Toxoplasma is a science non-fiction nightmare. Closely related to the malaria-causing parasite, the plasmodium's eggs find their way into rats that nibble on the faeces of infected cats. After living inside the rodent, when it's time to reproduce, the parasite has to get into a feline again.

Rats are pathologically averse to cats; the mere smell of one is enough to drive them away. So how does toxo make the jump from prey to predator? Without touching any of the other functions, the parasite severs particular neurons in the rat's brain making them fearless of cats. A neurosurgeon par excellence!

The parasite then goes even further, fiddling with a neural pathway in the brain so the smell of cats becomes sexually alluring! The poor rodent throws caution to the winds and flaunts itself! Harakiri! Toxo hits the jackpot, and can now merrily reproduce. But, this is only one of the world's diabolical devils.

Have you heard of hairworms? The thin-as-a-strand-of-hair worm grows inside grasshoppers, and after it matures, it doesn't take the easy way out through the cloaca. Instead, it messes with the grasshopper's brain leading it to commit suicide. The poor insect leaps headlong into a puddle of water with all the confidence of an expert swimmer only to drown, while the hairworm wriggles free to reproduce.

And, then there is a barnacle, Sacculina, which rides piggyback on crabs. When it comes time to lay eggs, the barnacle needs a hole in the sand. Being incapable of movement, how does it do that? First, Sacculina renders the crab impotent so the latter nurtures the parasite's eggs as its own. Then the barnacle controls the crab to do its bidding and digging. Voila!

But, what puts toxo in a class apart is not only widespread prevalence, but its wicked effects on humans. Most people do not get infected by cats directly, but by eating uncooked meat, drinking unsafe water, gardening without wearing gloves, and walking barefoot. A few years ago, suspected contamination of the municipal water supply led to an outbreak of toxo in Coimbatore.

Globally, as many as a third (may be more) of the human population is suspected to be infected with the disease. In India, 45 per cent of pregnant women tested positive. Despite these radical numbers, it is not front page news as is H1N1. That's because toxo is not believed to be fatal to healthy humans, nor is it infectious. But, if you are a baby, or your immunity is lowered by drugs or disease, then toxo can take your life.

What toxo does to healthy humans is alter their personalities. Infected men become morose, jealous, and introverted with high levels of testosterone, while it makes women outgoing, animated, and warm. As Nicky Boulter of the Sydney University of Technology puts it: “It can make men behave like alley cats and women like sex kittens.”

The sting at the end of the toxo tale is: it makes both men and women reckless and uninhibited. Toxo-muddled human beings are three times more likely to be involved in road accidents than others; perhaps, to them, other vehicles look like gigantic cats! So, the next time you see yet another suicidal person on the road and grumble: “What's with them?” you now know!

Here's a startling thought: humans may not be a dead-end for the parasite. Infected men may be more likely to fall prey to wild tigers and leopards in our forests and farmlands, while toxo-influenced women are likely to pass on the disease to their babies. My over-active and possibly parasite-enslaved brain wonders if the testosterone-driven men across the world who taunt venomous snakes are infected too? And, suicide bombers?

Toxo is so widespread that scientists believe it may be manipulating human culture! Countries with high infection rates also suffer higher rates of neuroses. Parasitico diabolico!

(The author can be reached at janaki@gmail.com)

Keywords: Toxoplasma

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