, pet cat or tiger, would serve its purpose. Perhaps testing victims of tiger and leopard attacks for the parasite will tell us more.

Strangely, toxo-infected women were put off by the smell of cat urine. Doesn’t the parasite trapped inside women want to reproduce? We don’t yet know much about this microscopic creature’s manipulation of humans.

But it is becoming more and more apparent that infected people are being taken for a ride. And the creature in the driver’s seat is not human.