People in love often behave in wacky, weird and often bizarre ways, eliciting amused smiles from those who’ve been there (and survived), and scowls from the bitterly envious. But few of the smitten can match what goes on in the love life of a very primitive (we would think) protozoan (a single-celled creature) called Toxoplasma, or Toxo, for short.
The best and only haven in the whole wide world for Toxo to have its honeymoon is in the gut of cats, or other felines. In these and only these salubrious surroundings, Toxo reproduces sexually and gen-next is promptly crapped out by the cat, into its litter box or the ground. Here, they wait and wait and wait. They may die waiting, longing for the cosy intestines of a cat, where romance can blossom once again. If they’re inordinately lucky, a rat or mouse comes by, snuffling this way and that, and, perhaps, picks some of them up, say, by coming into direct contact with them on the ground or maybe snaffling up a seed that has been contaminated. Once it infects the rodent, Toxo goes to work in a manner that would make Machiavelli seem like a rank amateur.
From the gut of the rat, Toxo slowly heads towards the brain of the rodent, for the part called the amygdala — where the fear and anxiety circuits of the brain are located and operate. Here, normally when a rat smells a cat (or cat urine), stress hormones are released, activating the circuit and instinctively prompting the rat to flee. What Toxo does is that it begins to unravel and take apart this circuit so that it cannot function normally. What’s diabolical is that it shorts only the circuit devoted to fear of predators; other fear circuits are left untouched, so the rodent remains the same in every other way: it continues to be afraid of large open spaces and bright lights and behaves completely normally. But now, because its flee-from-predator response has been rendered null and void, it has become a bit of a bindass rat or mouse, one that is no longer afraid of pussycats and ready to take on even lions, tigers and leopards, perhaps.
If that was not foolish enough, wait for what’s coming. Toxo doesn’t leave it just at that. The amygdala also has circuits going through it (and thereon to other parts of the brain) which deal with pleasure and sexual arousal, which have to do with the presence of the neurotransmitter dopamine (which is all about anticipation, pleasure, reward and attraction). Toxo comes equipped with two genes which produce the enzyme critical for the manufacture of dopamine and excretes this into the hapless (soon to be haplessly in love) rodent’s brain. Suddenly, fear and loathing of cats is turned into cat love and desire. The rakish rat (whose balls actually get bigger!) goes looking for pussy cats, sniffing out that wonderful aphrodisiacal perfume: cat’s piss. (They’re still trying to figure out how this works with lady rats).
For a cat, crouching down, lashing its tail and watching a smitten mouse or rat swagger up to it, drunk with love, well, dinner is served. And Toxo finds itself back in the honeymoon boudoir where it all began a long time ago.
Well, you might think, as long as you’re not a rat you have nothing to fear. Not so fast. It’s been thought that, perhaps, as many as one third to half the human population is infected with Toxo too. We get it from walking barefoot or eating food that hasn’t been properly washed or from carelessly handling cat litter boxes. And yes, it can be deadly for pregnant women because it messes up the brains of their babies.
Most adults merely report mild flu-like symptoms when they first encounter the parasite, but now more sinister discoveries are coming to light. It’s been found that Toxo might make men behave recklessly too: infected men have a far higher risk of getting into road accidents due to reckless, fast driving. (In which case, 99 per cent of Indian drivers probably have it!) Then there’s a suspected link to schizophrenia: because schizophrenics have far higher amounts of dopamine in their brains than normal, and assisting its manufacture happens to be one of Toxo’s specialties. The armed forces know about Toxo and that can never be a good thing. You can well imagine a scenario where soldiers are deliberately infected with Toxo and sent out on hare-brained suicidal missions.
And then, look at the rabies virus which goes about doing much the same thing but in a much more barbaric and bestial way. Once inside a victim, the virus hits the neurological system, irritating the victim beyond endurance and making it snarl, snap and bite. The virus knows that the infected victim is doomed, and so, just before the biting starts, transfers itself to its salivary glands so that it gets passed on to what will now be the victim’s victim: the person or animal that it bites, thus ensuring its own survival — a sort of macabre game of tag, if you will.
It is a bit terrifying to think that these virtually invisible parasites and viruses can manipulate our behaviour like this; so much for free will and thinking that the animal kingdom consists of “poor dumb creatures”. These are just two — god knows how many thousands more there are out there, already pulling our strings and making us do what they want, just so they can have a jolly good roll in the hay!
Ranjit Lal is an author, environmentalist and bird watcher.